Field of the invention

This invention relates to a fuel injection system for a dual fuel engine and a method of operating a fuel injection system.

Background of the invention

Various types of fuel injection systems are known in the state of the art. Fuel injection systems comprise at least the following basic components namely a fuel tank, a pump, a fuel flow line and injectors. However, depending on the type of fuel to be used the fuel injection system varies in terms of the components they use. This is mainly due to the type of characteristics of the fuel. In case of gasoline engines the gasoline is first mixed with air and then injected into the cylinders of the engine. For this purpose fuel injection systems for gasoline engine comprise amongst other components a fuel pump which pressurizes the gasoline and supplies the gasoline to the injectors and the injector inject the gasoline in the manifold where it is mixed with air before entering the cylinder. However, newer fuel injection system of gasoline engines also comprise a common rail system where fuel is pumped into the common rail using the pump and the gasoline is pressurized in the rail and then directly injected into the cylinder. In case of diesel engines, the diesel is directly injected into the cylinder of the engine. In earlier diesel fuel injection system a specialized high pressure pump was used to pressurize the fuel to a higher valve and then inject the same into the cylinder. However, later system use a common rail system where fuel is pumped to the common rail using a pump, the pressurized fuel from the rail is then directly injected into the cylinder of the engine.

Fuel injection systems have to ensure that high pressure fuel is supplied to the engine. While supplying the high pressure fuel care has also to be taken that the components of the fuel injection system are able to withstand the pressure of the fuel. For this purpose fuel injection systems also have various type of pressure relief system which ensures that the pressure of the fuel does not exceed beyond a limit which can damage the fuel injection system.

Fuel injection systems employ different techniques for creating the required high pressure fuel to be supplied to the cylinder of the engine. One such technique is disclosed in the US patent number 7448361. Disclosed therein is a method of operating a fuel system during start up of a gasoline direct injection engine. The method discloses manner in which a pressure wave is generated in the fuel flow such that high pressure fuel can be injected into the cylinders of the internal combustion engine.

Brief description of the accompanying drawings

Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

Figure 1 illustrates a first embodiment of the fuel injection system in accordance with this invention; and

Figure 2 illustrates another embodiment of the fuel injection system in accordance with this invention

Detailed description of the invention

Figure 1 illustrates a fuel injection system 10 for a dual fuel engine comprising a fuel tank 12, pluralities of injectors 14 and a fuel flow path 16 fluidly connecting the fuel tank 12 and the pluralities of injectors 14. The fuel injection system is characterized by comprising a low pressure feed pump 18 located in the fuel flow path. At least one flow valve 20 is located in the fuel flow path 16 downstream of the low pressure feed pump 18 between the low pressure feed pump 18 and the pluralities of injectors 14. A check valve 22 located upstream of at least one flow valve 20 in between the low pressure feed pump 18 and at least one flow valve 20 and a control unit 24 is adapted to control operation of said at least one flow valve.

The pluralities of injectors 14 are mechanical injectors. The fuel flow path 16 enables the fuel to flow from the fuel tank 12 to the flow valve 20 and then to the pluralities of injectors 14. The flow valve 20 is a valve that can be operated between a first operative open position and a second operative closed position in a manner such that the flow of fuel in the second flow path 20 can be regulated. The check valve 22 allows flow of fuel only in one direction which is downstream of the flow valve in direction of the injectors. The fuel injection system also comprises an overflow fuel flow path 26.

For the purposes of this invention the dual fuel engine is an engine which utilizes diesel and CNG. The working of the dual fuel engine in accordance with this invention can be explained as follows. Persons skilled in the art will already be aware that an engine utilizing diesel fuel works on a compression ignition principle and an engine utilizing CNG works on a spark ignition principle. The dual fuel engine in accordance with this invention is adapted to use diesel and CNG in a manner such that diesel is used at least for pilot injection into the cylinder of the dual fuel engine and CNG is used for the main injection.

