Where did you get that information? I want to learn more....

Minh-Thanh, I hope Peter doesn't mind me stepping in here, but I will do my best to present the math for the thermodynamics of air compression.

First, an assumption regarding the type of compression must be made. With fast compression as in an engine, the process is normally considered to be adiabatic, such that as the air is compressed, all of the heat of compression stays in the compressed air, and none is lost to the cylinder walls. (This assumes that the heat lost from an engine is from combustion, not the compression.) An isothermal compression process is where the air is slowly compressed such that all of the heat of compression is lost thru the cylinder walls. Full isothermal compressions are rare, and the compression process is often somewhere between adiabatic and isothermal.

Confusing, yes, but we will go with full adiabatic compression.

Finding the final pressure and temperature is a 2 step process.

Here are the terms:

Starting volume V1 and final volume V2. we will use cc's.

Starting and final pressure P1 and P2. we will use Bar.

Starting and final temp T1 and T2. we will use degrees Kelvin.

Specific heat ratio for air, called gamma, is 1.4 for air (adiabatic process) but can vary all the way down to 1.0 for a true isothermal process. We will use a gamma =1.4

I will write the formulas as in an excel spreadsheet., but with extra parentheses for clarity.

Step 1. starting volume V1 and final volume V2.

This is easy. For a diesel at 20 to one compression, say the volumes are:

V1=20cc and V2=1cc

CR= V1/V2=20

Step 2. starting pressure P1 and final pressure P2.

This is more difficult. P2 varies with the value of gamma.

P2=(P1*(V1^1.4))/(V2^1.4)

Let's say P1is one Bar (14.7 psi)

P2=(1*(20^1.4))/(1^1.4)

P2= (1*(67.17)/(1)

P2= 67.17 Bar (974 psi)

Step 3. starting temp T1 and final temp T2. (must use the Kelvin scale)

You must choose a starting air temp. Let's call it 90 deg F = 305 deg K

T2=(P2*V2*T1)/(P1*V1)

T2= (67.17*1*305)/(1*20)

T2= 1012K (1362F)

Please note that T1 starting air temp and the value of gamma can have quite an impact on the final temp T2. That is why sometimes the data from different charts might not appear to match.

I hope I didn't make too many typos, but please let me know if I did.

Peter, I hope you concur and don't mind me hoping in here.

Lloyd