Engine engineering question

I have a couple questions that I am hoping can be answered by experts (and I mean that) that support these boards.

When my U302 comes up on compression when running, what is normal average cylinder pressure?

If it could be measured, after fuel ignites and pressure in cylinder reaches max, what is that average?

Now lastly, when a piston comes to bottom after power stroke it would have to have some small amount of pressure still in cylinder.

Last time it was at bottom it was filled with air and fuel at I am guessing normal atmospheric pressure.

All that is still there except burned and expanded so pressure would have to be higher than before burn.

Before exhaust valve opens what is happening at that bottom stroke?

In my mind, I would think one that used all expanded energy before exhaust valve opens would be most fuel efficient.

Lastly how does engineers designing engines view all this? It seems a trade on one area requires a change in another or it doesn't seem I know it would. Laws of physics works across all disciplines of science.

Thanks,

Daniel

Why do I want to know all this? No reason, I just do. I am a computer science/electrical engineer by trade but I have been fascinated with these questions in my head since growing up on a farm where my Dad had a 1966 Super Jet.
 
First question would be gas Lp or diesel. Gas or lp used different heads so lp has higher compression. 120 gas 170 lp 440 diesel.
 
(quoted from post at 09:01:50 10/12/19) First question would be gas Lp or diesel. Gas or lp used different heads so lp has higher compression. 120 gas 170 lp 440 diesel.

When I wrote this I guess I was thinking of gas but its a good thought for all engines.

I did not realize LP was higher compression over gas.

Seems they would want all types to be as high as possible to get most bang from fuel.

It is all very interesting. Also I suspect not 100 percent of fuel is completely burned before power stroke is finished.
 
Just a note: The pressures stated are at starter cranking speed for a compression test. The OP stated with engine running which would be higher but those numbers are not available. I have never heard of checking compression with the engine running. An engineer that works with engine design may know the answer.
 
Good questions. I found a chart but
couldn't read it very good. What I did
find was modern diesels peak pressure is
170 bar. Or 2467 psi.
 

Yes this question had to do with pressures in cylinder when running not compression tests.

Cylinder gets loaded up with gas and oxygen and then a spark.

When running and under load with everything working as should, I am wondering what pressures are reached in cylinder after ignition of fuel.

Again this is not about compression testing of a cranking motor.

Thanks.
 

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