1. A system for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, the system comprising: an engine control unit communicatively coupled to at least one gaseous fuel injector, an ignition system, and an exhaust gas sensor positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine; wherein the engine control unit is configured to: acquire a plurality of engine operating parameters including at least engine speed and engine load; generate a base fuel injection command based on a feed-forward fuel map and the acquired engine operating parameters; command the at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine based on the base fuel injection command; receive an air–fuel ratio signal from the exhaust gas sensor indicative of an air–fuel ratio of combusted gases; compute a deviation between the received air–fuel ratio signal and a target air–fuel ratio; derive an adaptive fuel correction value based on the computed deviation; apply the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio; determine whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold; and upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, command the ignition system to retard an ignition timing relative to a base ignition timing.

2. The system as claimed in claim 1, wherein the engine control unit is further configured to store the adaptive fuel correction value in a two-dimensional adaptive fuel learning map indexed by the engine speed and the engine load, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map.

3. The system as claimed in claim 1, wherein the engine control unit is configured to derive the adaptive fuel correction value based on the computed deviation in combination with historical injector opening duration data associated with the at least one gaseous fuel injector, and wherein the engine control unit derives the adaptive fuel correction value when predefined fuel learning conditions are satisfied, the predefined fuel learning conditions including at least one of: steady-state operation of the internal combustion engine, absence of knock in the internal combustion engine, validity of sensor signals associated with the internal combustion engine, and operation of the internal combustion engine within predefined temperature ranges.

4. The system as claimed in claim 1, wherein, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the engine control unit commands the ignition system to retard the ignition timing by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold.

5. The system as claimed in claim 1, further comprising a non-volatile memory communicatively coupled to the engine control unit, wherein the engine control unit is configured to: store the adaptive fuel correction value in the non-volatile memory; retain the stored adaptive fuel correction value in the non-volatile memory across successive engine start and engine stop cycles of the internal combustion engine; and apply the stored adaptive fuel correction value to the fuel injection commands upon a subsequent engine start to reduce transient deviation between the received air–fuel ratio signal and the target air–fuel ratio.

6. The system as claimed in claim 1, wherein the exhaust gas sensor is a wideband-type lambda sensor configured to measure the air–fuel ratio of the combusted gases over a range extending from lean conditions to rich conditions, wherein the target air–fuel ratio is a stoichiometric air–fuel ratio, and wherein the catalytic converter is a three-way catalytic converter configured to simultaneously convert nitrogen oxides, carbon monoxide, and unburned hydrocarbons present in the combusted gases.

7. The system as claimed in claim 1, wherein the adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor, and wherein the engine control unit commands the ignition system to retard the ignition timing without reliance on a knock sensor.

8. The system as claimed in claim 1, wherein the adaptive fuel correction value compensates for fuel composition variability across a plurality of gaseous fuel types including at least two of: compressed natural gas, liquefied natural gas, biogas, compressed biogas, hydrogen-enriched natural gas, and mixtures thereof, and wherein the adaptive fuel correction value further compensates for progressive fuel injector flow drift occurring over a useful life of the internal combustion engine.

9. A method for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, the method comprising: commanding at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine; receiving an air–fuel ratio signal from an exhaust gas sensor positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine; deriving an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio; applying the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio; determining whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold; and upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, commanding an ignition system to retard an ignition timing relative to a base ignition timing.

10. The method as claimed in claim 9, further comprising: acquiring a plurality of engine operating parameters including at least engine speed and engine load; and storing the adaptive fuel correction value in a two-dimensional adaptive fuel learning map indexed by the engine speed and the engine load, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map.

11. The method as claimed in claim 9, further comprising: storing the adaptive fuel correction value in a non-volatile memory; and applying the stored adaptive fuel correction value to the fuel injection commands upon a subsequent engine start of the internal combustion engine to reduce transient deviation between the received air–fuel ratio signal and the target air–fuel ratio.

12. The method as claimed in claim 9, wherein different ranges of the magnitude of the adaptive fuel correction value correspond to different inferred fuel quality states, and wherein, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the ignition timing is retarded by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold.

13. The method as claimed in claim 9, further comprising: generating a base fuel injection command based on a feed-forward fuel map and at least engine speed and engine load of the internal combustion engine prior to commanding the at least one gaseous fuel injector; and updating the feed-forward fuel map with the adaptive fuel correction value for use in generating subsequent base fuel injection commands; wherein the method is continuously and cyclically executed during operation of the internal combustion engine.

14. An engine control unit for controlling an internal combustion engine operating on gaseous fuel, the engine control unit comprising: one or more processing units; and a memory unit communicatively coupled to the one or more processing units, the memory unit storing machine-readable instructions that, when executed by the one or more processing units, cause the engine control unit to: receive an air–fuel ratio signal from an exhaust gas sensor indicative of an air–fuel ratio of combusted gases in the internal combustion engine; derive an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio; output a fuel injection command adjusted by the adaptive fuel correction value to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio; determine whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold; and upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, output an ignition command to retard an ignition timing relative to a base ignition timing.

15. The engine control unit as claimed in claim 14, wherein the memory unit further stores a two-dimensional adaptive fuel learning map indexed by engine speed and engine load of the internal combustion engine, and wherein the machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to: store the adaptive fuel correction value in the two-dimensional adaptive fuel learning map, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map; and retain the stored adaptive fuel correction value in the memory unit across successive engine start and engine stop cycles of the internal combustion engine; wherein the adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor.

