TABLE OF CONTENTS The process of combustion in a diesel engine differs from that in a petrol engine and therefore the two must be considered separately.
Air and fuel are drawn into the cylinder and compressed into the combustion chamber by the rising piston. Just before TDC a spark at the spark plug ignites the mixture which burns rapidly across the combustion chamber in a controlled manner.
Air only is drawn into the cylinder and compressed by the rising piston. The compression pressure, and therefore the temperature of the air, is very much higher in the CI engine than in the SI engine. Fuel in the form of very fine droplets is injected into the cylinder; towards the end of the compression stroke this fuel heats up and self-ignites. This causes a very rapid temperature and pressure rise forcing the piston down on its power stroke. The amount of fuel injected will determine the power developed by the engine.
Figure 1.10 shows the layout of a single-cylinder engine. The reciprocating motion of the piston is converted to rotary motion of the crankshaft by the connecting rod.
As the piston moves downwards the connecting rod is forced to move the crankshaft in a clockwise direction. In this way the linear (straight line) motion of the piston is converted into rotary motion of the crankshaft
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