TECHNICAL FIELD
[001] Embodiments disclosed herein relate to vehicles with a dual fuel engine, and more particularly to controlling fuel flow in a vehicle with a dual fuel engine.
BACKGROUND
[002] Generally, a vehicle associated with a dual-fuel engine runs on two different fuels to reduce emissions and improve operating economy. The dual-fuel engine includes a Compression-Ignited (CI) engine which operates on primary fuels (petro-diesel, bio-diesel and so on). The alternative fuels for the CI engine can be gaseous fuels (Compressed Natural Gas (CNG), Liquefied Petroleum Gas (LPG) and so on). Further, the primary fuels can be injected into a combustion chamber directly and the gaseous fuels can be inducted into a manifold with air or directly into cylinder. The inducted gaseous fuels result in reduction in the flow of the primary fuels depending on the current operating zone of the engine.
[003] The dual-fuel engine may include a mechanical fuel injection pump to control the flow of the fuels. In conventional approaches, variables such as, a position of a control lever of the mechanical fuel injection pump and an engine operating speed can be used to map the flow of the gaseous fuel flow. However, the position of the control lever can be approximately the same operating angle for different revolutions per minute (rpm) around the same load points which limits flexibility in controlling the flow of gaseous fuel at different operating load points of the engine/vehicle. Also, the operating load points cannot be interpreted from the operating angle of the control lever of the mechanical fuel injection pump. In addition, because of the position of the control lever, the overall fuel efficiency drops and creates a negative impact on the emissions.

OBJECTS
[004] The principal object of embodiments herein is to disclose methods and systems for controlling flow of a gaseous fuel to a dual-fuel engine in a vehicle for different operating load points and engine operating speeds.
[005] Another object of embodiments herein is to disclose a method for calculating an operating load point based on an exhaust gas temperature.
[006] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating at least one embodiment and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[007] Embodiments herein are illustrated in the accompanying drawings, through out which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[008] FIG. 1 illustrates a control system for controlling a fuel flow in a vehicle with a dual fuel engine, according to embodiments as disclosed herein;
[009] FIG. 2 illustrates an example layout of a dual fuel system of a vehicle, according to embodiments as disclosed herein;

[0010] FIG. 3 is a flow diagram illustrating a method for controlling fuel flow in a vehicle with a dual fuel engine, according to embodiments as disclosed herein; and
[0011] FIG. 4 is an example flow diagram illustrating a method for controlling fuel flow in a vehicle with a dual fuel engine based on an exhaust gas temperature, according to embodiments as disclosed herein.

DETAILED DESCRIPTION
[0012] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0013] Embodiments herein disclose methods and systems for controlling a fuel flow in a vehicle with a dual-fuel engine based on an exhaust gas temperature. Referring now to the drawings, and more particularly to FIGS. 1 through 4, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.
[0014] FIG. 1 illustrates a control system 102 for controlling a fuel flow in a vehicle 100 with a dual fuel engine 202, according to embodiments as disclosed herein. The vehicle 100 with the dual fuel engine 202 can be capable of running on two fuels. Examples of the vehicle 100 can be, but is not limited to, cars, motor vehicles, two wheeled vehicles, three wheeled vehicles, work machines, marine engines, farm implements (such as tractors, threshers, and so on) or any other vehicles that require electrical power generators. The dual fuel engine 202 herein refers to an engine capable of operating in a dual fuel mode, when the engine runs on two different fuels. The dual fuel engine 202 operates on at least one of a Spark-Ignited (SI) and a Compressing-Ignited (CI) engine fuel. A primary fuel of the dual-fuel engine 202 can be, but not limited to, petroleum diesel, bio-fuel, gas oil, bio-diesel and so on. The primary fuel can be a pilot fuel which can be injected into a combustion chamber directly. The secondary fuel is a gaseous fuel.