Description:DESCRIPTION
FIELD OF PRESENT INVENTION
The present invention relates to the field of engine control systems for internal combustion engines. More specifically, the present invention pertains to systems, methods, and engine control units for adaptive fuel injection and ignition timing control in internal combustion engines configured for operation on gaseous fuel, including but not limited to compressed natural gas (CNG), liquefied natural gas (LNG), biogas, compressed biogas (CBG), hydrogen-enriched natural gas (HCNG), renewable natural gas (RNG), and mixtures thereof.
BACKGROUND
Internal combustion engines configured for operation on gaseous fuel are increasingly employed as alternatives to internal combustion engines configured for operation on conventional liquid fuels such as gasoline and diesel. Gaseous fuels, including compressed natural gas (CNG), liquefied natural gas (LNG), biogas, compressed biogas (CBG), hydrogen-enriched natural gas (HCNG), and mixtures thereof, offer potential advantages in reducing carbon emissions and improving energy security. In internal combustion engines configured for operation on gaseous fuel, fuel injection is controlled by an engine control unit that generates a base fuel injection command based on a feed-forward fuel map. The feed-forward fuel map is a pre-calibrated look-up table that provides a base fuel injection quantity as a function of engine operating parameters, including at least engine speed and engine load, and the feed-forward fuel map assumes a nominal or reference fuel composition. An exhaust gas sensor, positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine, provides feedback indicative of an air–fuel ratio of combusted gases, and the engine control unit uses the feedback from the exhaust gas sensor for closed-loop regulation of the air–fuel ratio. A catalytic converter, and more particularly a three-way catalytic converter, is provided in the exhaust system of the internal combustion engine to simultaneously convert nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC) present in the combusted gases. The three-way catalytic converter achieves high conversion efficiency for all three regulated exhaust gas constituents only when the air–fuel ratio of the combusted gases is maintained within a narrow range around a stoichiometric air–fuel ratio.
Unlike liquid fuels such as gasoline and diesel, whose chemical composition is controlled through standardized refining and blending processes, gaseous fuel supplied for vehicular applications does not undergo a uniform or centralized refining process to achieve a consistent and repeatable composition. The composition of gaseous fuel is dependent on the source and supply chain of the gaseous fuel, including geological origin, extraction method, processing level, transportation, and blending practices. Gaseous fuel sourced from different geographical regions or suppliers may vary in methane concentration and may contain varying proportions of higher hydrocarbons such as ethane, propane, and butane, as well as inert or diluent gases including carbon dioxide and nitrogen. This variation in fuel composition directly affects fuel properties including lower heating value, fuel calorific value, Wobbe index, stoichiometric air–fuel ratio, laminar flame speed, and ignition characteristics. Although applicable standards specify compositional limits for gaseous fuel, for example methane content equal to or greater than 90%, real-world commercial gaseous fuel frequently deviates from these nominal specifications. This variability has been further amplified by regulatory developments mandating blending of compressed biogas (CBG) in compressed natural gas (CNG) supply, wherein compressed biogas is produced from diverse biological feedstocks and production pathways and exhibits significant variation in calorific value, inert content, and combustion characteristics. The combined effect of multi-source gaseous fuel supply and mandated compressed biogas blending substantially increases real-world fuel composition variability encountered by internal combustion engines configured for operation on gaseous fuel.
As a result of fuel composition variability, when the actual fuel composition deviates from the nominal or reference fuel composition assumed in the feed-forward fuel map, the base fuel injection command generated by the engine control unit becomes inherently inaccurate, leading to incorrect fuel mass delivery per combustion cycle. This causes improper air–fuel ratio control, increased combustion variability, degraded drivability, reduced fuel economy, and elevated tailpipe emissions. In gaseous fuel–fuelled internal combustion engines, even small deviations in injected fuel quantity, on the order of approximately one percent, can result in disproportionately large air–fuel ratio deviations due to the sensitivity of gaseous fuel combustion to variations in fuel calorific value and stoichiometric air–fuel ratio. These air–fuel ratio deviations have a direct and severe impact on exhaust after-treatment performance, particularly in engines equipped with a three-way catalytic converter. The three-way catalytic converter operates efficiently only within a narrow stoichiometric window, and even slight lean or rich deviations cause a sharp deterioration in conversion efficiency, leading to increased emissions of unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). This challenge is further exacerbated by the disparity between laboratory-based emission testing and real-world driving emissions. Laboratory tests are conducted under controlled conditions using stabilized fuels and fixed ambient parameters. In contrast, real-world driving involves uncontrolled variables such as commercial fuel variability, altitude changes, cold and hot ambient conditions, and humidity variation. The interaction of these factors with slow, reactive air–fuel ratio correction can non-linearly amplify air–fuel ratio errors and emission excursions under real driving emission conditions.
In addition to fuel composition variability, manufacturing tolerances, aging, and deterioration of fuel system components introduce further uncertainty in fuel delivery accuracy over a useful life of the internal combustion engine. Components such as pressure regulators and, in particular, gaseous fuel injectors exhibit variability at manufacture and progressive degradation during field operation. Fuel injector flow rates may increase or decrease over time due to deposits, contamination, wear, or changes in opening dynamics of the gaseous fuel injector. When fuel injector flow drift due to aging is combined with fuel composition variability, fuel delivery errors become cumulative and further degrade the accuracy of the base fuel injection command. This issue is particularly relevant under real driving emission (RDE) regulations with useful vehicle life requirements, which mandate emission compliance throughout a defined useful life of the vehicle. While new vehicles may meet emission limits, older vehicles experiencing fuel injector flow drift, pressure regulator drift, and cumulative fuel composition variability may fail to comply under real-world conditions. Further, if the combustion quality of the gaseous fuel becomes significantly inferior, the internal combustion engine may continue to operate with such inferior gaseous fuel, leading to abnormal combustion phenomena including knock and detonation, which can cause engine damage and constitute a safety concern.
Beyond emissions compliance, fuel composition variability drives system-level over-engineering. To compensate for air–fuel ratio uncertainty and emission excursions, manufacturers are forced to adopt larger catalytic converters with higher platinum group metal (PGM) loading. Platinum group metals are among the most expensive and supply-constrained materials. Increased platinum group metal loading leads to higher vehicle cost and increased material dependence, while still failing to address the root cause of emission variability. Accordingly, there is a need for a system, a method, and an engine control unit capable of maintaining precise air–fuel ratio control, preserving high catalytic converter conversion efficiency, and ensuring consistent real-world emission compliance throughout the useful life of the vehicle, despite unknown fuel composition variability and progressive fuel system component degradation, without reliance on direct fuel composition sensing.
Some conventional engine control units employ long-term fuel trim values or correction factors, which are stored as single global correction values or limited-range correction factors, to compensate for persistent offsets in fuel delivery. In some conventional systems, knock sensors are employed to detect abnormal combustion events such as knock or detonation, and the engine control unit adjusts ignition timing based on knock sensor feedback to suppress knock and protect engine hardware.
Single global fuel trim values or limited-range correction factors used in conventional engine control units do not account for non-linear and operating-point-dependent fuel delivery deviations. Fuel delivery deviations arising from fuel injector flow drift, injector opening dynamics, or pressure regulation errors may result in disproportionately different fueling errors at different engine speeds and engine loads. A single global correction value cannot capture such non-linear, region-dependent deviations across the entire operating range of the internal combustion engine. Additionally, conventional engine control units do not derive or infer information about fuel quality or combustion characteristics from the magnitude of fuel correction values. Conventional engine control units do not autonomously adjust ignition timing based on the magnitude of learned fuel correction values to mitigate abnormal combustion risks arising from inferior fuel quality. In conventional systems that employ knock sensors for ignition timing control, the knock sensor detects abnormal combustion only after the abnormal combustion event has already occurred, and the engine control unit responds reactively rather than pre-emptively.
US 9,926,864 B2 discloses a control system for an internal combustion engine that can use a plurality of kinds of fuel including compressed natural gas, wherein an electronic control unit determines whether properties of the compressed natural gas need to be learned, executes a learning processing to learn the properties of the compressed natural gas using an air-fuel ratio feedback correction value, and prohibits a changeover from the compressed natural gas to another fuel while the learning processing is in progress. This reference describes an electronic control unit which learns a single inert gas concentration learning value that corrects the theoretical air-fuel ratio globally based on the magnitude of the air-fuel ratio feedback correction value, and the learning processing is directed to preventing engine stalls during fuel changeover events.
US 7,958,866 B2 discloses a method and system for closed loop lambda control of a gaseous fuelled internal combustion engine, wherein an engine control module introduces an inner control loop to the lambda control based on the pressure of the gaseous fuel downstream of a fuel control valve and upstream of a carburetor relative to the pressure of the air at the inlet of the carburetor, and introduces operating point based dynamic parameter scheduling in the lambda feedback control loop. The dynamic parameters in the lambda control are scheduled as a function of mass flow through the engine to account for operating point related variation in mixing dynamics and transport time delays, and the method requires a fuel delta pressure sensor as part of the inner control loop.
US 11,840,971 B2 discloses systems, methods, and apparatus for operation of dual fuel engines, wherein an electronic controller determines a substitution parameter for substitution of gaseous fuel for liquid fuel based upon an engine load value, an intake manifold temperature value, and a parameter representative of gaseous fuel quality, and iteratively increases the parameter representative of the gaseous fuel quality and the substitution parameter until engine knock is detected. The system includes a knock determination module structured to determine a current knock value for the gaseous fuel in the dual fuel engine and a knock adjustment module structured to determine an adjusted substitution rate based on comparing the expected knock value and the current knock value.
US 2009/0107441 A1 discloses an adaptive fuel control strategy for engine starting, wherein a control system varies an amount of fuel injected into a combustion chamber during an engine start based on a speed response of the engine during a previous engine run-up from rest and a change in an amount of fuel stored in a fuel storage tank before the engine start. The control system in this reference computes an adaptive correction offset stored in keep-alive memory for use in a subsequent engine start, and adjusts both a fuel injection amount and a spark timing during the engine starting phase to compensate for fuel volatility variations.
US 5,267,548 A discloses a method for adapted precontrol and feedback control of the air/fuel mixtures supplied to two fuel-metering devices of an internal combustion engine having two separate exhaust-gas channels with a lambda probe and a catalytic converter in each channel, wherein a common value of a precontrol manipulated variable and a common lambda desired value are determined for both fuel-metering devices, and values of precontrol adaptation variables are determined separately for each fuel-metering device based on values of a feedback control manipulated variable. The precontrol adaptation compensates for individual disturbances such as different air leakage rates and different through-flow rates of the fuel-metering devices across two cylinder banks, and the adaptation values are superposed on the common precontrol value.
None of the above cited references describes an adaptive fuel injection and ignition control in which an adaptive fuel correction value is derived from air–fuel ratio feedback, stored in a two-dimensional adaptive fuel learning map indexed by engine speed and engine load for operating-region-specific compensation across the entire engine operating range, and used to autonomously command ignition timing retard based on the magnitude of the adaptive fuel correction value exceeding a predefined threshold indicative of inferior fuel quality. Therefore, there is a need for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, and capable of compensating for fuel composition variability and fuel injector flow drift across the entire operating range of the internal combustion engine, without reliance on direct fuel composition sensing, and further capable of autonomously adjusting ignition timing when a magnitude of an adaptive fuel correction value exceeds a predefined threshold indicative of inferior fuel quality or abnormal combustion characteristics.
SUMMARY
The object of the present invention is achieved by a system for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel. The system comprises an engine control unit communicatively coupled to at least one gaseous fuel injector, an ignition system, and an exhaust gas sensor positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine. The engine control unit is configured to acquire a plurality of engine operating parameters including at least engine speed and engine load. The engine control unit is configured to generate a base fuel injection command based on a feed-forward fuel map and the acquired engine operating parameters. The engine control unit is configured to command the at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine based on the base fuel injection command. The engine control unit is configured to receive an air–fuel ratio signal from the exhaust gas sensor indicative of an air–fuel ratio of combusted gases. The engine control unit is configured to compute a deviation between the received air–fuel ratio signal and a target air–fuel ratio. The engine control unit is configured to derive an adaptive fuel correction value based on the computed deviation. The engine control unit is configured to apply the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio. The engine control unit is configured to determine whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold. Upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the engine control unit is configured to command the ignition system to retard an ignition timing relative to a base ignition timing. This arrangement enables the engine control unit to maintain the air–fuel ratio within a narrow stoichiometric window required for high conversion efficiency of the catalytic converter across varying fuel compositions and fuel system conditions, while also pre-emptively mitigating abnormal combustion risks when the magnitude of the adaptive fuel correction value indicates inferior fuel quality, without reliance on a direct fuel composition sensor or a knock sensor.
In one or more embodiments, the engine control unit is further configured to store the adaptive fuel correction value in a two-dimensional adaptive fuel learning map indexed by the engine speed and the engine load. Herein, the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map. This arrangement enables the engine control unit to capture and compensate for non-linear and operating-point-dependent fuel delivery deviations that vary across different combinations of engine speed and engine load, thereby providing more accurate air–fuel ratio control across the entire operating range of the internal combustion engine compared to a single uniform correction value.
In one or more embodiments, the engine control unit is configured to derive the adaptive fuel correction value based on the computed deviation in combination with historical injector opening duration data associated with the at least one gaseous fuel injector. Herein, the engine control unit derives the adaptive fuel correction value when predefined fuel learning conditions are satisfied. The predefined fuel learning conditions include at least one of steady-state operation of the internal combustion engine, absence of knock in the internal combustion engine, validity of sensor signals associated with the internal combustion engine, and operation of the internal combustion engine within predefined temperature ranges. The use of the historical injector opening duration data in combination with the computed deviation enables the engine control unit to derive an adaptive fuel correction value that accounts for both fuel composition variability and fuel injector flow drift, and the predefined fuel learning conditions ensure that the adaptive fuel correction value is derived under stable and representative operating conditions such that the derived adaptive fuel correction value accurately reflects persistent fuel delivery deviations.
In one or more embodiments, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the engine control unit commands the ignition system to retard the ignition timing by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold. The proportional relationship between the ignition timing retard and the difference between the magnitude of the adaptive fuel correction value and the predefined threshold provides a graduated ignition timing correction that is commensurate with the severity of the inferred fuel quality degradation, thereby ensuring sufficient mitigation of abnormal combustion risks while minimizing unnecessary reduction in engine performance and thermal efficiency.
In one or more embodiments, the system further comprises a non-volatile memory communicatively coupled to the engine control unit. Herein, the engine control unit is configured to store the adaptive fuel correction value in the non-volatile memory. The engine control unit is configured to retain the stored adaptive fuel correction value in the non-volatile memory across successive engine start and engine stop cycles of the internal combustion engine. The engine control unit is configured to apply the stored adaptive fuel correction value to the fuel injection commands upon a subsequent engine start to reduce transient deviation between the received air–fuel ratio signal and the target air–fuel ratio. The retention of the stored adaptive fuel correction value across successive engine start and engine stop cycles eliminates the need for a new learning cycle upon each engine start, thereby reducing transient air–fuel ratio deviations and emission excursions during engine start and enabling immediate stabilization of the air–fuel ratio from the first combustion cycle following engine start.
In one or more embodiments, the exhaust gas sensor is a wideband-type lambda sensor configured to measure the air–fuel ratio of the combusted gases over a range extending from lean conditions to rich conditions. Herein, the target air–fuel ratio is a stoichiometric air–fuel ratio. Further, herein, the catalytic converter is a three-way catalytic converter configured to simultaneously convert nitrogen oxides, carbon monoxide, and unburned hydrocarbons present in the combusted gases. The wideband-type lambda sensor provides the engine control unit with an accurate air–fuel ratio signal over a wide operating range, enabling the engine control unit to derive the adaptive fuel correction value even when the air–fuel ratio deviates significantly from the stoichiometric condition, and the maintenance of the stoichiometric air–fuel ratio ensures that the three-way catalytic converter achieves sustained high conversion efficiency for all three regulated exhaust gas constituents.
In one or more embodiments, the adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor. Herein, the engine control unit commands the ignition system to retard the ignition timing without reliance on a knock sensor. This arrangement eliminates the need for costly and impractical direct fuel composition sensors and eliminates reliance on knock sensors for ignition timing correction, thereby reducing system complexity and component cost while enabling pre-emptive ignition timing adjustment based on the magnitude of the adaptive fuel correction value rather than reactive adjustment based on detection of an already-occurred knock event.
In one or more embodiments, the adaptive fuel correction value compensates for fuel composition variability across a plurality of gaseous fuel types including at least two of compressed natural gas, liquefied natural gas, biogas, compressed biogas, hydrogen-enriched natural gas, and mixtures thereof. Herein, the adaptive fuel correction value further compensates for progressive fuel injector flow drift occurring over a useful life of the internal combustion engine. This arrangement enables the internal combustion engine to operate on different gaseous fuel types and mixtures thereof without requiring identification of the specific gaseous fuel type or recalibration of the engine control unit, and the continuous compensation for progressive fuel injector flow drift ensures that the fuel injection commands remain accurate over the useful life of the internal combustion engine without requiring injector replacement or recalibration.
The object of the present invention is also achieved by a method for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel. The method comprises commanding at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine. The method further comprises receiving an air–fuel ratio signal from an exhaust gas sensor positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine. The method further comprises deriving an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio. The method further comprises applying the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio. The method further comprises determining whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold. Upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the method further comprises commanding an ignition system to retard an ignition timing relative to a base ignition timing. This method enables real-time identification, compensation, and adaptation of the fuel injection quantity and the ignition timing in response to fuel composition variability and fuel system degradation, without reliance on direct fuel composition sensing, thereby maintaining the air–fuel ratio within the narrow stoichiometric window and pre-emptively mitigating abnormal combustion risks throughout the operation of the internal combustion engine.
In one or more embodiments, the method further comprises acquiring a plurality of engine operating parameters including at least engine speed and engine load. The method further comprises storing the adaptive fuel correction value in a two-dimensional adaptive fuel learning map indexed by the engine speed and the engine load. Herein, the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map. The storage of the adaptive fuel correction value in the two-dimensional adaptive fuel learning map with independent updating for each region enables the method to account for the non-linear relationship between fuel delivery deviation and engine operating point, thereby providing operating-region-specific compensation that improves the accuracy of the air–fuel ratio control across the entire operating range.
In one or more embodiments, the method further comprises storing the adaptive fuel correction value in a non-volatile memory. The method further comprises applying the stored adaptive fuel correction value to the fuel injection commands upon a subsequent engine start of the internal combustion engine to reduce transient deviation between the received air–fuel ratio signal and the target air–fuel ratio. The storage of the adaptive fuel correction value in the non-volatile memory and the application of the stored adaptive fuel correction value upon a subsequent engine start enable the method to provide immediate air–fuel ratio stabilization without requiring a new learning cycle, thereby reducing transient emission excursions during engine start.
