Claims:We Claim:
1. A low pressure circuit (10) in a fuel injection system, said low pressure circuit (10) comprising:
a rail (12);
a low pressure pump (14) in flow communication upstream from said rail (12), said low pressure pump (14) adapted to supply pressurized fuel to said rail (12);
a hydrocarbon injector (16) in flow communication downstream from said rail (12), said rail (12) adapted to supply pressurized fuel to said hydrocarbon injector (16) to deliver pressurized fuel to an exhaust gas flow path (18) of the fuel injection system.

2. The low pressure circuit (10) in the fuel injection system in accordance with Claim 1 wherein said rail (12) is in flow communication upstream from a high pressure fuel pump (20), said high pressure fuel pump (20) adapted to supply pressurized fuel to an engine (22).

3. The low pressure circuit (10) in the fuel injection system in accordance with Claim 2 wherein said rail (12) is in flow communication with said high pressure fuel pump (20) via a fuel supply path (24).

4. The low pressure circuit (10) in the fuel injection system in accordance with Claim 1 further comprising an overflow valve (26) connected to said rail (12), said overflow valve (26) adapted to channel excess fuel from said rail (12) to a fuel tank (28) of said fuel injection system.

5. The low pressure circuit (10) in the fuel injection system in accordance with Claim 1 further comprising a control valve (30) in flow communication downstream from said low pressure pump (14) and upstream from said rail (12), said control valve (30) prevents backflow of fuel from said rail (12) to said low pressure pump (14).

6. The low pressure circuit (10) in the fuel injection system in accordance with Claim 1 wherein said hydrocarbon injector (16) is in flow communication with said rail (12) via a fuel supply path (32).

7. The low pressure circuit (10) in the fuel injection system in accordance with Claim 1 wherein said low pressure pump (14) is in flow communication with said rail (12) via a fuel supply path (36).
, Description:Field of the invention
[0001] This invention relates to a fuel injection system and more particularly to a low pressure circuit in the fuel injection system.

Background of the invention
[0002] US 2013199160 A describes an internal combustion engine. An after treatment system is coupled to the internal combustion engine to receive an exhaust gas stream. The after treatment system comprises one or more modules. Each module includes one or more emission reducing devices to reduce undesirable constituents in the exhaust gas stream from the internal combustion engine. The emission reducing devices comprise a diesel particulate filter, a diesel oxidation catalyst, a selective catalytic reduction catalyst, and a DEF injection device upstream of the selective catalytic reduction catalyst. A NOX sensor is positioned downstream of the selective catalytic reduction catalyst. A hydrocarbon injection device is provided for injection of hydrocarbons in the exhaust gas upstream of one or both of thermal enhancer and the DOC. The hydrocarbon injection device may be connected to a fuel source of an engine or to a source of hydrocarbons.

Brief description of the accompanying drawing
[0003] Figure 1 illustrates a schematic diagram of a low pressure circuit in a fuel injection system.

Detailed description of the invention
[0004] Figure 1 illustrates a low pressure circuit 10 in a fuel injection system. The low pressure circuit 10 comprises a rail 12 and a low pressure pump 14 in flow communication upstream from the rail 12, the low pressure pump 14 adapted to supply pressurized fuel to the rail 12. A hydrocarbon injector 16 is in flow communication downstream from the rail 12, the rail 12 adapted to supply pressurized fuel to the hydrocarbon injector 16 to deliver pressurized fuel to an exhaust gas flow path 18 of the fuel injection system.
[0005] The low pressure circuit 10 further comprises the rail 12 in flow communication upstream from the high pressure fuel pump 20. The high pressure fuel pump 20 is adapted to supply pressurized fuel to an engine 22. The high pressure fuel pump 20 is in flow communication with the rail 12 via a fuel supply path 24. An overflow valve 26 is connected to the rail 12, the overflow valve 26 adapted to channel excess fuel from the rail 12 to a fuel tank 28 of the fuel injection system. A control valve 30 is in flow communication downstream from the low pressure pump 14 and upstream from the rail 12, the control valve 30 prevents backflow of fuel from the rail 12 to the low pressure pump 14. The hydrocarbon injector 16 is in flow communication with the rail 12 via a fuel supply path 32. The low pressure pump 14 is in flow communication with the rail 12 via a fuel supply path 36.
[0006] The low pressure circuit 10 of the fuel injection system comprises a fuel tank 28. A low pressure pump 14 is in flow communication with the fuel tank 28 and receives fuel that is supplied from the fuel tank 28. A control valve 30 is in flow communication with the low pressure pump 14 and prevents backflow of fuel to the low pressure pump 14 from the rail 12. The rail 12 receives fuel from the control valve 30 via a fuel flow path 36. An overflow valve 26 is connected to the rail 12 and allows flow of excess fuel from the rail 12 back to the fuel tank 28. When the pressure of fuel in the rail 12 is above a threshold pressure, the excess pressurized fuel is delivered from the rail 12 to the fuel tank 28 via the overflow valve 26. In accordance with one embodiment, the low pressure pump 14 may be a gearbox of a supercharger. The gearbox of the supercharger delivers compressed fuel to the control valve 30.
[0007] The rail 12 is in flow communication with a high pressure fuel pump 20. The rail 12 supplies pressurized fuel that is delivered to it to the high pressure fuel pump 20 via a fuel flow path 24. The pressurized fuel that is supplied to the high pressure fuel pump 20 is delivered to a fuel injector of an engine 22. The products of combustion from the engine 22 is channeled to an exhaust gas flow path 18 and subsequently vented to the atmosphere.
[0008] A hydrocarbon injector 16 is in flow communication with the exhaust gas flow path 18 and injects fuel into the exhaust gas flow path 18. A fuel flow path 32 is in flow communication with the hydrocarbon injector 16 and the rail 12. Pressurized fuel is supplied from the rail 12 to the hydrocarbon injector 16, from where it is injected into the exhaust gas flow path 18.