Examples of the gaseous fuel can be, but not limited to, Compressed Natural Gas (CNG), Liquefied Natural Gas (LPG), Liquefied Natural Gas (LNG), propane, hydrogen, and so on. The gaseous fuel can be a primary fuel which can be inducted into a manifold with air, wherein the mixture of the gaseous fuel and air may be compressed in a cylinder. Further, the primary fuel may act as an igniter for the gaseous fuel inside the combustion chamber of the dual-fuel engine 202. As the amount of gaseous fuel injected into the cylinder increases, consumption of the liquid fuel can be reduced.
[0015] The control system 102 can be mounted on the vehicle 100 at any suitable position. The control system 102 includes a measuring module 104, a control unit 106 and a memory 108. In an embodiment, the control unit 106 includes a processor, a micro-controller, a memory, a storage unit, an input output unit, a display unit and so on. In an embodiment herein, the control unit 106 can be a dedicated control unit. In an embodiment herein, the control unit 106 can be an electronic control unit present in the vehicle, which performs other functions related to the vehicle or one or more systems/sensors/modules present in the vehicle, other than according to embodiments as disclosed herein. The control unit 106 can be communicatively coupled to the measuring module 104 and the memory 108 through a communication network. Examples of the communication network can be, but not limited to, at least one of the Internet, a wired network (a Local Area Network (LAN), a Controller Area Network (CAN) network, a bus network, Ethernet and so on), a wireless network (a Wi-Fi network, a cellular network, a Wi-Fi Hotspot, Bluetooth, Zigbee and so on) and so on. The control system 102 may also include or have access to memory 108/databases (not shown) which include at least one of lookup tables providing information about requirement of fuel flow at different operating load points and engine operating speed, pre-defined exhaust temperature values and corresponding operating load points and so on.
[0016] The measuring module 104 can be configured to measure operating parameters of the dual-fuel engine 202. The operating parameters can be, but not

limited to, engine operating speed (in rpm (revolution per minute)), exhaust gas temperature, current flow of the at least one of the primary fuel and the gaseous fuel and so on. The measuring module 104 can use at least one sensor to measure the operating parameters of the dual-fuel engine. Examples of the sensors can be, but is not limited to, a temperature sensor, a thermocouple, a speed sensor, a tachometer and so on. In an embodiment, a Variable Reluctance (VR) sensor can be used for measuring the engine operating speed. In another embodiment, Resistance Temperature Detectors (RTD) can be used for measuring the exhaust gas temperature. However, it is also within the scope of the embodiments disclosed herein to use any type of sensors without otherwise deterring the intended function of measuring the operating parameters of the dual-fuel engine as can be deduced from this description and corresponding drawings. The measuring module 104 can communicate the measured operating parameters to the control unit 106 through the communication network.
[0017] The control unit 106 can be configured to control flow of the gaseous fuel to the dual-fuel engine 202 based on the measured operating parameters. On receiving the operating parameters of the dual-fuel engine 202, the control unit 106 uses the exhaust gas temperature to calculate an operating load point (a load point at which the engine operates). The control unit 106 checks if the measured exhaust gas temperature is between first pre-defined value(s) and second pre-defined value(s). The first and second pre-defined values may be pre-defined exhaust gas temperature values. On determining that the measured exhaust gas temperature is between the first pre-defined value and the second pre-defined value, the control unit 106 selects the operating load point (a load point at which the engine operates) associated with the combination of the first and second pre-defined values. Thus, the operating load point can be selected based on the exhaust gas temperature.
[0018] Once the operating load point is selected, the control unit 106 compares the exhaust gas temperature with an ideal temperature value stored in the look-up table (stored in the database/memory 108). The ideal temperature may

