# Work Done By Engine/Heat Engine

## Main Question or Discussion Point

Hi

Can some one help me out on how to calculate the work done by a cycle/heat engine?

I am looking to calculate this in a graphical form, using P-v diagram and a numerical form, using an equation of work.

I have state/process data for for cycle for volume an pressure for point 1-2/2-3/3-4/4-1.

I have a compression and expansion index.

If any one could help me out with the equation to use i would be real happy.

If anyone can point me in the direction of some further reading on this subject i would be greatful too.

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What kind of cycle? Get your air tables out and look up the enthalpy/energy values.
Then you calculate the net work as a sum of the difference in enthalpies for the points that generate or input work.

The Cycle would be "Otto" or "Diesel" heat engine.

I think i have the formulas.

Constant Volume: W = 0

Constant Pressure: W = P(V_2 - V_1)

Constant Tempreture: W = P_2 * V_2 * ln (V_2/V_1)

However, i am unsure if i am working with an ISOTHERMAL process vs POLYTROPIC process.

The pressure increases whilst the volume decreases, does this indicate Polytropic or Isothermal

Hi there:

Check out your post on compression and expansion.

The same material covers this post.

Here are two plots regarding the performance of Otto Cycle and Diesel Cycle.

Thanks,

Gordan

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