Indicated Power is defined as the power developed by combustion of fuel inside the engine cylinder. It is always more than brake power. Therefore, the difference between IP and BP indicates the power loss in the mechanical components of engine due to friction.

The most commonly used power plant in automobiles is an internal combustion engine (ICE). An internal combustion engine (ICE) is a type of heat engine that converts the chemical energy stored in fuel into mechanical energy. It works by burning fuel inside a combustion chamber to create a high-pressure and high-temperature gas that expands and pushes a piston, which in turn drives a crankshaft.

Otto cycle is also known as constant volume cycle, as the heat is received and rejected at a constant volume. Otto cycle is used in gas, petrol and many of the oil engines. The petrol engine works on Otto cycle. 

The ideal Otto cycle consists of two constant volume and two reversible adiabatic or isentropic processes. 

Otto cycle is taken as a standard of comparison for internal combustion engines. For the purpose of comparison with other cycles, the air is assumed to be the working substance.

A square engine is an engine with bore diameter equal to stroke length. D=L. An under-squared engine has stroke length greater than bore diameter (L >D). This means the engine generates more torque at low speeds. These can be found in heavy vehicles such as Harley Davidson.