The thermodynamic cycles like Carnot cycle, Stirling cycle, Brayton cycle are closed cycles as the working fluid keeps on circulating inside the cycle. In these cycles the addition of heat takes places externally, hence they also called external combustion engines. The most commonly used practical engines used in our day-to-day life are internal combustion engines for our vehicles, motorcycles, construction machineries etc.
The engines in which combustion of fuel takes place inside the engine are called as internal combustion engines or IC engines. The IC engines comprises of the piston and cylinder arrangement with suction and exhaust valves.
In the beginning of the internal combustion cycle, the air-fuel mixture is inducted inside the cylinder. When the fuel is combusted lot of heat is released which makes the engine cylinder very hot. To avoid the deterioration of the engine, it is very important to cool the engine either with water or with external air. After combustion of fuel the pressure of gases becomes very high which pushes the piston producing the work. Thereafter the burnt gases are released to the atmosphere as exhaust gases and the fresh air-fuel mixture is inducted inside the cylinder. Since the burnt air-fuel mixture does not moves into the cycle again and fresh air-fuel mixture is inducted at the beginning of each cycle, the internal combustion engines are said to be working in non-cyclic process.
