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Thermodynamics and Compression Ignition Pressure and Temp Problem?

  1. May 29, 2012 #1
    1. The problem statement, all variables and given/known data

    A model diesel C.I engine has a volumetric compression ratio of 18:1 and a cut*off ratio of 1.5:1?
    The engine has a volumetric compression ratio of 18:1 and a cut*off ratio of
    1.5:1.

    If p1 = 1 bar and T1 = 27°C, determine the pressure and temperature
    at each point in the cycle.

    How would I do this?

    2. Relevant equations

    p1V1/T1=p2V2/T2

    p1V1^n=p2V2^n



    3. The attempt at a solution

    T2 = 18^(1.4-1)*300 = 954K

    No idea how to work out the pressures. I know it is isentropic so p1V1^n=p2V2^n
     
  2. jcsd
  3. May 31, 2012 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    The Diesel cycle consists of the following:
    1. adiabatic (isentropic) compression from p1 v1 to p2 v2
    2. isobaric expansion from p2 v2 to p2 v3
    3. adiabatic expansion from p2 v3 to p4 v1
    4. isochoric (constant-volume) decompression from p4 v1 to p1 v1.

    Just use the ideal gas relation pv = RT to get all the above p's and v's.
    Realize that compression ratio = v1/v2 and cutoff ratio = v3/v2.
     
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