be the exhaust gas temperature observed during required flow of the gaseous fuel for the calculated operating load point and the engine operating speed. The control unit 106 calculates a temperature difference between the exhaust temperature and the ideal temperature.
[0019] Based on the calculated temperature difference, the control unit 106 determines the rate of flow of the gaseous fuel to the dual-fuel engine 202 for the calculated operating load point and the engine operating speed. Accordingly, the control unit 106 controls the rate of the flow of the gaseous fuel to the dual fuel engine 202. In an embodiment, the control unit 106 increases the flow of the gaseous fuel on determining that the temperature difference calculated with respect to the look-up table is positive. In another embodiment, the control unit 106 decreases the flow of the gaseous fuel on determining that the temperature difference calculated with respect to the look-up table is negative. In yet another embodiment, the control unit 106 maintains the same flow of the gaseous fuel on determining that the temperature difference computed with respect to the look-up table is zero. Thus, the flow of the gaseous fuel can be controlled to reach an optimum operating exhaust gas temperature which in turn improves fuel substitution rate and overall fuel consumption and reduces emissions.
[0020] The memory 108 can be configured to store the measured operating parameters of the dual-fuel engine, the operating load points and so on. The memory 108 can be may include one or more computer-readable storage media. The memory 108 may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the memory 108 may, in some examples, be considered as non-transitory storage medium. The term “non-transitory” may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term “non-transitory” should not be interpreted to mean that the memory 108 is non-movable. In some examples, the memory 108 can be configured to store larger

amounts of information than the memory. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in Random Access Memory (RAM) or cache).
[0021] FIG. 1 shows exemplary units of the control system 102, but it is to be understood that other embodiments are not limited thereon. In other embodiments, the control system 102 may include less or more number of units. Further, the labels or names of the units are used only for illustrative purpose and does not limit the scope of the embodiments herein. One or more units can be combined together to perform same or substantially similar function in the control system 102.
[0022] FIG. 2 illustrates an example layout of a dual fuel system 200 of the vehicle 100, according to embodiments as disclosed herein. The dual fuel system 200 includes the dual-fuel engine 202 which may include at least one of the SI engine, the CI engine, an internal combustion engine and so on. The dual fuel engine 202 can be configured to combust a mixture of air, the primary/liquid fuel and/or the gaseous fuel. Embodiments herein are further explained considering that the dual fuel engine 202 includes the CI engine and further the diesel and the CNG as examples for the primary fuel and the gaseous fuel of the CI engine respectively, but it may be obvious to a person of ordinary skill in the art that any other liquid and gaseous fuel can be considered.
[0023] The dual-fuel engine 202 can be connected to a diesel fuel tank 204 through a diesel fuel system 206. The diesel fuel system 206 may include a diesel fuel pump 206a and a diesel fuel filter 206b. The diesel fuel pump 206a may be provided in a diesel fuel line to pressurize and force the diesel through the diesel fuel line. The diesel fuel system 206 may include multiple injectors coupled to the diesel fuel line which inject the diesel directly into a combustion chamber (not shown) associated with a fuel injector 208. Further, the diesel fuel system 206 may be connected with an accelerator/pedal 210 and the fuel injector 208.
[0024] The dual-fuel engine 202 includes at least one cylinder 212a-212n containing the CNG. A valve of each cylinder may be connected to a CNG filling

valve with pressure gauge 214. The CNG from the CNG filling valve with the pressure gauge 214 can be provided to a CNG pressure regulator 216 by a CNG high pressure line. The CNG pressure regulator 216 controls an input pressure of the received CNG from the CNG filling valve with the pressure gauge 214. Further, the CNG from the pressure regulator 216 can be provided to a low pressure CNG filter 218 which filters the CNG at low pressure. The filtered CNG can be provided to a flow control value 220 associated with the fuel injector 208 through a CNG low pressure line. The fuel injector 208 may inject the CNG into the combustion chamber based on an electronic control unit signal (ECU) generated by the control unit 106.
[0025] The control unit 106 receives the measured operating parameters such as the engine operating speed, the exhaust temperature, current CNG pressure, the current flow of the CNG and so on. The control unit 106 further calculates the operating load point using the exhaust gas temperature. Once the operating load point is calculated, the control unit 106 controls the flow of the CNG to the fuel injector 208 by generating the ECU for at least one of the flow control valve 220 and the fuel injector 208. In an embodiment, the ECU signal generated for the fuel control valve 220 may be ON/OFF signal for controlling the flow of the CNG from the at least one CNG cylinder 212a-212n to the fuel injector 208. In another embodiment, the ECU signal may comprise at least one of continuous variable voltage, current, pulse width, desired flow rate (increased/reduced flow rate) and so on for controlling the flow of the CNG to the fuel injector 208. Thus, improving fuel substitution rate and overall fuel economy.
[0026] FIG. 3 is a flow diagram illustrating a method for controlling the fuel flow in the vehicle 100 with the dual fuel engine 202, according to embodiments as disclosed herein.
[0027] At step 302, the method includes measuring, by the measuring module 104, the operating parameters of the dual-fuel engine. The operating parameters can be the engine operating speed in rpm, the exhaust temperature and so on. At step 304, the method includes calculating, by the control unit 106, the operating load point based on the measured exhaust gas temperature. The control

