Fuel System:

All diesel engines need a technique to deliver and store fuel to the engine. Since diesel engines rely on injectors that are precision elements along with extremely tight tolerances and extremely small injection hole(s), a fuel delivered to the engine must be very clean and free of contaminants.

Figure: Diesel Engine Fuel Flowpath

The fuel system must, thus, not only deliver the fuel but also ensure its cleanliness. This is commonly accomplished by a series of in-line filters. Generally, the fuel will be filtered at one outside the engine and after that the fuel will pass by at least one more filter internal to the engine, commonly located within the fuel line at each fuel injector.

In a diesel engine, a fuel system is much more complex than the fuel system on an easy gasoline engine since the fuel serves two purposes. One reason is obviously to supply the fuel to run the engine; another is to act as a coolant to the injectors. To meet this second reason, diesel fuel is kept continuously flowing by the engine's fuel system at a flow rate much higher than required to simply run the engine, an instance of a fuel flowpath is display in Figure. The excess fuel is routed back to the fuel pump or the fuel storage tank that is depending on the application.