Work Done By Engine/Heat Engine

  • Thread starter EngNoob
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38
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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.
 

Answers and Replies

95
0
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.
 
38
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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
 
62
2
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.

Slide44.GIF

Slide51.GIF

Thanks,

Gordan
 
Last edited:

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