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EGT rises when carb heat applied

B

Bob_pipedream

Active Member
Hi all,

Mentioned this in other posts, but am having issues trying to find an answer.

Why would EGT rise when Carb heat is applied?

The only logic I can come up with is that I am operating LOP and do not realise it...

Really getting confused by conflicting issues here!
 
EGT rises for the same reason RPM falls, a hotter air charge (thus, less dense air charge) is entering the carb, thus causing you to run leaner than you were before carb heat was applied.

Leaner mixture = higher EGT
 
???

If the fuel flow remains the same and inlet air temp increases (carb heat), the engine will run richer, not leaner. Maybe the richer mixture is still burning when the exhaust valve opens, heating the probe more.
 
KRviator said:
EGT rises for the same reason RPM falls, a hotter air charge (thus, less dense air charge) is entering the carb, thus causing you to run leaner than you were before carb heat was applied.

Leaner mixture = higher EGT
Click to expand...

Is this not backwards? A less dense, hot air SHOULD make for a richer mixture, no? Colder, more dense air would make the mixture leaner, IMO.

Best,
 
You are increasing the starting temperature of the fuel/air mixture in the cylinder by what, maybe 75 degrees? Then you are still introducing the same amount of heat as before by burning the fuel. It stands to reason the final exhaust gases will be a little hotter, by about the same margin as the original charge air increase.
 
One more theory

Are ALL the EGTs rising? One practice I've heard of is that application of at least partial carb heat leads to better vaporization of the fuel/air mixture and a more even distribution to the individual cylinders through the manifold. Better atomization and distribution could lead to more complete combustion and a subsequent rise in EGT.

Just a thought...

Don
 
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