<... when the engine compresses it before ignition. My thought
was that a 100 degrees could be small
potatoes by comparison ...>
TT says CHARGE TEMP IS EVERYTHING. You need to keep that thought.
The reason you're turbocharging in the first place is to get more (greater
mass of) air into the combustion chamber. That done, the magic happens
and the prop turns faster. The hotter the intake temp, the less charge
you deliver to the chamber. You don't give a rat's ass what compression
temps are (so long as they don't detonate - but that's another issue).
Compression temps are the rotor's job. Delivering the greatest amount
of air you can with the least effort on the part of the engine is your
job. Just keep on delivering the mostest, coldest air you can to
the chamber. That's your job. The rest of that stuff is the
rotor's job, and we'd do well to leave him alone and let him do it.
Just tryin' to stay focused .... Jim S.
Russell Duffy wrote:
Still
have the old turbo bug but haven't run it in 8 years as I have an airplane
to fly now. Ken WelterAre
we going to have to call you Herbie now :-) Thanks
for the real world (if you can call 100" MAP real world) failure modes.
Hopefully, I'll be a little safer at half that.And
now, for more turbo math. With all the talk of intake temps, I was
wondering just how hot the mixture gets when the engine compresses it before
ignition. My thought was that a 100 degrees could be small potatoes
by comparison. Calling on all of my vast memory from Physics about
an eon ago, I searched internet until someone handed me the formula on
a silver platter :-)The
formula is: (intake temp in Kelvin) * (compression ratio) ^ (gamma
-1)gamma
is listed as 1.4 for gas engines.For
a 90F day, and 9.7 cr, we have 305 * 9.7 ^.4 = 757 K or 903
degrees F (ouch)At
first, I though this was good news, until I found out that raising intake
temp 100 degrees, raises the compression temp much more than 100. At
my 5 psi intake temp of 214, the compression temp is 1210 F.This
is all interesting, but doesn't tell me diddly. First, the actual
intake temp is probably a good bit lower, since fuel atomization will lower
the charge temp from what we measure before the throttle body. Second,
octane, timing, mixture and engine cooling have a large part to play in
where detonation will occur. The
lesson to be learned here is that you should just delete my posts when
you see them :-)Cheers, Turbo
Rusty
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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