injection system. The air and fuel then mix in thecombustion chamber (fig. 1-8).4. The engine speed and the power output of adiesel engine are controlled by the quantity of fueladmitted to the combustion chamber. The amount of airis constant. On the gasoline engine, the speed and poweroutput is regulated by limiting the air and fuel mixtureentering the engine (fig. 1-9).A diesel engine is much more efficient than agasoline engine, such as the diesel engine does notrequire an ignition system due to the heat generated bythe higher compression, the diesel engine has a betterfuel economy due to the complete burning of the fuel,and the diesel engine develops greater torque due to thepower developed from the high-compression ratio.The strokes that make up the four-stroke cycle of adiesel engine follow.DIESEL ENGINE INTAKE STROKE.— Thepiston is at top dead center at the beginning of the intakestroke, and, as the piston moves downward, the intakevalve opens. The downward movement of the pistondraws air into the cylinder, and, as the piston reachesbottom dead center, the intake valve closes (fig. 1-10,view A).Figure 1-10.—Four-stroke cycle diesel engine.1-7
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