unit 106 compares if the measured exhaust gas temperature is between the first and the second pre-defined temperature values. The control unit 106 selects the operating load point associated with the combination of the first and second pre-defined temperature values.
[0028] At step 306, the method includes controlling, by the control unit 106, the flow of the gaseous fuel to the dual-fuel engine according to the calculated operating load point and the engine operating speed. The control unit 106 compares the exhaust gas temperature with the ideal temperature stored in the look-up table. The ideal temperature may be the exhaust gas temperature observed during the optimal flow of the gaseous fuel for the calculated at least one operating load point and the engine operating speed. Further, the control unit 106 calculates the temperature difference between the measured exhaust gas temperature and the ideal temperature. Based on the temperature difference, the control unit 106 controls the flow of the gaseous fuel to the dual-fuel engine 202.
[0029] The various actions, acts, blocks, steps, or the like in the method and the flow diagram 300 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.
[0030] FIG. 4 is an example flow diagram illustrating a method for controlling the fuel flow in the vehicle 100 with the dual fuel engine 202 based on the exhaust gas temperature, according to embodiments as disclosed herein. As illustrated in FIG.4, the measuring module 104 measures the engine operating speed in rpm, the fuel flow (flow of the gaseous fuel) and the exhaust gas temperature. For example, the measured engine operating speed may be ‘ALPHA’ rpm, the gaseous fuel flow may be ‘BETA’ Kg/h and the exhaust gas temperature may be ‘GAMMA’ ºC.
[0031] The control unit 106 checks the exhaust temperature ‘GAMMA’ ºC with the first and second pre-defined temperature values. For example, the control unit 106 checks the if the exhaust temperature ‘GAMMA’ ºC is between pre-defined temperature values X and Y, then the control unit 106 selects load A%

associated with the combination of the X and Y as the operating load point. If the exhaust gas temperature ‘GAMMA’ ºC does not exist between the X and Y, the control unit 106 checks whether the exhaust gas temperature is between pre-defined temperature values X1 and Y1. If the exhaust gas temperature is between the X1 and Y1, then the control unit 106 selects load B% associated with the combination of X1 and Y1. Otherwise, the control unit 106 checks whether the exhaust gas temperature ‘GAMMA’ ºC is between pre-defined temperature values X2 and Y2. On determining that the exhaust gas temperature ‘GAMMA’ ºC is between X2 and Y2, the control unit 106 selects load C% as the operating load point. Otherwise, the control unit 106 checks whether the exhaust gas temperature ‘GAMMA’ ºC is between pre-defined temperature values X3 and Y3. On determining that the exhaust gas temperature ‘GAMMA’ ºC is between X3 and Y3, the control unit 106 selects load D% as the operating load point. Otherwise, the control unit 106 checks whether the exhaust gas temperature ‘GAMMA’ ºC is between pre-defined temperature values X4 and Y4. On determining that the exhaust gas temperature ‘GAMMA’ ºC is between X4 and Y4, the control unit 106 selects load E% as the operating load point. Thus, the operating load point can be at least one of E%, D%, C%, B% and A%.
[0032] Further, the control unit 106 compares the exhaust gas temperature ‘GAMMA’ ºC with the ideal temperature in the look up table. The ideal temperature may be ‘DELTA’ ºC. The ideal temperature can be the exhaust gas temperature observed during the required flow of the gaseous fuel at the operating load point E% (or it can be D%/ C%/B%/A%) and the operating engine speed ‘ALPHA’ rpm.
[0033] In an embodiment, the control unit 106 maintains the same flow of the gaseous fuel to the fuel injector 208 of the dual-fuel engine 202 on determining that the exhaust gas temperature ‘GAMMA’ ºC is equal to the ideal temperature ‘DELTA’ ºC (which indicates the correct gaseous fuel flow (‘BETA’ kg/h)). In another embodiment, the control unit 106 increases the flow of the gaseous fuel to the fuel injector 208 of the dual-fuel engine 202 on determining that the exhaust gas temperature ‘GAMMA’ ºC is lower the ideal temperature

