Two Stroke and Four Stroke Engines:

In  the two stroke engines thermodynamic cycle is completed in One revolution of crank shaft whereas in 4 stroke engines the cycle is completed in 2 revolutions of crank shaft. For same capacity and speed nearly 2 times power is developed in 2 stroke engine as compared to 4 stroke engine. But as high compression ratios cannot be achieved in 2 stroke engines, the efficiency of 2 stroke engine is less as compared to 4 stroke engines. Furthermore, the engines can be classified as Spark Ignition engines that operate with the petrol as fuel and Compression ignition engines that operate with diesel as fuel.