In one or more embodiments, different ranges of the magnitude of the adaptive fuel correction value correspond to different inferred fuel quality states. Herein, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the ignition timing is retarded by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold. The classification of fuel quality based on different ranges of the magnitude of the adaptive fuel correction value enables the method to infer the fuel quality state without use of a direct fuel composition sensor, and the proportional ignition timing retard ensures that the degree of ignition timing correction corresponds to the severity of the inferred fuel quality degradation.
In one or more embodiments, the method further comprises generating a base fuel injection command based on a feed-forward fuel map and at least engine speed and engine load of the internal combustion engine prior to commanding the at least one gaseous fuel injector. The method further comprises updating the feed-forward fuel map with the adaptive fuel correction value for use in generating subsequent base fuel injection commands. Herein, the method is continuously and cyclically executed during operation of the internal combustion engine. The updating of the feed-forward fuel map with the adaptive fuel correction value progressively refines the base fuel injection command to reflect the actual fuel composition and fuel injector flow characteristics, reducing the magnitude of closed-loop correction required in subsequent engine control cycles, and the continuous and cyclic execution of the method ensures that the adaptive fuel injection and ignition control responds to changes in fuel composition and fuel system conditions throughout the operation of the internal combustion engine.
The object of the present invention is further achieved by an engine control unit for controlling an internal combustion engine operating on gaseous fuel. The engine control unit comprises one or more processing units and a memory unit communicatively coupled to the one or more processing units. The memory unit stores machine-readable instructions that, when executed by the one or more processing units, cause the engine control unit to receive an air–fuel ratio signal from an exhaust gas sensor indicative of an air–fuel ratio of combusted gases in the internal combustion engine. The machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to derive an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio. The machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to output a fuel injection command adjusted by the adaptive fuel correction value to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio. The machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to determine whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold. Upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to output an ignition command to retard an ignition timing relative to a base ignition timing. This arrangement enables the engine control unit to autonomously perform adaptive fuel injection and ignition control by executing the machine-readable instructions stored in the memory unit, without requiring external computation, direct fuel composition sensing, or knock sensing, thereby providing a self-contained and production-viable control architecture for internal combustion engines operating on gaseous fuel with variable fuel composition.
In one or more embodiments, the memory unit further stores a two-dimensional adaptive fuel learning map indexed by engine speed and engine load of the internal combustion engine. Herein, the machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to store the adaptive fuel correction value in the two-dimensional adaptive fuel learning map, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map. The machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to retain the stored adaptive fuel correction value in the memory unit across successive engine start and engine stop cycles of the internal combustion engine. Herein, the adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor. This arrangement enables the engine control unit to maintain operating-region-specific fuel correction values that persist across engine start and engine stop cycles and that inherently compensate for fuel composition variability and fuel injector flow drift without requiring direct fuel composition measurement, thereby providing sustained air–fuel ratio accuracy and emission compliance over the useful life of the internal combustion engine.
Still, other aspects, features, and advantages of the invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the invention. The invention is also capable of other and different embodiments, and its several details may be modified in various obvious respects, all without departing from the scope of the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF DRAWINGS
A more complete appreciation of the present invention and many of the attendant aspects thereof will be readily obtained as the same becomes better understood by reference to the following description when considered in connection with the accompanying drawings:
FIG. 1 is a schematic representation of an internal combustion engine system configured for operation on gaseous fuel, in accordance with one or more embodiments of the present invention;
FIG. 2 is a block diagram representation of an engine control unit and associated components for adaptive fuel injection and ignition control in the internal combustion engine, in accordance with one or more embodiments of the present invention;
FIG. 3 is a flowchart of a method for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, in accordance with one or more embodiments of the present invention;
FIG. 4 is a detailed flowchart of a method for adaptive fuel injection and ignition control depicting data acquisition, computation, fuel learning, and ignition timing correction steps, in accordance with one or more embodiments of the present invention; and
FIG. 5 is a representative graph illustrating catalytic conversion efficiency of a three-way catalytic converter as a function of a pre-catalyst air–fuel ratio, in accordance with one or more embodiments of the present invention.
DETAILED DESCRIPTION
Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details.
Examples of a system, a method, and an engine control unit for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel are disclosed herein. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It is apparent, however, to one skilled in the art that the embodiments of the invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention.
For purposes of the present invention, the term “gaseous fuel” refers to fuel in a gaseous state suitable for use in an internal combustion engine, including but not limited to natural gas, compressed natural gas (CNG), liquefied natural gas (LNG), biogas, compressed biogas (CBG), hydrogen-enriched natural gas (HCNG), renewable natural gas (RNG), and mixtures thereof. Gaseous fuel may vary in composition depending on the source, supply chain, processing level, and blending practices, and such variation is referred to herein as “fuel composition variability.”
For purposes of the present invention, the term “feed-forward fuel map” refers to a pre-calibrated look-up table or map stored in the engine control unit that provides a base fuel injection quantity as a function of engine operating parameters, including at least engine speed and engine load. The feed-forward fuel map is calibrated assuming a nominal or reference fuel composition and nominal fuel injector flow characteristics.
For purposes of the present invention, the term “adaptive fuel correction value” refers to a correction value derived by the engine control unit based on a deviation between a received air–fuel ratio signal and a target air–fuel ratio. The adaptive fuel correction value is applied to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio. The adaptive fuel correction value inherently captures variations in fuel composition, fuel calorific value, fuel injector flow characteristics, and pressure regulation deviation, without requiring direct measurement of fuel composition.
For purposes of the present invention, the term “two-dimensional adaptive fuel learning map” refers to a map stored in the engine control unit and indexed by engine speed and engine load. The two-dimensional adaptive fuel learning map stores adaptive fuel correction values independently for each region of the engine operating range, wherein each region corresponds to a distinct combination of engine speed and engine load. The two-dimensional adaptive fuel learning map enables operating-region-specific correction rather than a single uniform correction value applied across the entire operating range of the internal combustion engine.
For purposes of the present invention, the term “predefined threshold” refers to a predetermined value of the magnitude of the adaptive fuel correction value, exceedance of which is indicative of one or more of inferior fuel quality, abnormal combustion characteristics, reduced combustion stability, or conditions requiring adjustment of ignition timing. The predefined threshold is calibrated to distinguish normal fuel composition variations from conditions that warrant ignition timing correction for protection of engine hardware and maintenance of combustion stability.
For purposes of the present invention, the term “base ignition timing” refers to an ignition timing value determined from a feed-forward ignition timing map stored in the engine control unit, the feed-forward ignition timing map being calibrated as a function of engine operating parameters including at least engine speed and engine load, assuming a nominal or reference fuel composition.
For purposes of the present invention, the term “stoichiometric air–fuel ratio” refers to the air–fuel ratio at which the quantity of air is exactly sufficient for complete combustion of the quantity of gaseous fuel, corresponding to a lambda value of approximately 1.0. The stoichiometric air–fuel ratio varies depending on the composition of the gaseous fuel.
For purposes of the present invention, the term “non-volatile memory” refers to a memory element that retains stored data across power-off and power-on cycles of the engine control unit, such that data stored in the non-volatile memory is preserved when electrical power is removed from the engine control unit and is available when electrical power is restored to the engine control unit.
For purposes of the present invention, the term “predefined fuel learning conditions” refers to one or more conditions under which the engine control unit derives or updates the adaptive fuel correction value. The predefined fuel learning conditions include at least one of steady-state operation of the internal combustion engine, absence of knock in the internal combustion engine, validity of sensor signals associated with the internal combustion engine, and operation of the internal combustion engine within predefined temperature ranges.
For purposes of the present invention, the term “historical injector opening duration data” refers to data representing past injector opening durations or fuel injection pulse widths recorded by the engine control unit during prior operation of the internal combustion engine. The historical injector opening duration data is associated with the at least one gaseous fuel injector and is used by the engine control unit in combination with the computed deviation to derive the adaptive fuel correction value.
For purposes of the present invention, the term “inferred fuel quality states” refers to classifications of fuel quality derived by the engine control unit based on the magnitude of the adaptive fuel correction value, without direct measurement of fuel composition. Different ranges of the magnitude of the adaptive fuel correction value correspond to different inferred fuel quality states, wherein a higher magnitude of the adaptive fuel correction value indicates a greater deviation of the actual fuel composition from the nominal or reference fuel composition assumed in the feed-forward fuel map.
Referring to FIG. 1, illustrated is a schematic representation of an internal combustion engine system 100 configured for operation on gaseous fuel, in accordance with one or more embodiments of the present invention. The internal combustion engine system 100 is, more particularly, a spark-ignition type internal combustion engine configured for operation on gaseous fuel, including but not limited to natural gas, compressed natural gas (CNG), liquefied natural gas (LNG), compressed biogas (CBG), renewable natural gas (RNG), hydrogen-enriched natural gas (HCNG), and mixtures thereof. FIG. 1 is illustrated in a single-cylinder configuration for clarity of explanation. However, it shall be understood that the disclosed architecture, components, subsystems, and control methodologies are not limited to single-cylinder configurations and are equally applicable to multi-cylinder configurations, including inline, V-type, opposed, or other known configurations, without departing from the scope of the invention.
The internal combustion engine system 100 comprises a cylinder block 108, a cylinder head 102, and a piston 104, which together define a primary mechanical structure of the internal combustion engine. The piston 104 is reciprocally disposed within the cylinder block 108. A volume defined between the piston 104 and the cylinder head 102 forms a combustion chamber 106. The piston 104 is operatively connected to a crankshaft 110 through a connecting rod 112, such that reciprocating motion of the piston 104 is converted into rotational motion of the crankshaft 110 to generate mechanical output. During operation, the piston 104 reciprocates within the cylinder block 108 to induct an air–gaseous fuel mixture into the combustion chamber 106, compress the air–gaseous fuel mixture, and transmit combustion forces generated upon ignition to the crankshaft 110 via the connecting rod 112.
The cylinder head 102 accommodates an intake valve 114, an exhaust valve 116, and a spark plug 118. The intake valve 114 is configured to control the flow of intake charge into the combustion chamber 106 during an intake stroke of the piston 104. The exhaust valve 116 is configured to control the discharge of combusted gases from the combustion chamber 106 during an exhaust stroke of the piston 104. The spark plug 118 is positioned in the cylinder head 102 and extends into the combustion chamber 106 to initiate ignition of the compressed air–gaseous fuel mixture. Engine operating parameters, including engine speed and engine load, are regulated in response to an operator input via an accelerator pedal 156, which is interpreted by an engine control unit 146.
The flow of gases into and out of the combustion chamber 106 is controlled by a valve train mechanism. The valve train mechanism comprises the intake valve 114, the exhaust valve 116, and a camshaft 168 synchronized with rotation of the crankshaft 110. A crankshaft position sensor 152 is provided to detect the engine speed and a top dead center position of the piston 104 within the cylinder block 108. A camshaft position sensor 164 is provided to monitor a camshaft angular position of the camshaft 168. The signals from the crankshaft position sensor 152 and the camshaft position sensor 164 are communicated to the engine control unit 146 and are utilized by the engine control unit 146 to achieve accurate synchronization of fuel injection events and ignition events with respect to the position of the piston 104 within the cylinder block 108.
A gaseous fuel supply subsystem is provided for storing, conditioning, and metering gaseous fuel to the internal combustion engine. Gaseous fuel is stored in a high-pressure storage cylinder 172, which in the case of compressed natural gas (CNG) stores the gaseous fuel at pressures in the range of approximately 200 to 250 bar. The gaseous fuel is conveyed from the high-pressure storage cylinder 172 through reinforced fuel lines to a high-pressure fuel regulator 170. The high-pressure fuel regulator 170 is configured to reduce the storage pressure of the gaseous fuel to an intermediate pressure level suitable for downstream handling, metering, and safe operation. The gaseous fuel subsequently flows from the high-pressure fuel regulator 170 to a fuel rail 150 through one or more additional pressure-conditioning stages. A fuel rail pressure and temperature sensor 166 is mounted on the fuel rail 150 to continuously monitor the pressure and temperature of the gaseous fuel within the fuel rail 150. The signals from the fuel rail pressure and temperature sensor 166 are communicated to the engine control unit 146 for use in determining the density and flow characteristics of the gaseous fuel being supplied to the at least one gaseous fuel injector 128.
At least one gaseous fuel injector 128 is provided and is fluidly coupled to the fuel rail 150 and is positioned to inject metered gaseous fuel into an intake port 124 of the internal combustion engine. The at least one gaseous fuel injector 128 is an electronically controlled injector that receives a fuel injection command from the engine control unit 146, the fuel injection command defining an injector opening duration or fuel injection pulse width that determines the quantity of gaseous fuel injected per combustion cycle. By injecting gaseous fuel into the intake port 124, the at least one gaseous fuel injector 128 enables mixing of the gaseous fuel with intake air prior to entry of the air–gaseous fuel mixture into the combustion chamber 106 via the intake valve 114. It shall be understood that in alternative embodiments, the at least one gaseous fuel injector 128 may be configured for direct injection of gaseous fuel into the combustion chamber 106, without departing from the scope of the invention. The at least one gaseous fuel injector 128 is communicatively coupled to the engine control unit 146 such that the engine control unit 146 controls the timing and duration of each fuel injection event.
Clean air required for combustion is supplied through an air intake system 144. The air intake system 144 comprises an air filter 142, a compressor 138, an intercooler 132, an electronic throttle body 130, and an intake manifold 126. The air filter 142 is configured to remove particulate matter and contaminants from ambient air entering the air intake system 144. The compressor 138 cooperates with a turbine 136 to form a turbocharger assembly, wherein the turbine 136 is driven by energy of exhaust gases and is mechanically coupled to the compressor 138 via a rotor shaft 140. The compressor 138 compresses the intake air to increase the air pressure and density supplied to the internal combustion engine, thereby improving volumetric efficiency and engine performance. The intercooler 132 is positioned downstream of the compressor 138 and is configured to reduce the temperature of the compressed intake air before the compressed intake air enters the electronic throttle body 130 and the intake manifold 126. The electronic throttle body 130 is configured to regulate the quantity of intake air admitted to the intake manifold 126 based on a command from the engine control unit 146. The intake manifold 126 distributes the intake air to the intake port 124 of each cylinder of the internal combustion engine.
One or more intake air monitoring sensors are provided for closed-loop air management. A boost pressure and temperature sensor 134 is configured to measure boosted intake air conditions, including pressure and temperature of the intake air, upstream of the electronic throttle body 130. A manifold air pressure and temperature sensor 154 is configured to monitor the pressure and the temperature of the intake charge within the intake manifold 126. The signals from the boost pressure and temperature sensor 134 and the manifold air pressure and temperature sensor 154 are communicated to the engine control unit 146 for real-time regulation of airflow, boost pressure, air–fuel ratio, combustion stability, and engine protection functions.
An ignition system 174 is provided for initiating combustion of the compressed air–gaseous fuel mixture within the combustion chamber 106. The ignition system 174 comprises an ignition coil 148 and the spark plug 118. The ignition coil 148 generates a high-voltage electrical signal that is supplied to the spark plug 118. The spark plug 118 produces a spark discharge at a commanded ignition timing to initiate combustion of the compressed air–gaseous fuel mixture near the end of a compression stroke of the piston 104. The ignition timing, which defines the point in time during the engine cycle at which the spark plug 118 produces the spark discharge, is commanded by the engine control unit 146 through the ignition coil 148. In view of the higher ignition temperature and comparatively slower flame propagation characteristics associated with gaseous fuels such as compressed natural gas, the ignition timing may be selectively advanced relative to liquid-fuel operation to enhance combustion stability, thermal efficiency, and torque output. The ignition system 174 is communicatively coupled to the engine control unit 146, and the engine control unit 146 determines and commands the ignition timing for each combustion cycle based on the engine operating parameters and, when applicable, based on the adaptive fuel correction value as described herein.
Combustion exhaust gases 178 are discharged from the combustion chamber 106 through an exhaust system 176. The exhaust system 176 comprises an exhaust port 120, an exhaust manifold 122, the turbine 136, and an after-treatment system 180. The exhaust port 120 is formed in the cylinder head 102 and connects the combustion chamber 106 to the exhaust manifold 122. The exhaust manifold 122 collects the combustion exhaust gases 178 from the exhaust port 120 of each cylinder and directs the combustion exhaust gases 178 to the turbine 136. The turbine 136, which forms part of the turbocharger assembly together with the compressor 138 and the rotor shaft 140, extracts energy from the combustion exhaust gases 178 to drive the compressor 138.
The after-treatment system 180 of the exhaust system 176 comprises a catalytic converter 160, an exhaust gas sensor 158 positioned upstream of the catalytic converter 160, and a post-catalyst lambda sensor 162 positioned downstream of the catalytic converter 160. The exhaust gas sensor 158 is positioned upstream of the catalytic converter 160 in the exhaust system 176 and is configured to provide an air–fuel ratio signal indicative of the air–fuel ratio of the combusted gases flowing through the exhaust system 176. In one or more embodiments, the exhaust gas sensor 158 is implemented as a wideband-type lambda sensor, also referred to as a pre-catalyst lambda sensor. The wideband-type lambda sensor is configured to measure the air–fuel ratio of the combusted gases over a range extending from lean conditions to rich conditions, for example from approximately lambda 0.65 to lambda 10. The air–fuel ratio signal from the exhaust gas sensor 158 is communicated to the engine control unit 146, and the engine control unit 146 utilizes the air–fuel ratio signal for closed-loop fuel control and for deriving the adaptive fuel correction value as described herein.
In present embodiments, the catalytic converter 160 is implemented as a three-way catalytic converter. The three-way catalytic converter is so named because the three-way catalytic converter is configured to simultaneously convert three primary regulated exhaust gas constituents, namely nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC), into less harmful constituents. The catalytic converter 160 typically comprises a high-surface-area ceramic or metallic substrate formed in a honeycomb structure and coated with a catalytic washcoat containing precious metal catalysts such as platinum (Pt), palladium (Pd), and rhodium (Rh). These catalytic materials promote oxidation and reduction reactions when the composition of the combustion exhaust gases 178 is maintained within a narrow stoichiometric air–fuel ratio window. During operation, the catalytic converter 160 performs reduction of nitrogen oxides (NOx), wherein NOx species are chemically reduced into nitrogen (N2) and oxygen (O2) under near-stoichiometric or slightly rich exhaust conditions. The catalytic converter 160 further performs oxidation of carbon monoxide (CO), wherein carbon monoxide is oxidized into carbon dioxide (CO2). The catalytic converter 160 further performs oxidation of unburned hydrocarbons (HC), wherein unburned or partially combusted hydrocarbons are oxidized into carbon dioxide (CO2) and water (H2O). The conversion efficiency of the catalytic converter 160 is highly sensitive to the air–fuel ratio of the combustion exhaust gases 178 and achieves maximum simultaneous conversion of nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC) only when the air–fuel ratio is maintained within a narrow window around stoichiometric conditions. Even small deviations toward rich or lean operation can result in a significant reduction in conversion efficiency for one or more of the three regulated exhaust gas constituents.
The post-catalyst lambda sensor 162 is positioned downstream of the catalytic converter 160 in the exhaust system 176. In one or more embodiments, the post-catalyst lambda sensor 162 is implemented as a narrowband-type lambda sensor configured to measure the air–fuel ratio over a relatively narrow operating range, for example approximately from lambda 0.95 to lambda 1.05. The post-catalyst lambda sensor 162 is primarily configured to monitor the operational health and conversion efficiency of the catalytic converter 160. The signal from the post-catalyst lambda sensor 162 is communicated to the engine control unit 146.