The method of operating the first embodiment of the fuel injection system 10 in accordance with this invention can be explained as follows. During the normal working mode of the engine the diesel fuel is used for the purposes of pilot injection while the CNG fuel is used for the purpose of the main injection. The fuel from is taken from the fuel tank 12 using a low pressure feed pump 18 and sent to at least one of the flow valve 20 located in the fuel flow path 16. The control unit 24 generates a signal for starting pilot fuel injection. The control unit 24 then actuates at least one of the flow valves 20 which are connected to at least one of the pluralities of injectors 14. The control unit 24 actuates at least one of the flow valves 20 the operation of the valve is changed from an operative open position to an operative closed position. The closing of the flow valve 20 generates a pressure pulse in fuel flow that flow downstream of the flow valve 20. The pressure pulse generated due to closing of the flow valve 20 is inversely proportional to the time taken to close the flow valve 20. The pressure pulse generated is also directly proportional to the supply pressure of the lower pressure fuel feed pump 18. Further when the flow valve 20 is actuated to operate in a operative closed position, the check valve 22 ensures that pressure oscillations are not sent back to the low pressure feed pump 18. After the pilot injection is completed the control unit 24 actuates the flow valve 20 in a manner such that the flow valve 20 operation changes from an operative closed position to an operative open position. When the flow valve 20 operates in an operative open position there the pressure in the fuel flow path 16 downstream of the flow valve 20 is reduced.

Figure 2 illustrates a second embodiment of the fuel injection system 10 for a dual fuel engine. The fuel injection system 10 comprises a fuel tank 12, a fuel rail 26, pluralities of injectors 14, a first fuel flow path 28 and at least one second fuel flow path 30. The fuel injection system 10 is characterized by a low pressure feed pump 18 located in first fuel flow path 28 fluidly connecting the fuel tank 12 and fuel rail 26. At least one flow valve 20 is located in at least one second fuel flow path 30 fluidly connecting the fuel rail 16 to the pluralities of injectors 14. A check valve 22 is located upstream of the at least one flow valve 20 between the fuel rail 26 and the at least one flow valve 20 and a control unit 24 adapted to control operation of at least one flow valve 20 located in at least one second fuel flow path 30.

The fuel rail 26 in accordance with this invention is a fuel rail 26 which does not need to have any pressure regulating mechanism. The pluralities of injectors 14 are mechanical injectors. The first fuel flow path 28 and second fuel flow path 30 enable the fuel to flow from the fuel tank 12 to the fuel rail 26 and then to the pluralities of injectors 14. The flow valve 20 is a valve that can be operated between a first operative open position and a second operative closed position in a manner such that the flow of fuel in the second flow path 30 can be regulated. The check valve 22 allows flow of fuel only in one direction which is downstream of the fuel rail 26 in direction of the flow valve. The fuel injection system also comprises a third fuel flow path 32 which fluidly connects the flow valve 24 and the fuel tank 12. The third fuel flow path 32 is an overflow fuel flow path.

The method of operating the fuel injection system in accordance with this invention can be explained as follows. During the normal working mode of the engine the diesel fuel is used for the purposes of pilot injection while the CNG fuel is used for the purpose of the main injection. The fuel from is taken from the fuel tank 12 using a low pressure feed pump 18 and sent to the fuel rail 26 via the first fuel flow path 28. The control unit 24 generates a signal for starting pilot fuel injection. The control unit 24 then actuates at least one of the flow valves 20 which is connected to an injector 14. The control unit 24 actuates at least one of the flow valves 20 the operation of the valve is changed from an operative open position to an operative closed position. The closing of the flow valve 20 generates a pressure pulse in fuel flow that flow downstream of the flow valve 20. The pressure pulse generated due to closing of the flow valve 20 is inversely proportional to the time taken to close the flow valve 20. The pressure pulse generated is also directly proportional to the supply pressure of the lower pressure fuel feed pump. Further when the flow valve 20 is actuated to operate in an operative closed position, the check valve 22 ensures that pressure oscillations do not enter the fuel rail 26. After the pilot injection is completed the control unit 24 actuates the flow valve 20 in a manner such that the flow valve operation changes from an operative closed position to an operative open position. When the flow valve 20 operates in an operative open position there the pressure in the second fuel flow path 30 is reduced.

