FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See Section 10; rule 13)
TITLE OF THE INVENTION
System and method for controlling liquid carryover in gaseous LPG
powered engines
APPLICANTS
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Mr. Muthu Shanmugam R, Mr. Viswanatha H.C,
Mr. Nilesh M Kankariaya and Mr. Srinivasan L
All Indian nationals of
TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed

FIELD OF INVENTION:
The present invention generally relates to Liquefied petroleum gas (LPG) fuelled vehicles and particularly to detect the presence of liquid carryover in LPG fuelled vehicles. More particularly the present invention relates to provide a system and method to control liquid carryover in gaseous LPG powered engines during cold engine operation.
BACKGROUND OF THE INVENTION:
An LPG powered vehicles includes a vaporizer to expand and modulate the fuel pressure as per engine's operational demands. The LPG is subjected to an expansion process in the vaporizer. In addition, the vaporizer regulates the downstream gas pressure to maintain the differential pressure across an injectors/mixer constant irrespective of the engine's operational demands.
In applications like LPG, in addition to expansion, there is a phase change occurring inside the vaporizer. As a result of the expansion and the phase change process, the temperature and pressure of the working fluid reduces. The rate of fuel vaporization is directly proportional to the temperature of the coolant in the vaporizer. The LPG fuelled engines are prone to liquid carryover during cold engine operation. The situation is aggravated during high fuel demand (high engine load) conditions as the required rate of vaporization is high. The term cold engine is used to define the working state of the engine when the engine coolant temperature is equal to that of the ambient. During cold engine operation, the heat energy of the coolant is insufficient to prevent freezing in the vaporizer. If high fuel demand is encountered during such operating conditions, the working fluid undergoes incomplete phase change. This results in a phenomenon known as "liquid carryover", wherein liquid LPG gets entrained in the low pressure gas circuit where the gaseous LPG is demanded.

The liquid carryover occurs when free liquid escapes with the gas phase and indicates high liquid level. The liquid carryover results in improper engine functioning leading to driveability and emission issues• This is mainly due to the uncontrolled expansion of the liquid LPG, which eventually leads to very high variations in the fuel pressure. As a result, the amount of fuel injected into the engine varies drastically leading to air-fuel ratio fluctuations. The Failure to precisely evaluate liquid carryover can eventually result in driveability and emission issues during cold engine operation especially low/lack of engine response to acceleration inputs. It results in high emissions due to fluctuations in density of the fuel injected which consequently varies the air-fuel ratio of the fuel-air mixture. It results in mechanical failure of fuel system polymer components due to stiffening (Joule Thomson effect) and mechanical failure of metallic fuel system
In conventional systems vehicle driveability is used as an indicative parameter to evaluate liquid carryover. During liquid carryover in cold engine operation, the vehicle suffers from lack of response to acceleration inputs due to extremely rich air-fuei ratio. The conventional evaluation technique lacks a quantitative approach to control liquid carryover. Moreover the driveability is a subjective parameter and varies drastically depending on the engine operating conditions (such as ambient conditions, coolant temperatures, engine speed, engine load, rate of acceleration etc) and in some cases it depends on the driving pattern. Furthermore, this method lacks consistency and is difficult to interpret the results of this evaluation technique. It is highly uncertain that the observations on one vehicle will match with the observations on the other. The conventional methods are generally applicable to fluid streams in large stationary pipelines conveying gases and involve installation of additional measuring / detecting apparatus. Consequently, the cost involved is also high. Furthermore, in automotive applications, the scope of installing additional measuring / detecting apparatus inside the vehicle or in the engine bay area is limited. The difficulty exists in interpreting the data to control the engine operation during liquid carryover condition.

OBJECTS OF THE INVENTION
The primary object of the present invention is to obviate the above mentioned drawbacks.
Another object of the present invention is to provide a system and method to control liquid LPG carryover during cold/warm engine operation.
Yet another object of the present invention is to provide a system and method to interpret the data from a plurality of sensors by an engine controller to control the operation of engine during liquid carryover in LPG fuelled vehicles.
Yet another object of the present invention is to minimize the liquid LPG carryover in gas LPG powered engines when it is experiencing high engine loads under cold engine condition.
SUMMARY OF THE INVENTION
The embodiments of the present invention provide a system and method for controlling liquid carryover in gaseous LPG powered mono fuel or bi-fuel engines. The system comprises an engine controller, a temperature sensor located in a low pressure fuel feed line connecting a vaporizer to said engine, an oxygen sensor located in the exhaust manifold of said engine, a throttle position sensor and a coolant temperature sensor connected to said engine. The system includes an engine controller to monitor output from said sensors. The engine controller compares the physical variables with their limits and based on the comparison, selectively operates said engine in normal operating mode or restricted operating mode. The data from the plurality of sensors are interpreted by the engine controller to control the engine operation. In an exemplary embodiment, said bi-fuel engines operate in gasoline and LPG fuels. In an exemplary embodiment an indication means is connected to the engine controller.

