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Homework Help: How do you show the efficiency of an engine is x?

  1. Oct 27, 2012 #1
    1. The problem statement, all variables and given/known data
    A hypothetical engine, with an ideal gas as the working substance, operates in the cycle shown in the diagram, show the efficiency of an engine is :

    n= 1 - 1/[itex]\gamma[/itex] ((1-(P3\P1))/(1-(V3/V1)))

    The diagram is basically a section the bottom left quadrant of a circle with an adiabatic process for 3 to 1 to make it a cycle

    2. Relevant equations
    ΔU = Qout -Qcold - Work
    gamma = Cp/Cv

    3. The attempt at a solution
    I really have no idea how to start this
    Last edited: Oct 27, 2012
  2. jcsd
  3. Oct 27, 2012 #2


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    Hi lilliebeth. Welcome to PF. To be sure of how you are labeling the states 1, 2, and 3 could you please answer the following?

    The process from 1 to 2 is what type of process? (constant volume, constant pressure, or what?)
    Does heat flow in or out of the engine in going from 1 to 2?

    The process from 2 to 3 is what type of process?
    Does heat flow in or out of the engine for this process?

    To get started, you should add another relevant equation: the equation for the efficiency of an engine. That will help you decide what you need to calculate.
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