Compression ratios / Compressed gas in the cylinder / Gas laws

[sanioll]

Please read this, if you would like:zerothread?id=119832

whole point of above linked thread is to find out temp difference when a gas is compressed. We're trying to find out:

Ex; say you have a 600 cc cylinder (one of ka24de cylinders). Let say you compress the air/fuel mixtire to half; so now the piston is sitting in the middle. Size is 300cc.

What changes here:

VOLUME: from 600cc to 300 cc ??TEMP: has been increased.

I have looked into some stuff that we all learn in high school. PV=nRT.

P=pressureV=volumenR = is constantT = temperature

1) I am confused about something though. When using this formula (PV=nRT) does volume change when we compress the gas in the cylinder. assuming origional volume was .6 liters (600cc), now if cylinder is sitting in the middle, we have compressed the air it to the middle or half. Is the volume 600cc now, or 300cc?

.6 liters are now sitting in .3 liters of space. Do we consider it .3 liters and use it in the formula as .3 liters or not??

2) we need to know how to find out temperature increase vs compression ratios. is there any formula to plug in compresion ratio, given origional intake charge temp, volume(if turbocharged at 7 psi, 900cc in this case) etc, and get a final temperature after the compression. At top dead center?

This will bring us to main topic of how much boost can you run at the highest possible compression ratio(with a decent air/fuel ratio), without pre-spark detonation.

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I'd really appreciate anyone's intelligent responces. Engineering student myself, but new to engine world, so go easy on me. thanks.

[maxnix]

Probably need to do a search on BMEP. Static compression not a good model for understanding dynamic engine operation.

[Q45tech]

http://www.engr.colostate.edu/....html

[maxnix]

Great link. Too bad the acceleration applet is down.

[scoobas]

when applying theoretical science to engines you need to consider all the variables your cooling system oiling system running temperature detonation at higher running temps also consider the the intake charge at high revs you'll find in a NA engine you have less than 1bar pressure, how much less depending on valve size intake shape and size so consider ALL the variables in the given engine cause theory doesn't always apply to practical application for every different engine, plus lpg has a higher detonation temp then methanol higher again (25:1 is doable in na engine)