Air Standard Cycles

Introduction:

Due to the circulation of the working fluid inside the cycle Carnot Cycle, Stirling Cycle, Brayton Cycle are called closed cycles. And they are called external combustion engine because the addition of heat takes place externally in these cycles.
In our daily life we most commonly use practical engines are internal combustion engines for our vehicles, motorcycles, construction machineries, etc.

The internal combustion engines or IC engines are those in which the combustion of fuel takes place inside the engine. They are composed of piston and cylinder arrangement with suction and exhaust valves.

At the very beginning of the internal combustion cycle, the mixture of air and fuel is inducted inside the cylinder. A lot of heat is released when the fuel is combusted, which over heat the engine cylinder.
Hence to avoid the destruction of the engine , it is necessary to make engine cool either with water or with the external air.then the pressure of the gases also becomes very highhence pushes the piston producing work.
After that, the burnt gases are released to the environment as the exhaust gases and again the fresh mixture of air and fuel is injected inside the cylinder.
Because of releasing burnt gases and injecting fresh air, the internal combustion engines are said to be working in non-cyclic process.

Air Standard cycles and concept:

It doesn`t matter how the engine works (cyclic or non-cyclic), the analysis should be done on the input and output of the system.thus the air standard cycles was concieved to carry out those analysis.usually certain mass of the air is considered to be working inside the thermodynamic cycle and ideally all the processes are reversible.


Acctually, the internal combustion engines work on the principle of air standard cycles. The most commonly used air standard cycles are Otto cycle which corresponds to 4-stroke petrol or gasoline engine also called spark Ignition Engine and Diesel cycle which corresponds to 4-stroke Diesel Engines so called Compression Ignition Engines.