Aspark-ignition engine (SI engine) is aninternal combustion engine, generally apetrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from aspark plug. This is in contrast tocompression-ignition engines, typicallydiesel engines, where the heat generated fromcompression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.
Spark-ignition engines are commonly referred to as "gasoline engines" in North America, and "petrol engines" in Britain and the rest of the world.[1] Spark-ignition engines can (and increasingly are) run on fuels other thanpetrol/gasoline, such asautogas (LPG),methanol,ethanol,bioethanol,compressed natural gas (CNG),hydrogen, and (in drag racing)nitromethane.[2]
The working cycle of both spark-ignition and compression-ignition engines may be eithertwo-stroke orfour-stroke.
Afour-stroke spark-ignition engine is anOtto cycle engine. It consists of following four strokes:suction or intake stroke,compression stroke,expansion or power stroke,exhaust stroke. Each stroke consists of 180 degree rotation of crankshaft rotation and hence afour-stroke cycle is completed through 720 degree of crank rotation. Thus for one complete cycle there is only one power stroke while the crankshaft turns by two revolutions.
