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Work Done By Engine/Heat Engine

  1. Mar 26, 2008 #1

    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.
  2. jcsd
  3. Mar 26, 2008 #2
    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.
  4. Mar 27, 2008 #3
    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
  5. Apr 7, 2008 #4
    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.




    Last edited: Apr 7, 2008
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