A method for controlling the liquid carryover in gaseous LPG powered mono-fuel or bi-fuel engines is provided. The method includes monitoring said system in LPG mode, an engine coolant temperature, an engine speed and an engine load. The method further includes measuring the output voltage of a temperature sensor and an oxygen sensor. Detecting the liquid carryover based on the LPG temperature and oxygen sensor voltage and selectively operating said engine in restricted operating mode or normal operating mode based on presence or absence of liquid carryover respectively. The presence of liquid LPG carryover is detected when the LPG temperature is less than or equal to a predefined threshold and the oxygen sensor voltage is greater than or equal to a predefined threshold. The coolant flow rate or transition temperature is increased when the liquid carryover is detected to prevent freezing of the working fluid in the vaporizer simultaneously the LPG temperature is gradually increased over a period of time until it reaches equilibrium.
According to exemplary embodiment, the method includes said controller to limit the engine operating speed by introducing a fuel cut-off to reduce the engine's fuel demand during said restricted operating mode. In another exemplary embodiment, the engine controller limits the opening of said throttle body irrespective of throttle demand by driver to avoid high load or high fuel demand during said restricted operating mode. In another exemplary embodiment, said engine controller prevents said bi-fuel engine from operating in LPG mode until said coolant temperature exceeds predetermined threshold/transition temperature in restricted operating mode and said controller activates an indicating means during said restricted operating mode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of the system for controlling liquid carryover in gaseous LPG powered engines, according to an exemplary embodiment of the present invention.

FIG. 2 shows a flow chart to illustrate the detection and the control measures to minimize the liquid carryover during engine operation in LPG mode, according to an exemplary embodiment of the present invention.
FIG. 3 shows a flow chart to illustrate the conditions essential to indicate the liquid LPG carryover and analysis of the data to conclude the presence of liquid in a gas stream, according to an exemplary embodiment of the present invention.
FIG. 4 shows a graph illustrating a gas temperature and air fuel ratio (Lambda) during liquid carryover, according to an exemplary embodiment of the present invention.
FIG. 5 shows a graph illustrating a gas temperature and air fuel ratio (Lambda) in the absence of liquid carryover,according to an exemplary embodient of the present invention.
DETAILED DESCRIPTION
Due to limitations as described above there is a need to provide a system and method to control liquid LPG carryover during cold/warm engine operation. The system and method according to present invention interprets the data from a plurality of sensors and an engine controller to control the engine operation during liquid LPG carryover.
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same.
The various embodiments of the present invention provide a system and method for controlling liquid carryover in gaseous LPG powered mono-fuel or bi-fuel engines. FIG. 1 shows a block diagram of the system for controlling liquid carryover in gaseous LPG powered engines, according to an exemplary embodiment of the present invention. The system comprises an engine controller 6, a vaporizer 1

connected to said engine 5 by means of a low pressure fuel feed line 3, a temperature sensor 4 provided in said feed line 3, a oxygen sensor 7 provided in an exhaust manifold of said engine 5, a throttle position sensor 11 and a coolant temperature sensor 12 connected to said engine 5. A line 2 feeds liquid LPG at high pressure to the vaporizer 1. The vaporizer 1 is heated by circulating a hot coolant from the engine 5 through circulation pipes 9 and 10. The liquid LPG undergoes expansion in the vaporizer 1 and is fed to the engine 5 as fuel through the low pressure fuel feed line 3. The temperature of the fuel is monitored by the temperature sensor 4 which relays the signal to the engine controller 6. The operation of the engine 5 is controlled by the engine controller 6. The engine controller 6 utilizes the feedback signal from the plurality of sensors to control the engine 5 operation and meet the driver's demand. The gaseous fuel after combustion in the combustion chamber of the engine 5 is exhaled through the exhaust manifold 7. The 02 sensor 8 fitted on the exhaust manifold senses the oxygen concentration in the exhaust gas stream and relays the information of the engine's operating air-fuel ratio to the engine controller 6. In an exemplary embodiment, the bi-fuel engines operate in gasoline and LPG fuels. In another exemplary embodiment, an indication means 13 is connected to the engine controller.
During cold engine operating conditions, the temperature of the gaseous LPG in feed line 3 drops drastically due to phase change and lack of sufficient heat energy from the circulating coolant 9. If the operating demand conditions are held constant, the temperature of LPG in the feed line 3 drops till it reaches the boiling point of LPG. This temperature drop is captured by the temperature sensor 4 fitted on the low pressure fuel feed line 3. Due to incomplete phase change and uncontrolled expansion of liquid LPG in the low pressure LPG feed line 3, the density of working fluid in the low pressure fuel feed line 3 fluctuates. As a result, the fuel injected also varies. This consequently changes the air to fuel ratio. During liquid carryover conditions, the engine 5 operates under extremely rich air-fuel ratio which is indicated by lambda lower than 1 or 02 sensor voltage continuously