Overall operation of the internal combustion engine system 100 is governed by the engine control unit 146, which is sometimes also referred to as an engine management system (EMS), an engine control module (ECM), an engine controller, or a controller, without any limitations. The engine control unit 146 is electrically and communicatively coupled to a plurality of sensors and actuators via one or more electrical wiring harnesses, signal lines, and power supply lines. The sensors communicatively coupled to the engine control unit 146 include, but are not limited to, the crankshaft position sensor 152, the camshaft position sensor 164, the boost pressure and temperature sensor 134, the manifold air pressure and temperature sensor 154, the fuel rail pressure and temperature sensor 166, the exhaust gas sensor 158, the post-catalyst lambda sensor 162, the accelerator pedal 156, and other temperature, pressure, position, and diagnostic sensors associated with the internal combustion engine system 100. The actuators communicatively coupled to the engine control unit 146 include, but are not limited to, the at least one gaseous fuel injector 128, the ignition coil 148, the electronic throttle body 130, fuel pressure regulating elements associated with the high-pressure fuel regulator 170, turbocharger-related control elements, and valve train actuation mechanisms, where applicable. The wiring harness provides structured routing of electrical power, grounding, and bidirectional signal communication between the engine control unit 146 and the respective sensors and actuators, thereby enabling real-time monitoring, closed-loop control, diagnostics, fault detection, and safety functions. In one or more embodiments, the wiring harness may further support standardized communication protocols, electromagnetic shielding, redundancy, and fail-safe configurations to ensure reliable operation under varying environmental and operating conditions.
The engine control unit 146 is configured to acquire a plurality of engine operating parameters including at least engine speed and engine load. The engine speed is determined by the engine control unit 146 based on the signal received from the crankshaft position sensor 152. The engine load is determined by the engine control unit 146 based on one or more of the signal received from the manifold air pressure and temperature sensor 154, the signal received from the boost pressure and temperature sensor 134, the position of the electronic throttle body 130, and the operator input from the accelerator pedal 156. Additional engine operating parameters acquired by the engine control unit 146 include, but are not limited to, coolant temperature, intake air temperature, fuel rail pressure, fuel rail temperature, ambient pressure, and ambient temperature. Based on the acquired engine operating parameters, the engine control unit 146 generates a base fuel injection command from a feed-forward fuel map, commands the at least one gaseous fuel injector 128, and commands the ignition system 174, as described in further detail with reference to FIGS. 2 through 5.
Referring to FIG. 2, illustrated is a block diagram representation of the engine control unit 146 and associated components for adaptive fuel injection and ignition control in the internal combustion engine, in accordance with one or more embodiments of the present invention. As described with reference to FIG. 1, the engine control unit 146 governs overall operation of the internal combustion engine system 100, including fuel injection control, ignition timing control, air management, and diagnostics. FIG. 2 illustrates the internal architecture of the engine control unit 146 and the communicative coupling of the engine control unit 146 to the plurality of sensors and actuators of the internal combustion engine system 100 that are relevant to the adaptive fuel injection and ignition control disclosed herein.
The engine control unit 146 comprises one or more processing units 200 and a memory unit 202 communicatively coupled to the one or more processing units 200. The one or more processing units 200 and the memory unit 202 are interconnected via a communication bus 212 for passing information among the components of the engine control unit 146. It may be appreciated that the engine control unit 146 described herein may be implemented in various forms of hardware, firmware, software, or a combination thereof. In an example, the engine control unit 146 may be embodied as a dedicated automotive electronic control unit, a microcontroller-based system, or a programmable logic device configured for real-time engine control functions.
Generally, as used herein, the term “processing unit” refers to a computational element that is operable to respond to and process instructions that drive the engine control unit 146. The one or more processing units 200 include, but are not limited to, a microprocessor, a microcontroller, a complex instruction set computing (CISC) microprocessor, a reduced instruction set (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or any other type of processing circuit suitable for real-time engine control applications. Furthermore, the term “processing unit” may refer to one or more individual processors, processing devices, and various elements associated with a processing device that may be shared by other processing devices. The one or more processing units 200 are configured to execute machine-readable instructions stored in the memory unit 202 to perform the steps of the method for adaptive fuel injection and ignition control as described herein. In one or more embodiments, the one or more processing units 200 may include one or more processing cores, with each processing core configured to perform independently. In one or more embodiments, the one or more processing units 200 may be accompanied by one or more specialized components to perform certain processing functions and tasks, such as one or more digital signal processors (DSP), one or more application-specific integrated circuits (ASIC), or one or more field programmable gate arrays (FPGA), to accelerate computation of fuel injection commands, ignition timing commands, and adaptive fuel correction values.
The memory unit 202 is communicatively coupled to the one or more processing units 200 via the communication bus 212. The memory unit 202 may comprise volatile memory and non-volatile memory. The one or more processing units 200 may execute instructions and process data stored in the memory unit 202. The memory unit 202 may include any suitable elements for storing data and machine-readable instructions, such as read only memory (ROM), random access memory (RAM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory, and the like. The memory unit 202 stores machine-readable instructions that, when executed by the one or more processing units 200, cause the engine control unit 146 to perform the steps of the method for adaptive fuel injection and ignition control as described herein. In particular, the memory unit 202 stores an adaptive fuel injection and ignition control module 214 in the form of machine-readable instructions executable by the one or more processing units 200. The adaptive fuel injection and ignition control module 214 is configured to perform the method steps for adaptive fuel injection and ignition control in the internal combustion engine configured for operation on gaseous fuel, as described in detail with reference to FIGS. 3 and 4.
The memory unit 202 further stores a feed-forward fuel map 208. The feed-forward fuel map 208 is a pre-calibrated look-up table that provides a base fuel injection quantity as a function of the engine operating parameters, including at least the engine speed and the engine load, and the feed-forward fuel map 208 is calibrated assuming a nominal or reference fuel composition. The engine control unit 146 generates the base fuel injection command by looking up the appropriate base fuel injection quantity from the feed-forward fuel map 208 based on the currently acquired engine speed and engine load. The memory unit 202 further stores a feed-forward ignition timing map 210. The feed-forward ignition timing map 210 is a pre-calibrated look-up table that provides a base ignition timing as a function of the engine operating parameters, including at least the engine speed and the engine load. The base ignition timing represents the ignition timing at which the spark plug 118 produces the spark discharge under nominal operating conditions and nominal fuel composition.
The memory unit 202 further stores a two-dimensional adaptive fuel learning map 206. The two-dimensional adaptive fuel learning map 206 is indexed by the engine speed and the engine load, and the two-dimensional adaptive fuel learning map 206 stores adaptive fuel correction values independently for each region of the engine operating range. Each region of the two-dimensional adaptive fuel learning map 206 corresponds to a distinct combination of engine speed and engine load, and the adaptive fuel correction value stored for each region represents the learned correction applicable to that particular combination of engine speed and engine load. The two-dimensional adaptive fuel learning map 206 enables operating-region-specific correction rather than a single uniform correction value applied across the entire operating range of the internal combustion engine. The two-dimensional adaptive fuel learning map 206 is described in further detail with reference to FIGS. 3 and 4.
The memory unit 202 further comprises a non-volatile memory 204. The non-volatile memory 204 is a portion of the memory unit 202 that retains stored data across power-off and power-on cycles of the engine control unit 146, such that data stored in the non-volatile memory 204 is preserved when electrical power is removed from the engine control unit 146, for example during an engine stop cycle, and is available when electrical power is restored to the engine control unit 146, for example during a subsequent engine start cycle. In one or more embodiments, the non-volatile memory 204 is implemented as EEPROM, flash memory, or other non-volatile storage element. The engine control unit 146 is configured to store the adaptive fuel correction values of the two-dimensional adaptive fuel learning map 206 in the non-volatile memory 204. The engine control unit 146 is configured to retain the stored adaptive fuel correction values in the non-volatile memory 204 across successive engine start and engine stop cycles of the internal combustion engine. Upon a subsequent engine start, the engine control unit 146 is configured to retrieve the stored adaptive fuel correction values from the non-volatile memory 204 and apply the stored adaptive fuel correction values to the fuel injection commands, thereby enabling immediate stabilization of the air–fuel ratio without requiring a new learning cycle. This arrangement is particularly advantageous when the internal combustion engine is operated on a gaseous fuel that was previously learned during a prior engine operating cycle, as the stored adaptive fuel correction values from the prior engine operating cycle are immediately available upon the subsequent engine start.
The engine control unit 146 is communicatively coupled to the plurality of sensors and actuators of the internal combustion engine system 100 as described with reference to FIG. 1. With reference to the sensor inputs, the engine control unit 146 receives the signal from the crankshaft position sensor 152 indicative of the engine speed and the top dead center position. The engine control unit 146 receives the signal from the camshaft position sensor 164 indicative of the camshaft angular position. The engine control unit 146 receives the signal from the manifold air pressure and temperature (P/T) sensor 154 indicative of the pressure and the temperature of the intake charge within the intake manifold 126. The engine control unit 146 receives the signal from the boost pressure and temperature sensor 134 indicative of the pressure and the temperature of the boosted intake air upstream of the electronic throttle body 130. The engine control unit 146 receives the signal from the fuel rail pressure and temperature sensor 166 indicative of the pressure and the temperature of the gaseous fuel within the fuel rail 150. The engine control unit 146 receives the air–fuel ratio signal from the exhaust gas sensor 158 indicative of the air–fuel ratio of the combusted gases upstream of the catalytic converter 160. The engine control unit 146 receives the signal from the post-catalyst lambda sensor 162 indicative of the air–fuel ratio of the combusted gases downstream of the catalytic converter 160. The engine control unit 146 further receives the operator input from the accelerator pedal 156 indicative of a desired engine torque or engine load.
With reference to the actuator outputs, the engine control unit 146 outputs the fuel injection command to the at least one gaseous fuel injector 128 to control the timing and duration of each fuel injection event. The fuel injection command defines the injector opening duration or fuel injection pulse width, which determines the quantity of gaseous fuel injected per combustion cycle. The engine control unit 146 outputs the ignition command to the ignition system 174, and more particularly to the ignition coil 148, to control the ignition timing at which the spark plug 118 produces the spark discharge. The engine control unit 146 further outputs a throttle position command to the electronic throttle body 130 to regulate the quantity of intake air admitted to the intake manifold 126. The engine control unit 146 may further output commands to fuel pressure regulating elements associated with the high-pressure fuel regulator 170 and to turbocharger-related control elements, where applicable.
Referring to FIGS. 1 and 2 in combination, various steps of the method for adaptive fuel injection and ignition control, as described hereinafter with reference to FIGS. 3 and 4, are executed by the engine control unit 146, and specifically by the one or more processing units 200 of the engine control unit 146 executing the adaptive fuel injection and ignition control module 214 stored in the memory unit 202. It may be appreciated that although the method is illustrated and described as a sequence of steps, it may be contemplated that various embodiments of the method may be performed in any order or different combinations, and need not include all of the illustrated steps.
Referring to FIG. 5, illustrated is a representative graph depicting the catalytic conversion efficiency of the catalytic converter 160, implemented as a three-way catalytic converter, as a function of a pre-catalyst air–fuel ratio expressed in terms of lambda (λ), in accordance with one or more embodiments of the present invention. In FIG. 5, the horizontal axis represents the pre-catalyst lambda value, which is the air–fuel ratio measured by the exhaust gas sensor 158 upstream of the catalytic converter 160, expressed as a ratio of the actual air–fuel ratio to the stoichiometric air–fuel ratio. The vertical axis represents the catalytic conversion efficiency expressed as a percentage. Separate curves are shown for nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC).
The graph, as shown in FIG. 5, demonstrates that the catalytic converter 160, implemented as a three-way catalytic converter, achieves optimum and simultaneously high conversion efficiency for all three regulated exhaust gas constituents, nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC), when the air–fuel ratio is maintained at or near the stoichiometric condition, corresponding to a lambda value of approximately 1.0. In this narrow stoichiometric region, the conversion efficiency of the catalytic converter 160 for all three regulated exhaust gas constituents typically remains at very high levels, for example in the range of approximately 95% to 99%.
The graph further illustrates that when the air–fuel ratio deviates from the stoichiometric condition toward a rich mixture, corresponding to a lambda value less than 1.0, the simultaneous conversion of all three regulated exhaust gas constituents is no longer at an optimum level. Under rich operating conditions, the conversion efficiency of the catalytic converter 160 for carbon monoxide (CO) and unburned hydrocarbons (HC) decreases significantly due to insufficient oxygen availability in the combustion exhaust gases 178, resulting in elevated emissions of carbon monoxide (CO) and unburned hydrocarbons (HC), despite relatively high conversion efficiency for nitrogen oxides (NOx). Conversely, when the air–fuel ratio deviates from the stoichiometric condition toward a lean mixture, corresponding to a lambda value greater than 1.0, excess oxygen in the combustion exhaust gases 178 inhibits the reduction reactions of nitrogen oxides (NOx), causing a sharp decline in the conversion efficiency of the catalytic converter 160 for nitrogen oxides (NOx), while the conversion efficiency for carbon monoxide (CO) and unburned hydrocarbons (HC) remains comparatively high.
Accordingly, the graph highlights that operation of the internal combustion engine away from the stoichiometric lambda window results in increased tailpipe emissions of either nitrogen oxides (NOx) under lean conditions or carbon monoxide (CO) and unburned hydrocarbons (HC) under rich conditions. This illustrates the importance of maintaining the air–fuel ratio within a narrow stoichiometric range for effective three-way catalytic conversion. The target air–fuel ratio, as used in the present invention, is the stoichiometric air–fuel ratio corresponding to a lambda value of approximately 1.0, and the system, the method, and the engine control unit of the present invention maintain the air–fuel ratio within the narrow stoichiometric window illustrated in FIG. 5 through the adaptive fuel injection and ignition control described herein. By deriving the adaptive fuel correction value and applying the adaptive fuel correction value to adjust subsequent fuel injection commands, the engine control unit 146 minimizes the deviation between the received air–fuel ratio signal and the target air–fuel ratio, thereby maintaining the air–fuel ratio within the narrow stoichiometric window. This results in sustained high conversion efficiency of the catalytic converter 160 for all three regulated exhaust gas constituents, reduced total tailpipe emissions, prevention of emission excursions under real-world driving conditions, and preservation of the effectiveness of the catalytic converter 160 over the useful life of the internal combustion engine.
Referring to FIG. 3, illustrated is a flowchart of a method 300 for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, in accordance with one or more embodiments of the present invention. The method 300 is executed by the engine control unit 146, and specifically by the one or more processing units 200 of the engine control unit 146 executing the adaptive fuel injection and ignition control module 214 stored in the memory unit 202, as described with reference to FIG. 2. The method 300 illustrates the principal steps of the adaptive fuel injection and ignition control in a simplified form, and a more detailed implementation of the method 300 is described with reference to FIG. 4.
At step 302, the method 300 comprises commanding the at least one gaseous fuel injector 128 to inject a quantity of gaseous fuel into the combustion chamber 106 of the internal combustion engine. The engine control unit 146 outputs a fuel injection command to the at least one gaseous fuel injector 128, the fuel injection command defining the injector opening duration or fuel injection pulse width that determines the quantity of gaseous fuel injected into the combustion chamber 106. The gaseous fuel is mixed with intake air and combusted within the combustion chamber 106.
At step 304, the method 300 comprises receiving an air–fuel ratio signal from the exhaust gas sensor 158 positioned upstream of the catalytic converter 160 in the exhaust system 176 of the internal combustion engine. The air–fuel ratio signal is indicative of the air–fuel ratio of the combusted gases flowing through the exhaust system 176. The engine control unit 146 receives the air–fuel ratio signal from the exhaust gas sensor 158, and in one or more embodiments, the exhaust gas sensor 158 is a wideband-type lambda sensor configured to measure the air–fuel ratio of the combusted gases over a range extending from lean conditions to rich conditions.
At step 306, the method 300 comprises deriving an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio. The engine control unit 146 computes the deviation between the received air–fuel ratio signal and the target air–fuel ratio, wherein the target air–fuel ratio is, in one or more embodiments, the stoichiometric air–fuel ratio. Based on the computed deviation, the engine control unit 146 derives the adaptive fuel correction value. The adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics, without use of a direct fuel composition sensor.
At step 308, the method 300 comprises applying the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio. The engine control unit 146 applies the adaptive fuel correction value to modify the base fuel injection command generated from the feed-forward fuel map 208, such that the adjusted fuel injection command accounts for the actual fuel composition, fuel calorific value, and fuel injector flow characteristics. By applying the adaptive fuel correction value, the engine control unit 146 reduces the deviation between the received air–fuel ratio signal and the target air–fuel ratio, thereby maintaining the air–fuel ratio within the narrow stoichiometric window required for high conversion efficiency of the catalytic converter 160.
At step 310, the method 300 comprises determining whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold. The engine control unit 146 evaluates the magnitude of the adaptive fuel correction value against the predefined threshold. The predefined threshold is a predetermined value, exceedance of which is indicative of inferior fuel quality, abnormal combustion characteristics, or conditions requiring ignition timing correction. If the magnitude of the adaptive fuel correction value does not exceed the predefined threshold, the engine control unit 146 maintains the base ignition timing from the feed-forward ignition timing map 210 and the method 300 continues with normal engine operation.
At step 312, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the method 300 comprises commanding the ignition system 174 to retard an ignition timing relative to a base ignition timing. The engine control unit 146 outputs an ignition command to the ignition system 174 to retard the ignition timing, thereby delaying the point in time during the engine cycle at which the spark plug 118 produces the spark discharge. The retarding of the ignition timing reduces peak combustion pressure, suppresses knock and abnormal combustion, lowers thermal stress on engine components, and shifts engine operation into a safe and stable combustion zone. The engine control unit 146 commands the ignition system 174 to retard the ignition timing without reliance on a knock sensor, and the ignition timing retard is based on the magnitude of the adaptive fuel correction value exceeding the predefined threshold.
The method 300 is continuously and cyclically executed during operation of the internal combustion engine, such that the engine control unit 146 continuously commands fuel injection, receives the air–fuel ratio signal, derives and applies the adaptive fuel correction value, and determines whether the ignition timing requires retarding based on the magnitude of the adaptive fuel correction value. The continuous and cyclic execution of the method 300 enables the engine control unit 146 to dynamically adapt the fuel injection commands and the ignition timing in response to changes in fuel composition, fuel calorific value, fuel injector flow characteristics, and other fuel delivery uncertainties throughout the operation of the internal combustion engine.
Referring to FIG. 4, illustrated is a detailed flowchart of a method 400 for adaptive fuel injection and ignition control depicting data acquisition, computation, fuel learning, and ignition timing correction steps, in accordance with one or more embodiments of the present invention. The method 400 provides a detailed implementation of the method 300 described with reference to FIG. 3. The method 400 is executed by the engine control unit 146, and specifically by the one or more processing units 200 of the engine control unit 146 executing the adaptive fuel injection and ignition control module 214 stored in the memory unit 202. The method 400 is continuously and cyclically executed during operation of the internal combustion engine, such that the steps of the method 400 are repeated in each engine control cycle throughout the operation of the internal combustion engine. The method 400 enables the engine control unit 146 to perform real-time identification, compensation, correction, learning, and adaptation of the fuel injection quantity delivered to the combustion chamber 106 in response to fuel composition variability, fuel quality deviation, and fuel injector flow drift, and to autonomously adjust the ignition timing when the magnitude of the adaptive fuel correction value exceeds the predefined threshold.
