Scott:

As an example, in my Twin Beech, when the OAT is 92dF, the temperature AFTER the venturi in the carburetor is 35dF. That temperature drop across the venturi is not there in an injected engine. Now add another 100dF so that the IAT is 192 and the carb temp is 135. That is not a good thing. At high powers, with higher CHTs, the detonation margin is quite a bit narrower. This isn't too much of a problem in the lower compression engines but can quickly cross the threshold in the higher compression engines.

If you draw a higher (by 100dF) IAT when the OAT is very cold, it's not a big deal--the engine just thinks it's summer time! If you do that during the summer, when the OAT is already high, it could quickly become an issue in the higher compression engines. By the time one adds 9 or 10:1 pistons, it can get ugly quickly.

This effect is why we think intercoolers are so important.

Walter


On Aug 5, 2005, at 6:33 AM, Sky2high@aol.com wrote:


In a message dated 8/4/2005 4:15:47 P.M. Central Standard Time, marv@lancaironline.net writes:

I think you might
find that any reduction in IAT from fuel vaporization at the cylinder
induction port will be insignificant.

Walter,
 
Hmmmmm....  You were quite willing to point out earlier that the final induction air temperature in a carburetor  remained quite low (the FAA requirement is what, a 50F, 80F min rise from carb heat as measured after vaporization?)  even though I now know that the searing temperature of air from the heat muff raises the pre-vaporization air temp quite a bit.
 
I guess the only thing to do insert a probe in the cylinder just after injector vaporization or do a calculation (now my head is hurting) on gas  cooling effects.
 
If only my copy of Taylor, Vol 1 would get here.
 
Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)