[0009] An engine control unit 40 is in electronic communication with the hydrocarbon injector 16 via a control path. When it is required to inject fuel from the hydrocarbon injector 16 into the exhaust gas flow path 18, the engine control unit 40 transmits an electronic signal to the hydrocarbon injector 16, thereby regulating the quantity and time duration for which fuel is required to be injected into the exhaust gas flow path 18. The fuel that is injected by the hydrocarbon injector 16 into the exhaust gas flow path 18 reacts with the exhaust gas that is discharged from the engine 22 to produce exhaust gas at an elevated temperature. The exhaust gas at the elevated temperature is channeled to the NOX storage catalytic chamber 42 where it facilitates regeneration of the NOX storage catalytic chamber 42. Therein, the exhaust gas is channeled to the diesel particulate filter 44 for filtering the exhaust gas before venting the exhaust gas out of the fuel injection system.
[0010] A working of the low pressure circuit 10 in the fuel injection system is described as an example. Fuel is channeled from the fuel tank 28 to the low pressure pump 14. From the low pressure pump 14, the fuel is supplied to the rail 12. Pressurized fuel that is above a threshold pressure is channeled from the rail 12 to the fuel tank 28 via the overflow valve 26. After the excess pressure is relieved, the fuel from the rail 12 is delivered to the high pressure fuel pump 20 where the pressure of the fuel is further increased and delivered to the engine 22. In addition, the fuel from the rail 12 is supplied to the hydrocarbon injector 16 via the fuel flow path 32.
[0011] When the NOX storage catalyst is required to be regenerated, fuel is delivered from the hydrocarbon injector 16. When it is required to deliver fuel from the hydrocarbon injector 16, the engine control unit 40 transmits an electronic signal to the hydrocarbon injector 16. The electronic signal is a function of the the time duration for which fuel is required to be injected by the hydrocarbon injector 16 into the exhaust gas flow path 18. Based on the electronic signal that is received, the hydrocarbon injector 16 opens for a specified time duration thereby allowing the required quantity of fuel to be injected into the exhaust gas flow path 18. The fuel that is injected by the hydrocarbon injector 16 inside the exhaust gas flow path 18 reacts with the exhaust gas flowing through the exhaust gas flow path 18, thereby generating products of combustion. These products of combustion are at an elevated temperature than the temperature of the exhaust gas flowing through the exhaust gas flow path 18. The elevated temperature of exhaust gas in the NOX storage catalytic chamber 42 that flows through the exhaust gas flow path 18 causes regeneration of the NOX storage catalyst. When it is required to stop the injection of fuel into the exhaust gas flow path 18 by the hydrocarbon injector 16 once the NOX storage catalyst is regenerated, the engine control unit 40 disconnects the electronic signal to the hydrocarbon injector 16, thereby stopping the injection of fuel inside the exhaust gas flow path 18.
[0012] The above mentioned process is extremely effective in regeneration of the NOX storage catalyst without the aid of an external heating means such as an electrical heater positioned within the NOX storage catalyst. It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to leverage and dimensions of various components are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.