At step 402, the method 400 begins with initiation of engine operation. The engine control unit 146 is activated upon engine start, and the one or more processing units 200 of the engine control unit 146 begin executing the adaptive fuel injection and ignition control module 214 stored in the memory unit 202. Upon initiation of engine operation, the engine control unit 146 enters a continuous cyclic control mode in which the steps of the method 400 are executed repeatedly throughout the duration of engine operation. Upon engine start, the engine control unit 146 retrieves the stored adaptive fuel correction values from the non-volatile memory 204, if available from a prior engine operating cycle, and applies the stored adaptive fuel correction values to the fuel injection commands, as described in further detail at step 422. The retrieval and application of the stored adaptive fuel correction values upon engine start enables immediate stabilization of the air–fuel ratio, reduces transient deviation between the received air–fuel ratio signal and the target air–fuel ratio, and avoids prolonged off-stoichiometric operation that would otherwise occur if a new learning cycle were required from a baseline state.
In the context of the initiation of engine operation at step 402, the engine control unit 146 initializes the internal variables, counters, and state machines associated with the adaptive fuel injection and ignition control module 214. The engine control unit 146 reads the current state of all communicatively coupled sensors, including the crankshaft position sensor 152, the camshaft position sensor 164, the manifold air pressure and temperature sensor 154, the boost pressure and temperature sensor 134, the fuel rail pressure and temperature sensor 166, the exhaust gas sensor 158, and the accelerator pedal 156. The engine control unit 146 verifies the validity and plausibility of the sensor signals to confirm that the sensors are operating within expected ranges. If the engine control unit 146 has stored adaptive fuel correction values in the non-volatile memory 204 from a prior engine operating cycle, the engine control unit 146 loads the stored adaptive fuel correction values from the two-dimensional adaptive fuel learning map 206 stored in the non-volatile memory 204, and the stored adaptive fuel correction values are applied to the fuel injection commands from the first combustion cycle following the engine start. This immediate application of the stored adaptive fuel correction values upon engine start is particularly advantageous when the internal combustion engine is operated on a gaseous fuel that was previously learned during a prior engine operating cycle, such as when the vehicle has been refueled with the same gaseous fuel type or when the gaseous fuel remaining in the high-pressure storage cylinder 172 has not been changed between successive engine operating cycles.
At step 404, the engine control unit 146 performs data acquisition, wherein the engine control unit 146 acquires a plurality of engine operating parameters including at least engine speed and engine load. The engine speed is determined by the engine control unit 146 based on the signal received from the crankshaft position sensor 152, which detects the rotational speed of the crankshaft 110. The engine load is determined by the engine control unit 146 based on one or more of the signal received from the manifold air pressure and temperature sensor 154 indicative of the pressure and temperature of the intake charge within the intake manifold 126, the signal received from the boost pressure and temperature sensor 134 indicative of the pressure and temperature of the boosted intake air, the position of the electronic throttle body 130, and the operator input from the accelerator pedal 156. Additional engine operating parameters acquired by the engine control unit 146 at step 404 include, but are not limited to, coolant temperature, intake air temperature, ambient pressure, ambient temperature, fuel rail pressure from the fuel rail pressure and temperature sensor 166, fuel rail temperature from the fuel rail pressure and temperature sensor 166, and camshaft position from the camshaft position sensor 164.
The data acquisition at step 404 provides the engine control unit 146 with the information required to determine the current operating state of the internal combustion engine and to generate the appropriate fuel injection commands and ignition timing commands. The engine speed and the engine load are the primary indices used by the engine control unit 146 to access the feed-forward fuel map 208, the feed-forward ignition timing map 210, and the two-dimensional adaptive fuel learning map 206. The accuracy and timeliness of the data acquisition at step 404 are important for the performance of the adaptive fuel injection and ignition control, as the acquired engine operating parameters directly influence the base fuel injection command, the base ignition timing, and the region of the two-dimensional adaptive fuel learning map 206 in which the adaptive fuel correction value is stored and retrieved. The engine control unit 146 performs the data acquisition at step 404 at a rate commensurate with the engine control cycle, such that the engine operating parameters are updated for each combustion cycle or at a predetermined sampling interval.
At step 406, the engine control unit 146 performs a determination step to calculate or estimate engine parameters based on the acquired engine operating parameters from step 404. The engine parameters calculated or estimated at step 406 include, but are not limited to, air consumption of the internal combustion engine, fuel consumption of the internal combustion engine, and the base ignition timing required for the current operating condition. The air consumption is determined by the engine control unit 146 based on the signals from the manifold air pressure and temperature sensor 154, the boost pressure and temperature sensor 134, and the engine speed, using a speed-density method or a mass airflow calculation method or any other suitable method known in the art. The fuel consumption is determined as a function of the air consumption and the target air–fuel ratio, which in one or more embodiments is the stoichiometric air–fuel ratio. The base ignition timing is determined by the engine control unit 146 by accessing the feed-forward ignition timing map 210 stored in the memory unit 202, based on the currently acquired engine speed and engine load.
The determination at step 406 provides the engine control unit 146 with the baseline engine parameters upon which the base fuel injection command is calculated and upon which the ignition timing is initially set. The base ignition timing determined at step 406 represents the ignition timing applicable under nominal conditions and nominal fuel composition, and the base ignition timing may be subsequently modified by the engine control unit 146 based on the magnitude of the adaptive fuel correction value as described at steps 424 through 428. The air consumption and fuel consumption determined at step 406 are used by the engine control unit 146 in conjunction with the feed-forward fuel map 208 to generate the base fuel injection command at step 408.
At step 408, the engine control unit 146 generates a base fuel injection command based on the feed-forward fuel map 208 and the acquired engine operating parameters. The engine control unit 146 accesses the feed-forward fuel map 208 stored in the memory unit 202 using the currently acquired engine speed and engine load as input indices. The feed-forward fuel map 208 returns a base fuel injection quantity corresponding to the current combination of engine speed and engine load, assuming a nominal or reference fuel composition. Based on the base fuel injection quantity returned from the feed-forward fuel map 208, the engine control unit 146 calculates the injector opening duration, also referred to as the fuel injection pulse width, which defines the time duration for which the at least one gaseous fuel injector 128 is commanded to remain open during each fuel injection event. The injector opening duration is calculated by the engine control unit 146 taking into account the fuel rail pressure from the fuel rail pressure and temperature sensor 166, the fuel rail temperature from the fuel rail pressure and temperature sensor 166, and the known flow characteristics of the at least one gaseous fuel injector 128 under the assumed nominal fuel composition.
In addition to the base fuel injection quantity derived from the feed-forward fuel map 208, the engine control unit 146 applies the adaptive fuel correction value, if available, to modify the base fuel injection command. When the adaptive fuel correction value has been previously derived and stored in the two-dimensional adaptive fuel learning map 206, the engine control unit 146 retrieves the adaptive fuel correction value corresponding to the current engine speed and engine load from the two-dimensional adaptive fuel learning map 206 and applies the adaptive fuel correction value to the base fuel injection quantity. The application of the adaptive fuel correction value adjusts the injector opening duration to account for the actual fuel composition, fuel calorific value, and fuel injector flow characteristics, which may differ from the nominal or reference values assumed in the feed-forward fuel map 208. This combination of feed-forward fuel map compensation and adaptive fuel correction value compensation enables the engine control unit 146 to generate an adjusted fuel injection command that more accurately reflects the actual fuel delivery requirements of the internal combustion engine. The generation of the base fuel injection command at step 408 corresponds to the step of generating a base fuel injection command based on a feed-forward fuel map and at least engine speed and engine load of the internal combustion engine.
At step 410, the engine control unit 146 commands the at least one gaseous fuel injector 128 to inject a quantity of gaseous fuel into the combustion chamber 106 of the internal combustion engine based on the base fuel injection command, as adjusted by the adaptive fuel correction value where applicable. The engine control unit 146 outputs the fuel injection command to the at least one gaseous fuel injector 128, the fuel injection command comprising the calculated injector opening duration or fuel injection pulse width. Upon receiving the fuel injection command, the at least one gaseous fuel injector 128 opens for the commanded duration, allowing a metered quantity of gaseous fuel to flow from the fuel rail 150 through the at least one gaseous fuel injector 128 into the intake port 124, or in alternative embodiments directly into the combustion chamber 106. The gaseous fuel mixes with the intake air to form the air–gaseous fuel mixture, which is then drawn into the combustion chamber 106 through the intake valve 114 during the intake stroke of the piston 104.
Following injection at step 410, the air–gaseous fuel mixture is compressed by the piston 104 during the compression stroke, and the ignition system 174 initiates combustion of the compressed air–gaseous fuel mixture at the commanded ignition timing. The combustion of the compressed air–gaseous fuel mixture produces combustion forces that drive the piston 104 downward during the power stroke, and the combustion forces are transmitted to the crankshaft 110 via the connecting rod 112. The combustion exhaust gases 178 are subsequently expelled from the combustion chamber 106 through the exhaust valve 116 during the exhaust stroke and flow into the exhaust system 176. The commanding of the at least one gaseous fuel injector 128 at step 410 corresponds to the step of commanding at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine.
At step 412, the engine control unit 146 performs further data acquisition by receiving the air–fuel ratio signal from the exhaust gas sensor 158 positioned upstream of the catalytic converter 160 in the exhaust system 176 of the internal combustion engine. The air–fuel ratio signal received from the exhaust gas sensor 158 is indicative of the air–fuel ratio of the combusted gases flowing through the exhaust system 176 upstream of the catalytic converter 160. The engine control unit 146 reads the air–fuel ratio signal from the exhaust gas sensor 158 after combustion has occurred and after the combustion exhaust gases 178 have reached the location of the exhaust gas sensor 158 in the exhaust system 176. In one or more embodiments, the exhaust gas sensor 158 is implemented as a wideband-type lambda sensor, and the air–fuel ratio signal represents the lambda value of the combusted gases over a range extending from lean conditions to rich conditions, for example from approximately lambda 0.65 to lambda 10.
The receiving of the air–fuel ratio signal at step 412 provides the engine control unit 146 with a measurement of the actual air–fuel ratio at which the combustion occurred within the combustion chamber 106. The measured air–fuel ratio inherently reflects the combined effects of the actual fuel composition, the actual fuel calorific value, the actual fuel injector flow characteristics, the actual fuel rail pressure, and any other factors that influence the quantity of gaseous fuel actually delivered to the combustion chamber 106 relative to the quantity of intake air. Because the exhaust gas sensor 158 measures the oxygen content present in the combustion exhaust gases 178, the air–fuel ratio signal provides an indirect but accurate indication of the actual stoichiometry of the air–gaseous fuel mixture that was combusted.
At step 414, the engine control unit 146 performs a computation step, wherein the engine control unit 146 computes a deviation between the received air–fuel ratio signal and the target air–fuel ratio. The target air–fuel ratio is, in one or more embodiments, the stoichiometric air–fuel ratio corresponding to a lambda value of approximately 1.0. The engine control unit 146 determines the difference between the lambda value indicated by the received air–fuel ratio signal from the exhaust gas sensor 158 and the lambda value corresponding to the target air–fuel ratio. A positive deviation indicates that the actual air–fuel ratio is leaner than the target air–fuel ratio, meaning that less gaseous fuel was delivered to the combustion chamber 106 than required for stoichiometric combustion. A negative deviation indicates that the actual air–fuel ratio is richer than the target air–fuel ratio, meaning that more gaseous fuel was delivered to the combustion chamber 106 than required for stoichiometric combustion.
The computed deviation at step 414 quantifies the error between the intended air–fuel ratio and the actual air–fuel ratio, and the magnitude and direction of the computed deviation provide the engine control unit 146 with information about whether the fuel injection command needs to be increased or decreased to bring the air–fuel ratio closer to the target air–fuel ratio. The computed deviation may arise from one or more of fuel composition variability, wherein the actual fuel calorific value or stoichiometric air–fuel ratio differs from the nominal values assumed in the feed-forward fuel map 208, fuel injector flow drift, wherein the actual flow characteristics of the at least one gaseous fuel injector 128 have changed due to aging, contamination, deposits, or wear, pressure regulation deviation, wherein the actual fuel rail pressure differs from the expected fuel rail pressure, and other environmental or operating factors. The computation of the deviation at step 414 corresponds to the step of computing a deviation between the received air–fuel ratio signal and a target air–fuel ratio.
At step 416, the engine control unit 146 applies a closed-loop fuel correction by adjusting the fuel injection quantity to reduce the air–fuel ratio deviation computed at step 414. The closed-loop fuel correction at step 416 is a short-term correction that adjusts the fuel injection command in the current or subsequent engine control cycle based on the deviation computed at step 414. The engine control unit 146 increases the fuel injection quantity if the computed deviation indicates a lean condition, and the engine control unit 146 decreases the fuel injection quantity if the computed deviation indicates a rich condition. The closed-loop fuel correction at step 416 provides an immediate, cycle-by-cycle adjustment to reduce the air–fuel ratio deviation and bring the air–fuel ratio closer to the target air–fuel ratio.
The closed-loop fuel correction at step 416 operates in conjunction with, but is distinct from, the adaptive fuel correction value derived at step 420 (discussed later) and stored in the two-dimensional adaptive fuel learning map 206. The closed-loop fuel correction at step 416 is a short-term, reactive correction that responds to the air–fuel ratio deviation in each engine control cycle, whereas the adaptive fuel correction value derived at step 420 is a longer-term, learned correction that captures persistent deviations arising from fuel composition variability, fuel injector flow drift, and other systematic fuel delivery errors. The closed-loop fuel correction at step 416 reduces the immediate air–fuel ratio deviation, and over time, the persistent component of the closed-loop fuel correction is absorbed into the adaptive fuel correction value through the learning process described at steps 418 through 422. The application of the closed-loop fuel correction at step 416 corresponds to the step of applying the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio, in combination with the adaptive fuel correction value applied at steps 420 and 430.
At step 418, a decision step is executed by the engine control unit 146 to determine whether predefined fuel learning conditions are satisfied. The predefined fuel learning conditions are a set of conditions that must be met before the engine control unit 146 proceeds to derive or update the adaptive fuel correction value. The predefined fuel learning conditions are established to ensure that the adaptive fuel correction value is derived under stable and representative engine operating conditions, such that the derived adaptive fuel correction value accurately reflects the persistent fuel delivery deviation and is not influenced by transient or anomalous engine behaviour. The predefined fuel learning conditions include at least one of steady-state operation of the internal combustion engine, absence of knock in the internal combustion engine, validity of sensor signals associated with the internal combustion engine, and operation of the internal combustion engine within predefined temperature ranges.
In the context of the predefined fuel learning conditions at step 418, steady-state operation of the internal combustion engine refers to a condition in which the engine speed, the engine load, and the air–fuel ratio are relatively stable and are not undergoing rapid transient changes. The engine control unit 146 evaluates the rates of change of the engine speed, the engine load, and other relevant engine operating parameters to determine whether the internal combustion engine is operating in a steady-state condition. Absence of knock in the internal combustion engine refers to a condition in which abnormal combustion events, such as knock or detonation, are not detected or inferred by the engine control unit 146. Validity of sensor signals associated with the internal combustion engine refers to a condition in which the signals from the exhaust gas sensor 158, the crankshaft position sensor 152, the manifold air pressure and temperature sensor 154, the fuel rail pressure and temperature sensor 166, and other sensors communicatively coupled to the engine control unit 146 are within expected ranges and are not indicating a fault or malfunction. Operation of the internal combustion engine within predefined temperature ranges refers to a condition in which the coolant temperature, the intake air temperature, and other temperature parameters of the internal combustion engine are within ranges that are suitable for fuel learning, for example after the internal combustion engine has reached a warmed-up operating condition.
If the predefined fuel learning conditions are not satisfied at step 418, the method 400 returns to step 408, and the engine control unit 146 continues to generate the base fuel injection command from the feed-forward fuel map 208 and apply the closed-loop fuel correction from step 416, without updating the adaptive fuel correction value or the two-dimensional adaptive fuel learning map 206. If the predefined fuel learning conditions are satisfied at step 418, the method 400 proceeds to step 420. The decision at step 418 ensures that the adaptive fuel correction value is derived and updated only under conditions in which the derived adaptive fuel correction value is likely to be accurate and representative, and prevents the two-dimensional adaptive fuel learning map 206 from being updated with values derived during transient or fault conditions that may not be representative of the actual fuel delivery deviation.
At step 420, the engine control unit 146 performs a determination step to derive the adaptive fuel correction value based on the computed deviation from step 414. The engine control unit 146 derives the adaptive fuel correction value that represents the persistent component of the air–fuel ratio deviation that is attributable to fuel composition variability, fuel calorific value deviation, fuel injector flow drift, pressure regulation deviation, or other systematic fuel delivery errors. The adaptive fuel correction value is distinguished from the short-term closed-loop fuel correction applied at step 416 in that the adaptive fuel correction value represents the longer-term learned correction that captures persistent deviations rather than cycle-by-cycle fluctuations. The engine control unit 146 derives the adaptive fuel correction value by analyzing the closed-loop fuel correction values computed over multiple engine control cycles during steady-state operation and extracting the persistent offset component therefrom.
In one or more embodiments, the engine control unit 146 derives the adaptive fuel correction value based on the computed deviation in combination with historical injector opening duration data associated with the at least one gaseous fuel injector 128. The historical injector opening duration data represents past injector opening durations or fuel injection pulse widths recorded by the engine control unit 146 during prior operation of the internal combustion engine. By combining the computed deviation with the historical injector opening duration data, the engine control unit 146 accounts for the relationship between the commanded fuel injection quantity and the actual fuel delivery, and the engine control unit 146 derives the adaptive fuel correction value that more accurately captures the fuel delivery deviation. The use of the historical injector opening duration data in combination with the computed deviation enables the engine control unit 146 to distinguish between fuel delivery deviations arising from fuel composition variability and fuel delivery deviations arising from fuel injector flow drift, and to derive an adaptive fuel correction value that compensates for both sources of deviation. The derivation of the adaptive fuel correction value at step 420 corresponds to the step of deriving an adaptive fuel correction value based on the computed deviation, and more particularly to the step of deriving the adaptive fuel correction value based on the computed deviation in combination with historical injector opening duration data associated with the at least one gaseous fuel injector.
At step 420, the engine control unit 146 also identifies the corresponding region within the two-dimensional adaptive fuel learning map 206 based on the currently acquired engine speed and engine load. The two-dimensional adaptive fuel learning map 206 is organized as a grid of regions, also referred to as speed–load cells, wherein each region corresponds to a distinct combination of engine speed and engine load. The engine control unit 146 determines which region of the two-dimensional adaptive fuel learning map 206 corresponds to the current engine speed and engine load, and the adaptive fuel correction value derived at step 420 is associated with the identified region. The identification of the corresponding region ensures that the adaptive fuel correction value is stored and applied in an operating-region-specific manner, such that the adaptive fuel correction value for one combination of engine speed and engine load is independent of the adaptive fuel correction value for a different combination of engine speed and engine load.
The operating-region-specific storage of the adaptive fuel correction value recognizes that fuel delivery deviations arising from fuel composition variability, fuel injector flow drift, injector opening dynamics, and pressure regulation errors may result in disproportionately different fueling errors at different engine speeds and engine loads. For example, fuel injector flow drift due to deposits or wear may result in a higher percentage of fueling deviation at low injection quantities, which correspond to low engine loads, compared to fueling deviation at high injection quantities, which correspond to high engine loads. Similarly, pressure regulation deviation may have different effects on fuel delivery at different engine speeds due to dynamic pressure variations in the fuel supply subsystem. By performing the adaptive fuel learning independently across multiple engine speed–load regions, the engine control unit 146 accurately captures these non-linear, operating-region-dependent deviations and stores distinct adaptive fuel correction values for different combinations of engine speed and engine load. The operating-region-specific adaptive fuel learning at step 420 corresponds to the feature as discussed, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map, and wherein the adaptive fuel learning is executed independently across multiple engine speed–load regions to compensate for non-linear injector flow deviation and pressure regulation drift.
