Fuel System

FUEL SYSTEM

The fuel system includes the following:
- low pressure fuel system that delivers the fuel from the fuel tank to the high pressure pump
- high pressure fuel system that increases the fuel pressure and delivers it to the fuel injectors
- fuel cooler system that cools the fuel returning from the injectors and the high pressure fuel injection pump

Fuel System (Part 1):

Fuel System (Part 2):

Low Pressure Fuel System
Fuel is pumped from the fuel tank to the primary fuel filter by the electric fuel pump (both located in the fuel conditioning module). Pressurized and filtered, approximately 34.5-69 kPa (5-10 psi) during engine idle, the fuel is pumped through the fuel supply line to the secondary fuel filter (the secondary fuel filter housing is located on the front left side of the engine). The filtered fuel leaves the secondary fuel filter and flows to the high pressure pump. The pressure regulator (located in the secondary fuel filter) relieves the pressure, sending some of the fuel back through the fuel return line to the fuel conditioning module and to the fuel tank.

Low Pressure Fuel System:

High Pressure Fuel System
After the filtered fuel leaves the secondary fuel filter it flows to the high pressure fuel injection pump. The high pressure fuel injection pump is gear driven by the camshaft gear and is located at the rear of the engine. Refer to the Engine Control Components High Pressure Fuel Injection Pump for fuel pump operation. The high pressure fuel injection pump increases the fuel pressure up to 169.96 MPa (24,650 psi) and delivers fuel to the fuel rails through 2 high pressure lines, 1 per bank. The system pressure generated by the high pressure fuel injection pump is constantly adjusted by the powertrain control module (PCM) for every operational condition. However, due to the storage volume of the fuel rails, the injection pressure remains constant over the duration of the injection process. Each fuel rail is connected to 4 injectors through individual high pressure pipes. The injectors are controlled by.the PCM and are capable of delivering exact fuel quantity based on the operational demands. The fuel injectors are operated in 3 stages: fill stage, main injection stage and end of main injection stage. The fill stage reduces the combustion noise, mechanical load and exhaust emissions. Refer to the Fuel System Fuel Injector Operation on fuel injector operation. The high pressure pump also delivers fuel to the fuel cooler. Refer to Engine Control Components Fuel Cooler. Engine Control Components

High Pressure Fuel System:

Fuel Injector Operation
The fuel injectors operate in 3 stages:
- fill stage
- main injection stage
- end of main injection stage

Fill Stage
During the fill stage the high pressure fuel enters the control piston chamber, spring side of the fuel injector valve and the high pressure chamber. The piezo actuator is not energized during this stage. The control piston and the needle control spring downward force overcomes the upward force in the high pressure chamber. Therefore, the nozzle needle is seated and no fuel can enter the combustion chamber.

Main Injection Stage
When the PCM commands the fuel injector on, the piezo actuator is energized and pushes the valve piston downward. The downward force of the valve piston pushes the fuel injector valve and fuel injector valve return spring down which opens up a bore hole that connects the control piston chamber with the fuel return chamber. When this happens a small amount of fuel flows from the control piston chamber to the fuel return chamber reducing the pressure and the downward force of the control piston. The pressure drop is enough for the upward force in the high pressure chamber to overcome the downward force of the control piston which allows the nozzle needle to move up, the fuel to atomize and enter the combustion chamber.

End of Main Injection Stage
The small amount of fuel that flows from the control piston chamber to the fuel return chamber during the main injection stage is routed down a drilled passage to the drain holes. The drain holes are located in the sides of the injector, below the O-ring. The fuel then returns to the fuel supply system through the passages in the cylinder head. When the desired injection timing is reached the PCM de-energizes the piezo actuator which causes the valve piston to move upward, and the fuel injector valve return spring to push the fuel injector valve up and seal the bored passage between the control valve chamber and the fuel return chamber, not allowing any fuel through. The pressure in the control valve chamber increases, causing the downward force of the control piston to overcome the upward force in the high pressure chamber, seating the nozzle needle and preventing the fuel from entering the combustion chamber.

Fuel Cooling System
The fuel cooling system is required to maintain an acceptable fuel and turbocharger actuator temperature during the engine operation. The fuel system temperature is monitored by the fuel rail temperature (FRT) sensor, which is an input to the PCM. The PCM commands the fuel cooler pump on by grounding the pump when the fuel or turbocharger actuator temperature exceeds the calibrated threshold. The coolant in the system flows from the fuel to. coolant heat exchanger to the fuel cooler reservoir, to the turbocharger actuator, to the fuel cooler air to coolant heat exchanger, to the fuel cooler pump and back to the fuel to coolant heat exchanger.

Fuel Cooling System:

Fuel Pump System

Fuel Pump Operation
After the low pressure fuel is filtered by the secondary fuel filter, it enters the high pressure fuel injection pump. When the fuel reaches the high pressure pump, its pressure is stepped up by the transfer pump. The transfer pump is internal to the high pressure fuel injection pump and is driven by the high pressure fuel injection pump main shaft. A portion of the fuel leaving the transfer pump flows to the lubrication valve which allows the fuel to lubricate the mechanical components of the high pressure injection fuel pump. Fuel that is not used for pump lubrication is directed to the fuel volume control valve. The fuel volume control valve regulates how much fuel enters the inlet one way check valve and the 3 main pump pistons. Refer to the Engine Control Components, Fuel Volume Control Valve. The 3 main pump pistons are actuated by the main shaft offset journal. The offset journal of the main shaft uses a free-spinning hub to make contact with the 3 main pump pistons. The pistons start their compression stroke when actuated by the offset journal and are returned to their rest position by the spring pressure. The fuel is drawn into the main cylinder while the piston returns to the rest position. The outlet check valve ball remains closed while the fuel is drawn in due to suction. Once the piston starts its compression stroke, the inlet one-way check valve closes using spring and fuel pressure and the outlet check valve opens due to increasing fuel pressure. After the high pressure fuel leaves the 3 main pump pistons its pressure is controlled by the fuel pressure control valve. The fuel pressure control valve adjusts the fuel pressure by restricting the fuel flow to the return line. Refer to the Engine Control Components, Fuel Pressure Control Valve. A portion of the fuel leaves the high pressure fuel injection pump and flows to the fuel cooler and the rest of the fuel is delivered to the high pressure fuel rails and injectors. Engine Control Components

During certain driving conditions the PCM cycles the fuel pump on and off for testing purposes and is considered normal operation.

High Pressure Fuel Injection Pump Operation:

Cetane Number
The cetane number relates to the auto-ignition quality of diesel fuel. The rating applies to diesel fuel similar to octane rating for gasoline. A measure of how readily diesel fuel starts to burn (auto ignites) at a high compression temperature. Diesel fuel with a high cetane number auto-ignites shortly after injection into the combustion chamber. Therefore, it has a short ignition delay time. Diesel fuel with a low cetane number resists auto-ignition. Therefore, it has a longer ignition delay time. A minimum cetane of 40 is required for a optimal driveability and performance.