Chapter 5 Diesel Fuel Systems

CHAPTER 5 DIESEL FUEL SYSTEMS LEARNING OBJECTIVE: Describe the different type of diesel fuel systems, how the components function to provide fuel to the engine in proper quantities, and servicing of the diesel fuel systems. Maintenance personnel form part of an important network of dedicated people who ensure that medium- and heavy-duty trucks and construction equipment are kept in a state of safe and acceptable performance standards. The diesel fuel injection system is a major component of a properly operating engine. An engine out of adjustment can cause excessive exhaust smoke, poor fuel economy, heavy carbon buildup within the combustion chambers, and short engine life. DIESEL FUEL SYSTEMS LEARNING OBJECTIVE: Identify the properties of diesel fuel. Describe the function and operation of governors and fuel system components. Like the gasoline engine, the diesel engine is an internal combustion engine using either a two- or four- stroke cycle. Burning or combustion of fuel within the engine cylinders obtains power. The diesel engine does not use a carburetor because the diesel fuel is mixed in the cylinder with compressed air. Compression ratios in the diesel engine range between 14:1 and 19:1. This high ratio causes increased compression pressures of 400 to 600 psi and cylinder temperature reach 800°F to 1200°F. At the proper time, the diesel fuel is injected into the cylinder by a fuel injection system, which usually consists of a pump, fuel line, and injector or nozzle. When the fuel oil enters the cylinder, it will ignite because of the high temperatures. The diesel engine is known as a COMPRESSION- IGNITION engine, while the gasoline engine is a SPARK-IGNITION engine. Figure 5-1 shows the comparison of the four strokes of a four-cycle diesel engine and a four-cycle gasoline engine. The speed of a diesel engine is controlled by the amount of fuel injected into the cylinders. In a gasoline engine, the speed of the engine is controlled by the amount of air admitted into the carburetor or gasoline fuel injection systems. Mechanically, the diesel engine is similar to the gasoline engine. The intake, compression, power, and exhaust strokes occur in the same order. The arrangement of the pistons, connecting rods, crankshaft, and engine valves is about the same. The diesel engine is also classified as IN-LINE or V-TYPE. In comparison to the gasoline engine, the diesel engine produces more power per pound of fuel, is more reliable, has lower fuel consumption per horsepower per hour, and presents less of a fire hazard. These advantages are partially offset by higher initial cost, heavier construction needed for its high compression pressures, and the difficulty in starting which results from these pressures. DIESEL FUEL Diesel fuel is heavier than gasoline because it is obtained from the residue of the crude oil after the more volatile fuels have been removed. As with gasoline, the efficiency of diesel fuel varies with the type of engine in which it is used. By distillation, cracking, and blending of several oils, a suitable diesel fuel can be obtained for all engine operating conditions. Using a poor or improper grade of fuel can cause hard starting, incomplete combustion, a smoky exhaust, and engine knocks. The high injection pressures needed in the diesel fuel system result from close tolerances in the pumps and injectors. These tolerances make it necessary for the diesel fuel to have sufficient lubrication qualities to prevent rapid wear or damage. It must also be clean, 5-1