Construction Equipment Diesel Fuel Systems Army Course on CD

INTRODUCTION

This subcourse is designed to teach the knowledge and skills necessary for performing tasks related to the adjustment, repair, or replacement of components of diesel fuel systems found on items of engineer construction equipment. The subcourse is presented in five lessons, each corresponding to a specific learning

The prime job 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 the diesel engine occurs when this charge of fuel is mixed with hot compressed air. No electrical spark is used (as in the 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 systems have the following components:

Fuel Tanks. There are many different types and shapes of fuel tanks. Each size and shape is designed for a definite requirement. 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. 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. The four major ways of injecting fuel are the individual pump and nozzle for each cylinder, pumps in a common housing with nozzles for each cylinder, a combined pump and nozzle for each cylinder (unit injector type), and 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 the crude oil that are left over after the more volatile fuels such as gasoline and kerosene are removed during the refining process. The Army uses No. 1 and No. 2 diesel fuel. 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 adjustments necessary when changing from one fuel to another. Efficient operation demands that fuel system components be maintained in first class condition at all times. Servicing the components of the diesel fuel system is not a difficult task and may be performed by the average mechanic. However, due to close tolerances of various parts of the fuel system, extreme cleanliness and strict adherence to instructions is required. A high percentage of failures occurs in the diesel fuel system due to carelessness or faulty workmanship.