DIESEL FUEL SYSTEMS

Introduction
The function of the diesel fuel system is to inject a precise amount of atomized and pressurized fuel into each engine cylinder at the proper time. Combustion in a diesel engine occurs when this charge of fuel is mixed with hot compressed air. No electrical spark is used (as in a gasoline engine).

The diesel fuel injection system must supply the correct quantity of fuel, time the fuel delivery, control the delivery rate, atomize the fuel, and distribute the fuel evenly through the cylinder. The fuel system has the following components:

Fuel Tanks
There are many different types and shapes of fuel tanks. Each size and shape is designed for a specific purpose. It must be capable of storing enough fuel to operate the engine for a reasonable length of time. The tank must be closed to prevent dirt from entering. It must also be vented to allow air to enter, replacing the fuel used. Three other tank openings are required--one to fill, one to discharge, and one to drain.

Fuel Lines
There are three types of diesel fuel lines. These include heavy weight lines for very high pressure between the injection pump and the nozzles, medium weight lines for light or medium fuel pressures between the tank and injection pump, and light weight lines where there is little or no pressure.

Fuel Filters
Diesel fuel must be filtered not once, but several times in most systems. A typical system might have three stages of progressive filters--a filter screen at the tank or transfer pump, a primary fuel filter, and a secondary fuel filter. In series filters, all the fuel goes through one filter and then through the other. In parallel filters, part of the fuel goes through each filter.

Fuel Transfer Pumps
Simple fuel systems use gravity or air pressure to get fuel from the tank to the injection pump. On modern high speed diesel engines, a fuel transfer pump is normally used. This pump, driven by the engine, supplies fuel automatically to the diesel injection system. The pump often has a hand primer lever for bleeding air from the system. Modern injection pumps are almost all jerk pumps which use the plunger and cam method of fuel injection.

There are four major ways of injecting fuel:
1) Individual pump and nozzle for each cylinder
2) Combined pump and nozzle for each cylinder (unit injector type)
3) Pumps in a common housing with nozzles for each cylinder (common rail system)
4) One pump serving nozzles for several cylinders (distributor type)

The unit injector pump is common on larger engines, while the in-line and distributor types are used on off-the-road farm and industrial machines.

Injection Nozzles
The injection nozzle must atomize the fuel for better combustion and spread the fuel spray to fully mix it with air. In addition, all nozzles in multicylinder engines must inject fuel equally for smooth power. Nozzles are simple devices. They use a spring to oppose fuel pressure until the right instant for injecting fuel, when the nozzle valve opens. The injector nozzle is the bottom section of the fuel injector.

Diesel Fuels
The fuels used in modern high speed diesel engines are derived from the heavier residues of crude oil that are left over after the more volatile fuels such as gasoline are removed during the refining process. The two most common grades of diesel fuel are No. 1 and No. 2. In normal operations, No. 2 diesel fuel is used during the warm months with a change to No. 1 for winterization purposes. There are no engine adjustments necessary when changing from one fuel to another.

Water
A common enemy of diesel fuel systems is water. Unfortunately, water is more common in diesel fuel than most people realize. Should water find its way into an injection system, it will rapidly oxidize ferrous metal (steel) components. Some of the most common failures attributed to water include:

• Injection component seizure (Failure)
• Sticky metering components in both the pump and nozzle
• Governor/metering component failure

Conclusion

A diesel fuel system is a critical component of any diesel engine and its optimum operation is essential for peak performance. E-ZOIL manufactures several additives formulated to address common issues faced by the diesel fuel system. DIESEL AID will totally disperse water preventing pure water from traveling through the fuel system and causing severe damage. DIESEL AID, ARTIC POWER, and CLEAN & LUBE will increase overall fuel system lubricity preventing premature failure of the fuel pump and injectors.