The fuel injection system and the method of operating the fuel injection system in the manner explained above can be done for each of the cylinder of the dual fuel engine during the engine work cycle. It must be understood that the explanation given above regarding the fuel injection system is only illustrative and does not limit the scope of this invention. The scope of this invention is only limited by the scope of the claim. Many modifications to the embodiments with regard to the type of valve used as check valve, flow valve, size of the fuel flow paths are envisaged and are within the scope of this invention.

We Claim:

1. A fuel injection system (10) for a dual fuel engine comprising a fuel tank (12), pluralities of injectors (14), a fuel flow path (16) fluidly connecting said fuel tank (12) to said pluralities of injectors (14),

Characterized in that said fuel injection system (10) comprising

- a low pressure feed pump (18) located in said fuel flow path (16);

- at least one flow valve (20) located in said fuel flow path downstream of said low pressure feed pump (18) between said low pressure feed pump (18) and said pluralities of injectors (14);

- a check valve (22) located upstream of said at least one flow valve (20) in between said low pressure feed pump (18) and said at least one flow valve (20);

- a control unit (24) adapted to control operation of said at least one flow valve.

2. A fuel injection system (10) as claimed in claim 1, wherein said control unit (24) controls operation of said at least one flow valve (20) in a manner such that said at least one flow valve (20) operates between a first operative open position and a second operative closed position.

3. A fuel injection system (10) as claimed in claim 1, wherein an overflow fuel flow path (26) fluidly connects said flow valve (20) and said fuel tank (12).

4. A fuel injection system (10) for a dual fuel engine comprising a fuel tank (12), a fuel rail (26), pluralities of injectors (14), a first fuel flow path (28) and at least one second fuel flow path (30), characterized in that

- a low pressure feed pump (18) located in said first fuel flow path (28) fluidly connecting said fuel tank (12) and said fuel rail (26);

- at least one flow valve (20) located in said at least one second fuel flow path (30) fluidly connecting said fuel rail (26) to said pluralities of injectors (14);

- a check valve (22) located upstream of said at least one flow valve (20) between said fuel rail (26) and said at least one flow valve (20);

- a control unit (24) adapted to control operation of said at least one flow valve (20) located in said at least one second fuel flow path (30).

5. A fuel injection system (10) as claimed in claim 4, wherein said control unit (20) controls operation of said at least one flow valve (20) in a manner such that said at least one flow valve (20) operates between a first operative open position and a second operative closed position.

6. A fuel injection system as claimed in claim 1, wherein said fuel injection system is for a dual fuel engine utilizing diesel and CNG.

7. A fuel injection system as claimed in claim 1, wherein said injection system comprises a third fuel flow path (32) establishing a fluid connection between said flow valve (24) and said fuel tank (12).

8. A method of operating a fuel injection system for a dual fuel engine, said method allowing at least one pilot fuel injection and at least one main fuel injection in at least one cylinder of said dual fuel engine, said method comprising the following steps:

- generating a fuel flow from a low pressure feed pump (18) towards a at least one flow valve (20);

- receiving signal from a control unit (24) for pilot fuel injection; and

- actuating at least one flow valve (20) in a manner such that said operation of said flow valve (20) is changed from an operative open position to an operative closed position;

- supplying fuel to at least one of pluralities of injectors (14) in dependence of actuating of said at least one flow valve (20);

- v receiving signal from a control unit (24) for stopping pilot fuel injection;

- actuating at least one flow valve (20) in a manner such that said operating of said at least one flow valve (20) is changed from an operative closed position to an operative open position.

9. A method as claimed in claim 5, wherein actuation of said at least one flow valve (20) from a operative open position to an operative closed position creates a pressure wave in said fuel flow downstream of said at least one flow valve (20) between said at least one flow valve (20) and at least one of said pluralities of injectors (14).