‘DELTA’ ºC (which indicates that the current gaseous fuel flow (‘BETA’ kg/h) is low). In yet other embodiment, the control unit 106 reduces the flow of the gaseous fuel to the fuel injector 208 of the dual-fuel engine 202 on determining that the exhaust gas temperature ‘GAMMA’ ºC is higher than the ideal temperature ‘DELTA’ ºC (which indicates the current gaseous fuel flow (‘BETA’ kg/h) is high). Thus, exhaust gas temperature parameter can be used to calculate the operate load point and accordingly for controlling the fuel flow to the dual-fuel engine 202.
[0034] Embodiments herein consider the exhaust gas temperature as a reference to adjust the gaseous fuel flow for different rpms and load points. When the gaseous fuel flow and the operating load increases, the exhaust temperature can drops and falls in a defined zone. Thus, embodiments herein use the exhaust gas temperature to determine the operating load point. in a speed governed diesel engine operating in at least one of a dual fuel mode and a mono fuel mode.
[0035] Embodiments herein use the exhaust temperature to control the gaseous fuel flow more accurately according to the calculated load and the rpm (engine operating speed). Thus, improving fuel substitution rate, overall fuel economy and reducing emissions.
[0036] Embodiments herein ensure no wastage of the gaseous fuel and maximum total fuel efficiency (the liquid fuel and the gaseous fuel). Embodiments herein achieve maximum fuel substitution by reducing the excess gaseous fuel flow which further reduces emissions.
[0037] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in FIG. 1 and FIG. 2 can be at least one of a hardware device, or a combination of hardware device and software module.
[0038] The embodiments herein disclose methods and systems for controlling a fuel flow in a vehicle with a dual-fuel engine. Therefore, it is understood that the scope of the protection is extended to such a program and in addition to a computer readable means having a message therein, such computer

readable storage means contain program code means for implementation of one or more steps of the method, when the program runs on a server or mobile device or any suitable programmable device. The method is implemented in at least one embodiment through or together with a software program written in e.g. Very high speed integrated circuit Hardware Description Language (VHDL) another programming language, or implemented by one or more VHDL or several software modules being executed on at least one hardware device. The hardware device can be any kind of portable device that can be programmed. The device may also include means which could be e.g. hardware means like e.g. an ASIC, or a combination of hardware and software means, e.g. an ASIC and an FPGA, or at least one microprocessor and at least one memory with software modules located therein. The method embodiments described herein could be implemented partly in hardware and partly in software. Alternatively, the invention may be implemented on different hardware devices, e.g. using a plurality of CPUs.
[0039] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of embodiments and examples, those skilled in the art will recognize that the embodiments and examples disclosed herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

