Frustrated with Adiabatic compression problem

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The discussion revolves around a homework problem involving adiabatic compression in a diesel engine, specifically calculating the compression ratio needed for diesel ignition at 287°C. The student expresses frustration due to a lack of initial pressure and volume data, feeling uncertain about how to approach the problem. Respondents suggest using atmospheric pressure as a starting point and recommend assuming a convenient volume for calculations. This guidance aims to help the student overcome their confusion and proceed with the problem. Overall, the conversation emphasizes the importance of making reasonable assumptions in thermodynamic calculations.
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Homework Statement


In a diesel engine air is adiabatically compressed to autoignition temperature (287oC) of diesel. Given
C/nR=2.78 for air, and the room temperature is 27oC, what is the compression
ratio where diesel vapor is added for ignition.

Homework Equations



PV=nRT
PV=NkT
C=(dU/dT)

The Attempt at a Solution



I'm just frustrated with this review problem and think I may be over thinking it but I am not given an initial pressure or volume and so I am not sure where to even start with this problem. Could someone please give me a push in the right direction.
 
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sfgoat said:
I'm just frustrated with this review problem and think I may be over thinking it but I am not given an initial pressure or volume and so I am not sure where to even start with this problem. Could someone please give me a push in the right direction.

Well, most diesel engines take their combustion air from the atmosphere, so what is the pressure there?

If you want a volume to work with, assume one: a liter, a cubic meter, whatever you feel comfortable with.
 

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