Mixture and EGT

[robert dingli]

Hi all,

I've been waiting for some labs results to empirically answer the original 
query about EGTs vs AFR.  Our test rig (Lancia 2lt 16V on motoring 
dynamometer) is wired with a thermocouple in each exhaust runner and one 
in the collector.  (It also has thermocouples in every other nook and 
cranny.)  We have also individually plumbed each runner to the exhaust gas 
analyser for CO, CO2, O2, HC and NOx measurements.  I will post some EGT 
characteristics soon.

> 
> My understanding is that combustion temperature is highest at stoich and
> declines as mixture is made richer or leaner. Question: why is EGT increasing as
> mixture is leaned. Is it because combustion temp is increasing as rich
> mixture is brought nearer to stoich? Is it because lean mixture burns
> slower and is still burning as the exhaust valve opens. Or none of the
> above?
> 
> Thx, Harmon
>