We claim:
1. A control system (102) for controlling fuel flow in a vehicle (100) with a dual-
fuel engine (202), the control system (102) comprising:
a measuring module (104) associated with the dual-fuel engine (202) configured to:
measure at least one operating parameter of the dual-fuel engine (202), wherein the at least one operating parameter includes engine operating speed and an exhaust gas temperature; and a control unit (106) coupled to the measuring module (104) configured to:
calculate at least one operating load point based on the measured exhaust gas temperature; and
control flow of gaseous fuel to the dual-fuel engine (202) according to the at least one calculated operating load point and the engine operating speed.
2. The control system (102) of claim 1, wherein the measuring module (104) includes at least one sensor to determine the at least one operating parameter of the dual-fuel engine and the exhaust gas temperature.
3. The control system (102) of claim 1, wherein the control unit (106) is further configured to:
check if the measured exhaust gas temperature is between at least one first pre-defined value and at least one second pre-defined value; and
select at least one load point associated with a combination of the at least one first pre-defined value and the at least one second pre-defined value as the at least one operating load point in response to determining that the exhaust gas temperature is between the at least one first pre-defined value and the at least one second pre-defined value.

4. The control system (102) of claim 1, wherein the control unit (106) is further
configured to:
compare the exhaust gas temperature with at least one ideal temperature stored in a look-up table;
calculate a temperature difference between the exhaust gas temperature and the at least one ideal temperature; and
control the flow of the gaseous fuel to the dual-fuel engine for the calculated at least one operating load point and the engine operating speed based on the calculated temperature difference.
5. The control system (102) of claim 4, wherein the at least one ideal temperature is exhaust gas temperature observed during required flow of the gaseous fuel for the calculated at least one operating load point and the at least one operating speed.
6. The control system (102) of claim 4, wherein the control unit (106) is further configured to:
increase the flow of the gaseous fuel in response to determining the temperature difference with respect to look up table value is positive;
decrease the flow of the gaseous fuel in response to determining the temperature difference with respect to look up table value is negative; and
maintain the same flow of the gaseous fuel in response to determining the temperature difference with respect to look up table value is zero.
7. A method for controlling fuel flow in a vehicle (100) with a dual-fuel engine
(202), the method comprising:
determining, by a measuring module (104), at least one operating parameter of the dual-fuel engine, wherein the at least one operating parameter includes engine operating speed;
determining, by the measuring module (104), exhaust gas temperature of the dual-fuel engine (202); and

calculating, by a control unit (106), at least one operating load point based on the determined exhaust gas temperature.
8. The method of claim 7, further comprising controlling, by the control unit (106), the flow of gaseous fuel to the dual-fuel engine 202 according to at least one calculated operating load point and the engine operating speed.
9. The method of claim 7, wherein the measuring module (104) includes at least one sensor to determine the at least one operating parameter of the dual-fuel engine and the exhaust gas temperature.
10. The method of claim 7, wherein calculating the at least one operating load
point includes
checking if the measured exhaust gas temperature is between at least one first pre-defined value and at least one second pre-defined value; and
selecting at least one load point associated with a combination of the at least one first pre-defined value and the at least one second pre-defined value as the at least one operating load point in response to determining that the exhaust gas temperature is between the at least one first pre-defined value and the at least one second pre-defined value.
11. The method of claim 8, wherein controlling the flow of the gaseous fuel to the
dual-fuel engine (202) includes
comparing the exhaust gas temperature with at least one ideal temperature stored in a look-up table;
calculating a temperature difference between the exhaust gas temperature and the at least one ideal temperature; and
controlling the flow of the gaseous fuel to the dual-fuel engine (202) for the calculated at least one operating load point and the engine operating speed based on the calculated temperature difference.

12. The method of claim 11, wherein the at least one ideal temperature is exhaust gas temperature observed during required flow of the gaseous fuel for the calculated at least one operating load point and the at least one operating speed.
13. The method of claim 11, further comprising:
increasing the flow of the gaseous fuel in response to determining the temperature difference is positive;
decreasing the flow of the gaseous fuel in response to determining the temperature difference is negative; and
maintaining the same flow of the gaseous fuel in response to determining the temperature difference is zero.