Fuel System of Diesel Engine 1 of 2


The fuel system delivers the fuel to the engine. The injection pump is driven by the timing belt or the timing gear of engine.


The injection pump is driven by the camshaft in accordance with the engine. The fuel, which is highly compressed by the injection pump, is sent into the injection nozzle of each cylinder in order to be injected into the combustion chamber. Excess fuel is also returned to the fuel tank.

Diesel Engine Priming Pump

1. Description

The priming pump is a manual pump used for bleeding air when the fuel tank becomes empty, the fuel filter is replaced or the air is mixed into the fuel pipe. If air enters the fuel line, it may cause the injection pump to have difficulty in pumping the fuel up and the engine may be difficult to start. Therefore, it is necessary to bleed the air from the fuel system, using the priming pump before starting the engine. Also it is used when bleeding the water in the sedimenter.

2. Operation

(1) When pushing the pump handleWhen pushing the pump handle, the fuel or air inside the pump chamber opens the outlet check valve and flows to the fuel filter and injection pump. At the same time, the inlet check valve closes and reverse flow of fuel is prevented. The air that has entered into the injection pump flows with the fuel from the return pipe of the injection pump to the fuel tank.

(2) When releasing the pump handleWhen releasing the pump handle, the force of the spring pushes the diaphragm returning to its original position. At this time, a vacuum is created in the pump chamber. The inlet check valve opens and draws the fuel in with this vacuum. At the same time, the outlet check valve closes and reverse flow of fuel is prevented.

Diesel Engine Fuel Sedimenter

The fuel sedimenter separates the water from the diesel fuel. It uses the specific gravity difference between the diesel fuel and water to separate the water before the fuel enters the injection pump. The sliding portion inside the injection pump is lubricated by the fuel. Therefore it is necessary to drain the water from the fuel because lubrication is insufficient if fuel is mixed with water, as seizing of the pump causes. Loosen the drain plug of the fuel filter and push the priming pump to drain the water in the sedimenter.

Diesel EngineInjection Nozzles

1. Description

The injection nozzle converts the high-pressurized fuel, which is sent from the injection pump, into a mist by injecting the fuel into the combustion chamber. The diesel engine directly injects the fuel into the combustion chamber, which is different from the gasoline engine which makes the air-fuel mixture in advance. Thus, the time for mixing with the air is much shorter. Therefore, the fuel is injected at high pressure and high speed to create a mist that mixes easily with the air, thus improving the ignition performance.

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