Diesel fuel injection system
The fuel injection system is a vital part of the diesel engine. This system pressurizes and injects the fuel. In this way the fuel is forced into air, which has been compressed to high pressure in the combustion chamber.

The diesel fuel injection system consists of a fuel injection pump, an injection nozzle, a feed pump, a fuel filter and a high-pressure pipe. The fuel injection pump pressurizes fuel to high pressure and then sends it via the high-pressure pipe to the injection nozzle, which injects the fuel into the cylinder. The feed pump sucks the fuel from the fuel tank and the fuel filter of course filtrates the fuel. Some types of fuel tanks have a fuel sedimentor at the bottom of the filter to separate water content from the fuel.

Functions of the system
The fuel injection system has four functions: feeding the fuel, adjusting the fuel quantity, adjusting  injection timing and atomising the fuel.

Feeding fuel
Pump elements such as the cylinder and the plunger are built into the injection pump body. The fuel is compressed to high pressure when the cam lifts the plunger. Then it is sent to the injector.

Adjusting fuel quantity
Adjusting the fuel quantity is performed by a combination of the pump's adjusting mechanism and governor.

With diesel engines the intake of air is almost constant, irrespective of the rotating speed and load. If the injection quantity is changed with the engine speed and the injection timing is constant, the output and the fuel consumption changes. Since the engine output is almost proportional to the injection quantity, this is adjusted according to the opening degree of the accelerator pedal.

Adjusting injection timing
A certain period of time is required between the point when the fuel is injected, ignited and combusted and the point when the maximum combustion pressure is reached. This is due to ignition delay.

This period of time is almost constant, irrespective of the engine speed. Therefore a timer is used to adjust and change injection timing. In this way the optimum combustion is obtained to the change in engine speed.

Atomising fuel
Fuel is pressurised by the injection pump and then atomised from the injection nozzle. Accordingly, the fuel thoroughly mixes with air, thus improving ignition. The result is complete combustion. The injection nozzle is secured by the nozzle holder and is mounted on each cylinder of the engine.