At step 422, the engine control unit 146 executes an update step, wherein the adaptive fuel correction value derived at step 420 is stored in the two-dimensional adaptive fuel learning map 206 at the region corresponding to the identified engine speed and engine load. The engine control unit 146 updates the adaptive fuel correction value for the identified region of the two-dimensional adaptive fuel learning map 206, replacing or incrementally adjusting the previously stored adaptive fuel correction value for that region. The updated adaptive fuel correction value is used by the engine control unit 146 in subsequent engine control cycles when the internal combustion engine operates at the same or a similar combination of engine speed and engine load, providing feed-forward compensation for the learned fuel delivery deviation in addition to the short-term closed-loop fuel correction.
At step 422, the engine control unit 146 further stores the updated adaptive fuel correction value in the non-volatile memory 204. The storage of the adaptive fuel correction value in the non-volatile memory 204 ensures that the learned adaptive fuel correction value is retained across successive engine start and engine stop cycles of the internal combustion engine. When the engine control unit 146 is powered off during an engine stop cycle, the adaptive fuel correction value stored in the non-volatile memory 204 is preserved. Upon a subsequent engine start cycle, the engine control unit 146 retrieves the stored adaptive fuel correction value from the non-volatile memory 204, as described at step 402, and applies the stored adaptive fuel correction value to the fuel injection commands. This retention of the adaptive fuel correction value across successive engine start and engine stop cycles eliminates the need for a new learning cycle upon each engine start, reduces transient deviation between the received air–fuel ratio signal and the target air–fuel ratio during engine start, and enables immediate stabilization of the air–fuel ratio.
The adaptive fuel learning process implemented at steps 418 through 422 is performed continuously during engine operation whenever the predefined fuel learning conditions are satisfied. The engine control unit 146 repeatedly derives and updates the adaptive fuel correction values for different regions of the two-dimensional adaptive fuel learning map 206 as the internal combustion engine traverses different combinations of engine speed and engine load during normal driving. Over time, the two-dimensional adaptive fuel learning map 206 accumulates adaptive fuel correction values across the entire operating range of the internal combustion engine, providing operating-region-specific feed-forward compensation that covers the full engine operating domain. The continuous learning process enables the engine control unit 146 to track and adapt to gradual changes in fuel composition, for example when the vehicle is refueled with a different source of gaseous fuel, as well as gradual changes in fuel injector flow characteristics, for example due to progressive fuel injector flow drift occurring over the useful life of the internal combustion engine.
At step 424, a further decision step is executed by the engine control unit 146 to determine whether the magnitude of the adaptive fuel correction value exceeds the predefined threshold. The engine control unit 146 evaluates the magnitude of the adaptive fuel correction value, which may be expressed as an absolute value or a percentage correction relative to the base fuel injection quantity from the feed-forward fuel map 208, against the predefined threshold. The predefined threshold is a predetermined value that is calibrated to distinguish between normal fuel composition variations, which require fuel injection correction but do not indicate inferior fuel quality, and larger fuel composition deviations, which are indicative of inferior fuel quality, abnormal combustion characteristics, or conditions requiring ignition timing correction. Exceeding the predefined threshold is indicative of conditions such as low fuel calorific value, high inert content in the gaseous fuel, slow flame propagation speed, or reduced knock margin, which may arise when the internal combustion engine is operated on gaseous fuel having inferior or abnormal characteristics.
In one or more embodiments, different ranges of the magnitude of the adaptive fuel correction value correspond to different inferred fuel quality states. The engine control unit 146 classifies the fuel quality based on the magnitude of the adaptive fuel correction value, wherein a magnitude within a first range below the predefined threshold corresponds to a normal fuel quality state, a magnitude within a second range exceeding the predefined threshold by a first amount corresponds to a moderately degraded fuel quality state, and a magnitude within a third range exceeding the predefined threshold by a larger amount corresponds to a significantly degraded fuel quality state. This classification of fuel quality states based on the magnitude of the adaptive fuel correction value enables the engine control unit 146 to infer the fuel quality without use of a direct fuel composition sensor.
If the magnitude of the adaptive fuel correction value does not exceed the predefined threshold at step 424, the method 400 proceeds to step 426. At step 426, the engine control unit 146 commands the ignition system 174 to maintain the base ignition timing based on the feed-forward ignition timing map 210. When the magnitude of the adaptive fuel correction value is within the normal range and does not exceed the predefined threshold, the engine control unit 146 determines that the fuel quality is within acceptable limits and that no ignition timing correction is required to mitigate abnormal combustion risks. Accordingly, the engine control unit 146 outputs the ignition command to the ignition system 174 based on the base ignition timing determined from the feed-forward ignition timing map 210 at step 406, and the ignition system 174 initiates combustion at the base ignition timing.
If the magnitude of the adaptive fuel correction value exceeds the predefined threshold at step 424, the method 400 proceeds to step 428. At step 428, the engine control unit 146 commands the ignition system 174 to retard the ignition timing relative to the base ignition timing. The engine control unit 146 outputs an ignition command to the ignition system 174 that specifies an ignition timing that is later, or retarded, relative to the base ignition timing determined from the feed-forward ignition timing map 210. The retarding of the ignition timing delays the point in time during the engine cycle at which the spark plug 118 produces the spark discharge, such that combustion is initiated later in the compression stroke or early in the expansion stroke. The retarding of the ignition timing reduces the peak combustion pressure within the combustion chamber 106, suppresses knock and abnormal combustion that may arise from inferior gaseous fuel characteristics, lowers thermal stress on engine components including the piston 104, the cylinder head 102, and the spark plug 118, and shifts engine operation into a safe and stable combustion zone.
In one or more embodiments, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the engine control unit 146 commands the ignition system 174 to retard the ignition timing by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold. The proportional relationship between the ignition timing retard and the difference between the magnitude and the predefined threshold provides a graduated ignition timing correction that is commensurate with the severity of the inferred fuel quality degradation. When the magnitude of the adaptive fuel correction value exceeds the predefined threshold by a small amount, the engine control unit 146 applies a small ignition timing retard. When the magnitude of the adaptive fuel correction value exceeds the predefined threshold by a large amount, indicating a more significant fuel quality degradation, the engine control unit 146 applies a larger ignition timing retard. This proportional ignition timing retard ensures that the ignition timing correction is sufficient to mitigate abnormal combustion risks while minimizing unnecessary reduction in engine performance and thermal efficiency.
The commanding of the ignition system 174 to retard the ignition timing at step 428 is executed by the engine control unit 146 automatically and without reliance on a knock sensor or a direct fuel composition sensor. The engine control unit 146 infers the presence of inferior or abnormal fuel characteristics from the magnitude of the adaptive fuel correction value exceeding the predefined threshold, and the engine control unit 146 pre-emptively applies the ignition timing retard to mitigate abnormal combustion risks before any knock or detonation event occurs. This pre-emptive approach differs from conventional knock-sensor-based ignition timing control, in which the engine control unit detects a knock event only after the knock event has already occurred and then reactively retards the ignition timing.
At step 430, the engine control unit 146 updates the feed-forward fuel map 208 with the adaptive fuel correction value for use in generating subsequent base fuel injection commands. The engine control unit 146 incorporates the learned adaptive fuel correction value into the feed-forward fuel map 208 such that subsequent base fuel injection commands generated from the feed-forward fuel map 208 reflect the learned fuel delivery deviation. This updating of the feed-forward fuel map 208 with the adaptive fuel correction value is performed for the region of the feed-forward fuel map 208 corresponding to the current engine speed and engine load. The updating at step 430 provides a feed-forward compensation mechanism that anticipates the fuel delivery deviation and incorporates the learned correction into the base fuel injection command, thereby reducing the magnitude of the closed-loop fuel correction required at step 416 and improving the speed and accuracy of the air–fuel ratio control.
The updating of the feed-forward fuel map 208 at step 430 is complementary to the storage of the adaptive fuel correction value in the two-dimensional adaptive fuel learning map 206 at step 422. While the two-dimensional adaptive fuel learning map 206 stores the adaptive fuel correction values separately from the feed-forward fuel map 208, the updating at step 430 integrates the learned correction into the feed-forward path such that the engine control unit 146 generates base fuel injection commands that are closer to the correct fuel delivery requirement from the outset. Over repeated learning cycles, the feed-forward fuel map 208 is progressively refined to reflect the actual fuel composition and fuel injector flow characteristics encountered during operation of the internal combustion engine.
At step 432, the engine control unit 146 continues operation of the internal combustion engine with the updated fuel injection and ignition timing control parameters. The engine control unit 146 applies the updated base fuel injection command, as adjusted by the adaptive fuel correction value, to command the at least one gaseous fuel injector 128. The engine control unit 146 applies the ignition timing, either the base ignition timing from the feed-forward ignition timing map 210 if the magnitude of the adaptive fuel correction value did not exceed the predefined threshold, or the retarded ignition timing if the magnitude of the adaptive fuel correction value exceeded the predefined threshold, to command the ignition system 174.
At step 434, the method 400 returns to the start of the control loop at step 402, and the method 400 is continuously and cyclically executed throughout engine operation. The continuous and cyclic execution of the method 400 ensures that the engine control unit 146 continuously acquires the engine operating parameters, generates the base fuel injection command, commands the at least one gaseous fuel injector 128, receives the air–fuel ratio signal from the exhaust gas sensor 158, computes the deviation, applies the closed-loop fuel correction, derives and updates the adaptive fuel correction value when the predefined fuel learning conditions are satisfied, determines whether the magnitude of the adaptive fuel correction value exceeds the predefined threshold, and commands the ignition system 174 accordingly.
The adaptive fuel learning and adaptation implemented in the method 400 operates in a manner analogous to intelligence–based learning systems, wherein observed feedback signals, specifically the air–fuel ratio signal from the exhaust gas sensor 158, are continuously evaluated, patterns in the air–fuel ratio deviation are identified, and corrective actions in the form of the adaptive fuel correction value are updated in real time. The learning rate and the implementation speed of the adaptive fuel injection and ignition control are configured such that accurate fuel injection corrections and ignition timing corrections are established within a predefined time period following a change in fuel composition. In one or more embodiments, the adaptive fuel learning converges to a stable adaptive fuel correction value within a matter of seconds following a change in fuel composition. This rapid convergence is enabled by the wideband-type lambda sensor, which is configured to measure the air–fuel ratio over a range extending from lean conditions to rich conditions, and which provides the engine control unit 146 with an accurate air–fuel ratio signal even for large deviations in fuel characteristics.
The adaptive fuel correction value derived and stored by the engine control unit 146, as described with reference to FIGS. 3 and 4, inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor. Because the adaptive fuel correction value is derived based on the deviation between the received air–fuel ratio signal and the target air–fuel ratio, the adaptive fuel correction value inherently captures any factor that causes a discrepancy between the expected fuel delivery and the actual fuel delivery, regardless of whether the discrepancy arises from fuel composition variability, change in fuel calorific value, fuel injector flow drift, pressure regulation deviation, or any combination of these factors. The engine control unit 146 does not require knowledge of the specific fuel composition or the specific fuel calorific value to derive the adaptive fuel correction value. Instead, the adaptive fuel correction value is derived from the observable effect of the fuel delivery discrepancy on the air–fuel ratio, as measured by the exhaust gas sensor 158. This approach eliminates the need for a direct fuel composition sensor, which is not commercially available in an automotive-grade form suitable for real-time measurement of gaseous fuel composition under vehicle operating conditions.
Similarly, the commanding of the ignition system 174 to retard the ignition timing when the magnitude of the adaptive fuel correction value exceeds the predefined threshold is executed by the engine control unit 146 without reliance on a knock sensor. The engine control unit 146 infers the presence of inferior fuel quality or abnormal combustion characteristics from the magnitude of the adaptive fuel correction value, and the engine control unit 146 pre-emptively retards the ignition timing to mitigate abnormal combustion risks without waiting for a knock event to occur and without relying on a knock sensor to detect the knock event. This approach provides a pre-emptive and proactive ignition timing correction that protects engine hardware from damage due to knock and detonation, rather than a reactive correction that responds only after a knock event has already occurred.
The adaptive fuel correction value compensates for fuel composition variability across a plurality of gaseous fuel types including at least two of compressed natural gas (CNG), liquefied natural gas (LNG), biogas, compressed biogas (CBG), hydrogen-enriched natural gas (HCNG), and mixtures thereof. When the internal combustion engine is fueled with different gaseous fuel types, the fuel composition, the fuel calorific value, and the stoichiometric air–fuel ratio of the gaseous fuel may vary significantly. For example, compressed natural gas (CNG) sourced from different geographical regions may vary in methane concentration and may contain varying proportions of higher hydrocarbons such as ethane, propane, and butane, as well as inert or diluent gases including carbon dioxide and nitrogen. Compressed biogas (CBG), which is produced from diverse biological feedstocks and production pathways, may exhibit significant variation in calorific value and inert content compared to conventional compressed natural gas. Hydrogen-enriched natural gas (HCNG), which is a mixture of natural gas and hydrogen, has different combustion characteristics compared to conventional compressed natural gas due to the higher flame speed and lower volumetric energy density of hydrogen. When the internal combustion engine is operated on any of these gaseous fuel types, or on mixtures thereof, the adaptive fuel correction value derived by the engine control unit 146 automatically compensates for the deviation in fuel delivery caused by the different fuel composition, without requiring the engine control unit 146 to identify the specific gaseous fuel type or to employ a direct fuel composition sensor.
The adaptive fuel correction value further compensates for progressive fuel injector flow drift occurring over the useful life of the internal combustion engine. Over the useful life of the internal combustion engine, the flow characteristics of the at least one gaseous fuel injector 128 may change due to deposits, contamination, wear, or changes in opening dynamics. These changes in fuel injector flow characteristics cause the actual fuel delivery to deviate from the expected fuel delivery assumed in the feed-forward fuel map 208. The adaptive fuel learning process implemented in the method 400, by continuously deriving and updating the adaptive fuel correction values in the two-dimensional adaptive fuel learning map 206, tracks and compensates for these gradual changes in fuel injector flow characteristics over the useful life of the internal combustion engine. The continuous learning process ensures that the fuel injection commands remain accurate despite the progressive fuel injector flow drift, thereby maintaining the air–fuel ratio within the narrow stoichiometric window required for high conversion efficiency of the catalytic converter 160 throughout the useful life of the internal combustion engine.
The adaptive fuel injection and ignition control disclosed herein maintains the air–fuel ratio control during transient engine operation encountered under real driving emission conditions. Real driving emission conditions involve uncontrolled variables such as commercial fuel variability, altitude changes, cold and hot ambient conditions, humidity variation, and varying driving patterns that are not encountered during laboratory-based emission testing. During real driving emission conditions, the internal combustion engine traverses various combinations of engine speed and engine load in rapid succession, and the fuel delivery requirements change dynamically. The adaptive fuel correction values stored in the two-dimensional adaptive fuel learning map 206 provide operating-region-specific feed-forward compensation that enables the engine control unit 146 to anticipate and correct the fuel delivery deviation at each combination of engine speed and engine load, thereby reducing the air–fuel ratio deviation during transient engine operation. The continuous and cyclic execution of the method 400 ensures that the adaptive fuel correction values are continuously updated as the internal combustion engine operates under real driving emission conditions, and the stored adaptive fuel correction values provide immediate compensation without requiring a new learning cycle at each operating point.
The adaptive fuel injection and ignition control disclosed herein maintains emission compliance under real driving emission conditions throughout a defined useful life of the vehicle. The defined useful life of the vehicle is specified by applicable regulatory requirements, for example as mandated under Real Driving Emission (RDE) regulations. Throughout the defined useful life, the internal combustion engine is subject to the cumulative effects of fuel composition variability, fuel injector flow drift, pressure regulation deviation, and aging of other fuel system components. The adaptive fuel learning process implemented in the method 400, by continuously deriving, updating, and storing the adaptive fuel correction values in the non-volatile memory 204, compensates for these cumulative effects throughout the defined useful life. By maintaining the air–fuel ratio within the narrow stoichiometric window required for high conversion efficiency of the catalytic converter 160, the adaptive fuel injection and ignition control ensures that the tailpipe emissions of the internal combustion engine remain within the limits specified by the applicable emission regulations throughout the defined useful life of the vehicle, even under real driving emission conditions.
The adaptive fuel injection and ignition control disclosed herein provides the following technical effects and advantages. By deriving the adaptive fuel correction value and applying the adaptive fuel correction value to adjust the fuel injection commands, the engine control unit 146 maintains the air–fuel ratio of the combusted gases at or near the stoichiometric air–fuel ratio, as illustrated in FIG. 5, thereby preserving the high conversion efficiency of the catalytic converter 160 for all three regulated exhaust gas constituents, namely nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC). By storing the adaptive fuel correction values in the two-dimensional adaptive fuel learning map 206 indexed by the engine speed and the engine load, the engine control unit 146 provides operating-region-specific compensation that accounts for non-linear and operating-point-dependent fuel delivery deviations, resulting in more accurate air–fuel ratio control across the entire operating range of the internal combustion engine compared to conventional single global fuel trim approaches.
By storing the adaptive fuel correction values in the non-volatile memory 204 and retaining the stored adaptive fuel correction values across successive engine start and engine stop cycles, the engine control unit 146 enables immediate stabilization of the air–fuel ratio upon engine start without requiring a new learning cycle, thereby reducing transient air–fuel ratio deviations and emission excursions during engine start. By determining whether the magnitude of the adaptive fuel correction value exceeds the predefined threshold and commanding the ignition system 174 to retard the ignition timing when the predefined threshold is exceeded, the engine control unit 146 pre-emptively mitigates abnormal combustion risks, including knock and detonation, without reliance on a knock sensor or a direct fuel composition sensor. The autonomous ignition timing retard protects engine hardware from damage, maintains combustion stability, and reduces thermal stress on engine components.
By compensating for fuel composition variability across multiple gaseous fuel types without use of a direct fuel composition sensor, the adaptive fuel injection and ignition control eliminates the need for costly and impractical fuel composition sensors. By compensating for progressive fuel injector flow drift over the useful life of the internal combustion engine, the adaptive fuel injection and ignition control maintains accurate fuel metering without requiring injector recalibration or replacement. By maintaining the air–fuel ratio within the narrow stoichiometric window required for high conversion efficiency of the catalytic converter 160, the adaptive fuel injection and ignition control reduces the need for oversized catalytic converters with excessive precious metal loading, thereby reducing vehicle cost and reducing reliance on supply-constrained platinum group metals. By maintaining emission compliance under real driving emission conditions throughout the defined useful life of the vehicle, the adaptive fuel injection and ignition control provides sustained real-world emission performance that meets regulatory requirements.
While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those embodiments. In view of the present invention, many modifications and variations may be present themselves, to those skilled in the art without departing from the scope of the various embodiments of the present invention, as described herein. The scope of the present invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.  , Claims:PATENT CLAIMS
1. A system for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, the system comprising:
an engine control unit communicatively coupled to at least one gaseous fuel injector, an ignition system, and an exhaust gas sensor positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine;
wherein the engine control unit is configured to:
acquire a plurality of engine operating parameters including at least engine speed and engine load;
generate a base fuel injection command based on a feed-forward fuel map and the acquired engine operating parameters;
command the at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine based on the base fuel injection command;
receive an air–fuel ratio signal from the exhaust gas sensor indicative of an air–fuel ratio of combusted gases;
compute a deviation between the received air–fuel ratio signal and a target air–fuel ratio;
derive an adaptive fuel correction value based on the computed deviation;
apply the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio;
determine whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold; and
upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, command the ignition system to retard an ignition timing relative to a base ignition timing.

