Thermodynamics: Air Standard Cycle solution

AIR STANDARD CYCLES

Because the working fluid does not go through a complete thermodynamic cycle in the engine (even though the engine operates in mechanical cycle) the internal combustion engine operates on the so called open cycle. However in order to analyze internal combustion engines, it is advantageous to devise closed cycles that closely approximate the open cycles. One such approach is the air standard cycle which is based on following assumptions:

1. A fixed mass of air of the working fluid throughout the entire cycle, and the air is always an ideal gas. Thus there is no inlet process or exhaust process.
2. The combustion process is replaced by a heat transfer from an external source.
3. The cycle is completed by heat transfer to the surroundings (in contrast to the exhaust and intake processes of an actual engine.)
4. All processes are internally reversible.
5. The additional assumption is usually made that air has constant specific heat.
   

The compression and power strokes of an internal combustion engine are the ones which account for much of its work output. The exhaust and intake strokes are up a small account of the work and form a small counterclockwise loop on P-V diagram.

Neglecting the lower bit part, the upper region (clockwise) is approximated as an Otto cycle with two isochores (V=C) and two isentropics (S=C)

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