Spark ignition engine (SI engine): engine) An engine in which the combustion process in each cycle is started by use of an external spark.Internal combustion engines may be classified as : – Spark Ignition engines. – Steam engine is an example of external combustion engine, where the working fluid is steam. In an External combustion engine, working fluid gets energy using boilers by burning fossil fuels or any other fuel, thus the working fluid does not come in contact with combustion products.– Petrol engine is an example of internal combustion engine, where the working fluid is a mixture of air and fuel.
In an Internal combustion engine, combustion takes place within working fluid of the engine, thus fluid gets contaminated with combustion products.