Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What equation would be used to estimate the temperature?

  1. Jan 26, 2004 #1
    Can someone help me get started on this question?:

    In a Diesel engine, atmospheric air is quickly compressed to about 1/20 of its original volume. Estimate the temperature of the air after compresion and explain why a Diesel engine does not require spark plugs.


    What equation would be used to estimate the temperature?
     
  2. jcsd
  3. Jan 26, 2004 #2

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Use the adiabatic condition [itex]\left(PV^\gamma = \textit{constant}\right)[/itex] to find the pressure in the cylinder after the volume has been reduced to 1/20 of its initial volume.

    Next, use the ideal gas law [itex]\left(PV = nRT\right)[/itex] to calculate the temperature.

    - Warren
     
  4. Jan 27, 2004 #3

    turin

    User Avatar
    Homework Helper

    chroot, how do you know it's adiabatic? Is this an approximation? I don't see how heat is prevented from transfer to the cylinder wall.
     
  5. Jan 27, 2004 #4

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The key word is "quickly." Given that the compression happens quickly, not enough time is available for significant heat transfer to occur.

    - Warren
     
  6. Jan 28, 2004 #5

    turin

    User Avatar
    Homework Helper

    Thanks chroot. That's exactly the kind of clarification I was looking for, and it makes sense to me now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?