2. The system as claimed in claim 1, wherein the engine control unit is further configured to store the adaptive fuel correction value in a two-dimensional adaptive fuel learning map indexed by the engine speed and the engine load, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map.

3. The system as claimed in claim 1, wherein the engine control unit is configured to derive the adaptive fuel correction value based on the computed deviation in combination with historical injector opening duration data associated with the at least one gaseous fuel injector, and wherein the engine control unit derives the adaptive fuel correction value when predefined fuel learning conditions are satisfied, the predefined fuel learning conditions including at least one of: steady-state operation of the internal combustion engine, absence of knock in the internal combustion engine, validity of sensor signals associated with the internal combustion engine, and operation of the internal combustion engine within predefined temperature ranges.

4. The system as claimed in claim 1, wherein, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the engine control unit commands the ignition system to retard the ignition timing by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold.

5. The system as claimed in claim 1, further comprising a non-volatile memory communicatively coupled to the engine control unit, wherein the engine control unit is configured to:
store the adaptive fuel correction value in the non-volatile memory;
retain the stored adaptive fuel correction value in the non-volatile memory across successive engine start and engine stop cycles of the internal combustion engine; and
apply the stored adaptive fuel correction value to the fuel injection commands upon a subsequent engine start to reduce transient deviation between the received air–fuel ratio signal and the target air–fuel ratio.