greater than 700mV. According to an exemplary embodiment of the present invention, the presence of liquid LPG carryover is detected by the engine controller when the LPG temperature is less than or equal to a predefined threshold and the oxygen sensor voltage is greater than or equal to a predefined threshold. The coolant flow rate or transition temperature is increased when the liquid carryover is detected to prevent freezing of the working fluid in the vaporizer simultaneously the LPG temperature is gradually increased over a period of time until it reaches equilibrium. By analyzing the exhaust gas 02 content using the 02 sensor 8, inference on the air-fuel ratio can be judged. As a plausibility check, the controller uses the information from the throttle position sensor 11 and coolant temperature sensor 12 to verify the engine operating load and temperature. The controller 6 then compares the value of these four variables to their respective threshold limits to detect the presence of liquid carryover. In the likely event of liquid carryover, the controller 6 operates the engine 5 in restricted operating mode. In the absence of liquid carryover, the controller 6 operates the engine 5 in normal operating mode.
In normal operating mode, the engine controller 6 operates the engine 5 without any restrictions and indications. In an exemplary embodiment in restricted operating mode in case of general engines, the engine controller 6 limits the engine 5 operating speed by introducing a fuel cut-off to reduce the engine's fuel demand. This is followed by an indication to the driver, typically through the driver information display 13. In another exemplary embodiment in restricted operating mode in case of engines equipped with throttle body, the engine controller 6 limits the opening of the throttle body irrespective of the throttle demand by driver to avoid high load or high fuel demand and gives an indication to the driver, typically through the driver information display 13. In another exemplary embodiment in restricted operating mode in case of bi-fuel engines said engine controller 6 prevents the bi-fuel engine from operating in LPG mode until said coolant temperature exceeds predetermined threshold/transition temperature and said controller activates an indicating means to the driver.

The FIG. 1 serves as a basic model and that the countless variations of the system are well within the scope of the invention. Although the vaporizer 1 described is of diaphragm type, the present invention is also suited for piston and spring type vaporizers. The construction of the vaporizer 1 can either be single stage or multiple stages. The vaporizer 1 shown is heated by circulating the hot engine coolant. However the invention is also suited for electrical heated vaporizers and others types which require external heating. The temperature sensor 4 can be of NTC thermister type or basic thermocouples to measure the fluid temperature. The 02 sensor 8 can be of Nernst switching type, planar broadband sensors or indicating type heated exhaust gas oxygen (HEGO) sensors. Other types of transducers and devices can be used within the broad scope of the present invention to measure the temperature and the air-fuel ratio. The engine's fuel injection system can be of sequential /semi-sequential injection system or carburetor /air- valve type fuel feed system. Although the basic engine 5 described here pertains to bi-fuel LPG (operation in both gasoline and LPG), the invention is also suited for dedicated LPG engines.
FIG. 2 shows a flow chart to illustrate the detection and the control measures necessary to minimize the liquid carryover during engine operation in LPG mode, according to an exemplary embodiment of the present invention. The detection method includes to check the initializing conditions, measuring the temperature in feed line and oxygen sensor voltage, evaluating of LPG carryover condition and take possible preventive action to avoid carryover of liquid LPG. The initializing conditions include the controller to check if the engine is running in LPG (21), to check if the engine coolant temperature is less than threshold (22), to check if the engine speed is greater than threshold (23) and to check if the engine load is greater than the threshold (24). If the above conditions are not met then the control will wait till the initialization conditions are met (25). If the above conditions are met then the controller measures the LPG temperature in rail and measures the oxygen sensor voltage (26).

