All diesel engines draw air only, past the intake valve into the cylinder. A high-pressure fuel-injection system injects fuel into the cylinder. The amount of fuel injected is varied to suit the load on the engine, and to control engine speed. Intake air volume does not change.
In a basic diesel fuel system, a fuel tank holds the diesel fuel. A lift pump takes fuel from the tank. It keeps the injection pump full of fuel. A sedimenter removes any water, and larger particles in the fuel. A fuel filter removes minute particles. An injection pump delivers fuel under very high pressure to the injectors, along injector pipes. It must send the correct amount of fuel, and it must send it at the correct time in the engine cycle. An injector, at each cylinder, sprays fuel into each combustion chamber. Leak-off pipes take fuel used for cooling, and for lubrication, from the injection pump and injectors back to the tank. They also help to remove air from the system. A governor controls engine speed. And a control lever on the governor is connected to the accelerator pedal.
The basic system is divided into two sections. This is the low-pressure side.
The low-pressure side cleans the fuel and delivers it to the high-pressure side, or fuel injection system. Dirt and water will damage a diesel fuel injection system. The highly polished components need a very efficient filtration system to ensure all traces of dirt and water are removed.
The highly-polished finish is achieved by lapping two components together to form a matched set. Matched components must not be interchanged after lapping is completed.
The high-pressure side of fuel injection system must raise the pressure of the fuel high enough to open an injector. This allows the fuel to be forced into the combustion chamber at the correct time.
