Figure 1-10.—Four-stroke cycle diesel engine.

injection system. The air and fuel then mix in the combustion chamber (fig. 1-8). 4. The engine speed and the power output of a diesel engine are controlled by the quantity of fuel admitted to the combustion chamber. The amount of air is constant. On the gasoline engine, the speed and power output is regulated by limiting the air and fuel mixture entering the engine (fig. 1-9). A diesel engine is much more efficient than a gasoline engine, such as the diesel engine does not require an ignition system due to the heat generated by the higher compression, the diesel engine has a better fuel economy due to the complete burning of the fuel, and the diesel engine develops greater torque due to the power developed from the high-compression ratio. The strokes that make up the four-stroke cycle of a diesel engine follow. DIESEL ENGINE INTAKE STROKE.— The piston is at top dead center at the beginning of the intake stroke, and, as the piston moves downward, the intake valve opens. The downward movement of the piston draws air into the cylinder, and, as the piston reaches bottom dead center, the intake valve closes (fig. 1-10, view A). Figure 1-10.—Four-stroke cycle diesel engine. 1-7