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Thermal Efficiency

  1. Mar 26, 2008 #1

    Could any one help me with this?

    How would i go about calculating the thermal efficiency of a heat engine with four processes?

    I am thinking of moddeling it on the Otto or Diesel Cycle.

    The data i have is.

    Temp @ State/Process 1

    Specific Gas Constant

    Specific Heat Capacity

    and i have



    for states one, two, three and four.

    How would i got about figuring out the thermal efficiency? do i use a NFEE equation?

    Thanks for any help.
  2. jcsd
  3. Mar 26, 2008 #2
    Although my knowledge is limited on the subject, I assume that if the working fluid is air, then you would need some air tables to look up the enthalpy/internal energy values for each state. Once you have those values you can calculate the net work and the heat input to the engine. Your efficiency then is the ratio of the two.
  4. Mar 27, 2008 #3
    See how much heat is transfered at the high temperature (Qh) then see how much heat is transfered at the low temperature (Qc), then use

    n (thermal) = (Qh-Qc)/Qh or W/Qh
  5. Mar 27, 2008 #4
    Thanks for that, i will have a go using that formula.

    However, i need to calculate work done first for a otto cycle, any ideas on that?

    I have Volume, Pressure and Exp/Comp Index
  6. Apr 7, 2008 #5
    Hi there:

    Check out your post on compression and expansion.

    The same input material covers this post.

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




    Last edited: Apr 7, 2008
  7. Apr 11, 2008 #6
    Thanks for that, understand better now, cheers...
  8. Apr 11, 2008 #7

    I am glad to be of some help to you and PF members and/or visitors ...


  9. Apr 11, 2008 #8
    Hi, I'm new by here.
    The information helps.I will see something about jet engines.
    But, just to make presence, leave a reply.Ok?
    See you later.
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