The diesel fuel system’s function is to precisely inject the right amount of atomized, pressurized fuel into each engine. This mixture of hot compressed air and fuel creates combustion in a diesel engine. A gasoline engine does not use an electrical spark.

These are the components of the fuel system.


There are many types and shapes to choose from when it comes to fuel tanks. Each fuel tank is made for a specific purpose. The fuel tank should be capable of holding enough fuel to run the engine for a reasonable time. To prevent foreign objects from contaminating the tank, it must be sealed. Ventilation is also required to let air in, which will replace any fuel used by the engine. There are three other tank openings: one to fill, one for discharge and one to drain.


There are three types of diesel fuel lines. There are three types of diesel fuel lines: heavyweight lines to handle the high pressures between the injection pump & the injectors; medium weight lines to handle the low or medium fuel pressures between the fuel tank & injection pump; and lightweight lines that carry little or no pressure.


Most diesel fuel needs to be filtered multiple times. A typical system may have three stages or more progressive filters: a filter screen at the tank/transfer pump, a primary fuel filter, and another secondary fuel filter. All fuel passes through a series filter. Parallel filters allow for a portion of the fuel to pass through each filter.


Simple fuel systems use gravity and air pressure to transfer fuel from the tank to an injection pump. A fuel transfer pump is used on modern high-speed diesel engines. The engine drives the pump and it supplies fuel to the diesel injection system automatically. A hand primer lever is often included on the pump to drain excess air from it. Modern injection pumps almost exclusively use the plunger-cam method of fuel injection.


There are four main systems that inject fuel.

  • Each cylinder has its own pump and injector
  • Each cylinder has a combined pump and injector (unit injector type).
  • One pump serving injectors for several cylinders ( distributor type )
  • Pumps in a common housing, with injectors for every cylinder ( common rail system).

Common rail is quickly becoming a popular option for many on-road applications. Both the in-line and distributor types can be used on offroad vehicles as well as industrial machines.

High-Pressure Common Rail Fuel System


The most critical components of fuel systems are diesel fuel injectors. The injectors are responsible for delivering the right amount of atomized, pressurized fuel to each cylinder. High-atomized, pressurized fuel is evenly distributed throughout each cylinder, which results in greater power and fuel economy, reduced engine noise, and smoother operation.

Modern diesel fuel injectors use piezoelectricity, similar to those used in common rail fuel systems. Piezoelectric injectors can handle high pressures in common rail applications and are very precise.


Modern high-speed diesel engines use heavy crude oil residues that have been left over from the removal of volatile fuels like gasoline. 2-D is the most popular diesel fuel, also known as ultra-low-sulfur diesel (ULSD).


Water is a common enemy of diesel fuel systems. Water is a more common ingredient in diesel fuel than people realize. If water finds its way into the injection system, it can quickly oxidize ferrous metal components. Water is responsible for many of the most common problems.

  • Injection component seizure
  • Sticky metering parts in the injector and pump
  • Governor/metering component failure

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