The information from the temperature sensor 4 and the 02 sensor 8 is primarily used by the engine controller 6 to judge the presence of liquid carryover. If the LPG temperature is less than or equal to threshold (5°C) for more than lOsec (27) and if the oxygen sensor voltage is greater than or equal to threshold (700mv) for more than 10s (28), then the controller detects the presence of liquid carry over (The time value provided is just arbitrary to avoid misdetections due to fluctuations in the data acquisition). If the above conditions are not met then the liquid carry over is not present (29). Once the liquid carry over condition is detected a control measures are initiated by the engine controller 6 to control the LPG liquid carryover (31).
In an exemplary embodiment of the present invention, the control measures necessary to minimize the liquid carryover during engine operation in LPG are to indicate the presence of liquid carryover by flashing the malfunction indicator lamp (MIL) or other possible drivers aid (audio signal) provided in dashboard. To electronically limit the engine speed by introducing an engine fuel cut-off until the coolant temperature exceeds the threshold. To limit the throttle opening irrespective of the throttle demand by driver to avoid high load operation until the coolant temperature exceeds the threshold. To void the operation of engine 5 in LPG mode until coolant temperature exceeds the threshold /transition temperature.
FIG. 3 shows a flow chart to illustrate the conditions essential for indicating the liquid LPG carryover and analysis of the data to conclude the presence of liquid in the gas stream, according to an exemplary embodiment of the present invention. The condition necessary to indicate the presence of LPG carryover includes initializing the coolant circulating circuit (32) and the transition temperature at which the LPG operation is permitted (33), before starting the test sequence. If the initializing conditions are met then measuring coolant temperature and comparing said coolant temperature with set transition temperature during cold engine condition to operate said engine in LPG mode, test run and data acquisition and analyzing said acquired data to detect the presence the liquid carryover. Initially the coolant circulation system layout and the transition temperature are decided. As the

liquid carry over phenomenon is dependent on the coolant flow rate and its temperature, the layout of the coolant circuit is finalized before start of the test sequence. This consequently dictates the coolant flow rate through the vaporizer. In case of electrically heated systems, the heater duty cycle is finalized before execution of test. In bi-fuel vehicles, transition to LPG (operation in gasoline before transfer to LPG) is usually avoided until the coolant temperature exceeds a threshold value to prevent liquid carry over. The transition temperature threshold at which the LPG operation is permitted is pre-calibrated before executing the test.
During cold start engine, the engine controller 6 controller measures the coolant temperature (35). The controller checks if the coolant temperature is equal to the transition temperature to authorize LPG mode (36). If the coolant temperature is not equal to the transition temperature then the engine controller 6 wait for the conditions to be met (37). Then the engine controller 6 checks if the engine is running in LPG mode or not (38). If the engine 5 is running in LPG mode, then the engine controller 6 runs the engine 5 at high loads at speeds close to peak torque engine speed (40) and measure the LPG temperature and oxygen sensor voltage (41). If the engine 5 is not running in LPG mode then the engine controller runs the engine 5 in LPG mode (39).
In an exemplary embodiment, the engine controller 6 detects the presence of liquid carryover (46) if the LPG temperature is less than or equal to 5°C (42) and the oxygen sensor voltage is greater than or equal to 700mV (43). If the liquid carryover is present the engine controller increases the coolant flow rate or increases the transition temperature to control the liquid carryover (47). When there is no liquid carryover condition the engine controller 6 freeze the coolant flow rate and transition temperature till optimum condition is attained (45). The limiting threshold conditions required to judge the presence of liquid LPG in the gas stream is based on the signals from the temperature sensor 4 and 02 sensor 8. If there is a liquid carryover during the first few minutes of operation, the LPG temperature drops to 0 ±●5°C (depending on the propane and butane concentration in LPG),

