Spark Ignition Engines (or S.I. Engine):
It works on otto cycle. In Otto cycle, energy supply and rejection occur at the constant volume process and compression and expansion occur isentropically. The engines working on the Otto cycle use petrol as fuel and incorporate carburetor for the preparation of mixture of air fuel vapor in the correct proportions for rapid combustion and spark plug for ignition of mixture at the end of compression. The compression ratio is 5 to 10.5. Engine has usually high speed as compared to C.I. engine. Low maintenance cost but elevated running cost. These engines are called as spark ignition engines or S.I. Engine simply.