6. The system as claimed in claim 1, wherein the exhaust gas sensor is a wideband-type lambda sensor configured to measure the air–fuel ratio of the combusted gases over a range extending from lean conditions to rich conditions, wherein the target air–fuel ratio is a stoichiometric air–fuel ratio, and wherein the catalytic converter is a three-way catalytic converter configured to simultaneously convert nitrogen oxides, carbon monoxide, and unburned hydrocarbons present in the combusted gases.

7. The system as claimed in claim 1, wherein the adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor, and wherein the engine control unit commands the ignition system to retard the ignition timing without reliance on a knock sensor.

8. The system as claimed in claim 1, wherein the adaptive fuel correction value compensates for fuel composition variability across a plurality of gaseous fuel types including at least two of: compressed natural gas, liquefied natural gas, biogas, compressed biogas, hydrogen-enriched natural gas, and mixtures thereof, and wherein the adaptive fuel correction value further compensates for progressive fuel injector flow drift occurring over a useful life of the internal combustion engine.

9. A method for adaptive fuel injection and ignition control in an internal combustion engine configured for operation on gaseous fuel, the method comprising:
commanding at least one gaseous fuel injector to inject a quantity of gaseous fuel into a combustion chamber of the internal combustion engine;
receiving an air–fuel ratio signal from an exhaust gas sensor positioned upstream of a catalytic converter in an exhaust system of the internal combustion engine;
deriving an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio;
applying the adaptive fuel correction value to adjust subsequent fuel injection commands to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio;
determining whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold; and
upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, commanding an ignition system to retard an ignition timing relative to a base ignition timing.

10. The method as claimed in claim 9, further comprising:
acquiring a plurality of engine operating parameters including at least engine speed and engine load; and
storing the adaptive fuel correction value in a two-dimensional adaptive fuel learning map indexed by the engine speed and the engine load, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map.

11. The method as claimed in claim 9, further comprising:
storing the adaptive fuel correction value in a non-volatile memory; and
applying the stored adaptive fuel correction value to the fuel injection commands upon a subsequent engine start of the internal combustion engine to reduce transient deviation between the received air–fuel ratio signal and the target air–fuel ratio.

12. The method as claimed in claim 9, wherein different ranges of the magnitude of the adaptive fuel correction value correspond to different inferred fuel quality states, and wherein, upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, the ignition timing is retarded by an amount that is proportional to a difference between the magnitude of the adaptive fuel correction value and the predefined threshold.

13. The method as claimed in claim 9, further comprising:
generating a base fuel injection command based on a feed-forward fuel map and at least engine speed and engine load of the internal combustion engine prior to commanding the at least one gaseous fuel injector; and
updating the feed-forward fuel map with the adaptive fuel correction value for use in generating subsequent base fuel injection commands;
wherein the method is continuously and cyclically executed during operation of the internal combustion engine.

14. An engine control unit for controlling an internal combustion engine operating on gaseous fuel, the engine control unit comprising:
one or more processing units; and
a memory unit communicatively coupled to the one or more processing units, the memory unit storing machine-readable instructions that, when executed by the one or more processing units, cause the engine control unit to:
receive an air–fuel ratio signal from an exhaust gas sensor indicative of an air–fuel ratio of combusted gases in the internal combustion engine;
derive an adaptive fuel correction value based on a deviation between the received air–fuel ratio signal and a target air–fuel ratio;
output a fuel injection command adjusted by the adaptive fuel correction value to reduce the deviation between the received air–fuel ratio signal and the target air–fuel ratio;
determine whether a magnitude of the adaptive fuel correction value exceeds a predefined threshold; and
upon determining that the magnitude of the adaptive fuel correction value exceeds the predefined threshold, output an ignition command to retard an ignition timing relative to a base ignition timing.

15. The engine control unit as claimed in claim 14, wherein the memory unit further stores a two-dimensional adaptive fuel learning map indexed by engine speed and engine load of the internal combustion engine, and wherein the machine-readable instructions, when executed by the one or more processing units, further cause the engine control unit to:
store the adaptive fuel correction value in the two-dimensional adaptive fuel learning map, wherein the adaptive fuel correction value is updated independently for each region of the two-dimensional adaptive fuel learning map; and
retain the stored adaptive fuel correction value in the memory unit across successive engine start and engine stop cycles of the internal combustion engine;
wherein the adaptive fuel correction value inherently compensates for variations in at least one of fuel composition, fuel calorific value, and fuel injector flow characteristics without use of a direct fuel composition sensor.