which is captured by the temperature sensor 4. As a result of this temperature drop, the density of working fluid in the low pressure gas line 3 fluctuates. This consequently alters the fuel injected and the air to fuel ratio of the combustible mixture entering the engine 5. As the engine 5 operates under rich air-fuel ratio during liquid carryover conditions, the 02 sensor 7 generates voltage in excess of 700mV.
The engine 5 is operated at high fuel demand conditions immediately after a cold start. This is achieved by operating the engine at full throttle conditions close to the engine's peak torque speed. In bi-fuel vehicles, if the transition criteria are not met, the engine is maintained in idling until the required threshold conditions are attained. On effective transition to LPG, the engine is operated at the conditions mentioned above. Under such operating conditions, the temperature of the gaseous LPG after the vaporizer drops drastically due to high rate of vaporization and due to lack of sufficient heat energy from the circulating coolant. As the coolant temperature progressively increases during continuous engine operation, there is sufficient heat available in the coolant circulation system to prevent freezing of the working fluid. As a result, the possibility of liquid carryover diminishes at high coolant temperatures and the LPG temperature gradually increases over a period of time until it reaches equilibrium. The system provided herein for detecting liquid LPG carryover is particularly useful in determining the effectiveness of the coolant circulating / heating system in preventing liquid carryover. By modulating the temperature and the flow rate of coolant through the vaporizer 1, the occurrence of ■ liquid carryover can be avoided. This system is also be used as a tool to evaluate the heat exchange surface area required for effective heat transfer inside the vaporizer.
In case of bi-fuel vehicles, the operation in LPG is avoided until the coolant temperature exceeds a predetermined threshold thereby reducing the fuel demand and the possibility of liquid carryover. Alternatively, the maximum LPG demand during cold engine operation can be restricted to avoid liquid carry over. The

system effectively detects the occurrence of liquid carryover during stoichiometric operation of the engines using the engine controller, hence does not require any additional instruments. FIG. 4 and FIG. 5 show a graph illustrating a gas temperature and air fuel ratio (Lambda) during presence and absence of liquid carryover respectively, according to the present invention.
ADVANTAGES OF THE INVENTION
• The system and method according to present invention provide a quantitative approach to evaluate the liquid carryover using sensor signal information, the method is repeatable as sensor signal information is used to judge liquid carryover.
• The engine operation conditions are maintained such that the results on one vehicle can be easily confirmed or verified on the other vehicles.
• The system and method uses sensor information to detect liquid carry over which is quantitative and reliable. Further, since the liquid LPG carryover detection criteria are based on quantitative thresholds the method is reliable, repetitive and can be used to compare the vehicle to vehicle variability.
• By implementing the system and method according to present invention, the potential damage normally incurred due to liquid carryover can be avoided and the cost impact of the same can be reduced.
• The system is cost effective as the system does not require installation of any additional measuring/detecting apparatus.
• The system and method can be easily implemented in the existing LPG powered vehicles by simply integrating an engine controller and additional sensors.

The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

We claim:
1. A system for controlling liquid carryover in gaseous LPG powered mono-fuel or
bi-fuel engines, comprising;
an engine controller;
a temperature sensor located in a low pressure fuel feed line for connecting a
vaporizer to said engine;
a oxygen sensor located in the exhaust manifold of said engine;
a throttle position sensor and a coolant temperature sensor connected to said
engine; said engine controller communicating with said sensors for detecting the
liquid carryover based on the inputs from said sensors and controlling said engine
in a restricted operating mode during the liquid carryover.
2. The system according to claim 1, wherein said bi-fuel engine working in
gasoline and LPG fuels.
3. The system according to claim 1, wherein an indication means connected to said controller.
4. A method for controlling liquid carryover in gaseous LPG powered mono-fuel or bi-fuel engines by a system as claimed in claim 1 comprising the steps of; Monitoring LPG mode, engine coolant temperature, engine speed and engine load by said controller;
measuring output voltage of a temperature sensor and an oxygen sensor; Detecting the liquid carryover based on the LPG temperature and oxygen sensor voltage; and
selectively operating said engine in restricted operating mode or normal operating mode based on presence or absence of liquid carryover respectively;
5. The method according to claim 4, wherein detecting the presence of liquid LPG
carryover when the LPG temperature is less than or equal to a predefined threshold
and the oxygen sensor voltage is greater than or equal to a predefined threshold.

6. The method according to claim 4, wherein increasing the coolant flow rate or transition temperature when the liquid carryover is detected to prevent freezing of the working fluid in vaporizer and increasing the LPG temperature gradually over a period of time until it reaches equilibrium.
7. The method according to claim 4, wherein said controller limiting the engine operating speed by introducing a fuel cut-off to reduce the engine's fuel demand during said restricted operating mode.
8. The method according to claim 4, wherein said controller limiting the opening of said throttle body irrespective of throttle demand by driver to avoid high load or high fuel demand during said restricted operating mode.
9. The method according to claim 4, wherein said controller preventing said bi-fuel engine from operating in LPG mode until said coolant temperature exceeds predetermined threshold/transition temperature in restricted operating mode.
10. The method according to claim 4, wherein said controller activates an
indicating means during said restricted operating mode.