# Homework Help: Thermodynamics and Compression Ignition Pressure and Temp Problem?

1. May 29, 2012

### mm391

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. May 31, 2012

### rude man

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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