REFLECTOR: EGT Temps

[Brian Michalk]

Scott Derrick wrote:
> lean cylinder where as with a MAG a good portion of it is burning on 
> the way out the tail pipe.  This premature loss of efficiency in the 
> leanest cylinders when the rich ones are lagging behind is what causes 
> the engine to run rough when you try to lean past peak to 50-75 LOP.

Pretty good.
The biggest problem with LOP operations, even with an engine in perfect tune
is that the swirling airflow inside the cylinder is chaotic.  A rich
cylinder burns very predictably, while a lean cylinder does not. 
This phenomenon is measured by CoV:  The coefficient of variability (Taylor,
et. al.).

As the mixture gets leaner, and also as the density increases, it becomes
more difficult to create a reliable spark, and also becomes more difficult
to establish a viable flame front.

A perfectly tuned engine running excessively LOP will run rough due to these
limitations.  This is where the stratified charge devices Honda plays with
come into play, or the Saab (I think) method of using two combustion
chambers; one rich that squirts a flame into the lean main chamber.  There
are also other ignition schemes to address this.  One is to detect the
presence of a flame kernel around the spark plug.  If there is no flame,
then keep sparking the plug.  The power pulse will be late, but it's better
than no power pulse at all.

Continuing to move to a leaner condition leads to progressively worse fuel
economy.  This is because a failed combustion event dumps that fuel
overboard, with no extraction of power.  At this point, you may see higher
EGT's as the mixture is ignited in the exhaust.