How to use air/fuel ratios as a tuning tool

Turbocharged engines are a double-edged sword. More power is readily available through more boost, but so is more disaster. So, when you even vaguely consider adding boost to an engine, you need to have a plan to at least monitor the other factors that will be affected by this additional air. Most notably, this means keeping an eye on how …

Read the rest of the story

I'm not a chemical engineer, but I do enjoy the science behind the scenes.

<< Complete burning of the fuel means less atomized liquid fuel in the combustion chamber, which means less cooling of interior combustion surfaces, which means more energy lost as heat, for example. >>

i don't follow this...

any heat not converted to pressure to push the piston down is a decrease in efficiency, yes?  And any fuel not burned also decreases efficiency.

my "understanding " of rich mixtures under high load was to use the un burnt fuel as a coolant...absorbing heat...from the piston dome and exhaust valve....to prevent pre ignition and burnt valves.

Any thoughts?

and, I believe that a catalyst promotes or speeds up a chemical reaction, but is not consumed in the reaction...so oxygen would not qualify as a "catalyst", yes?

In reply to BimmerMaven :

Yep I agree. Oxygen is not a catalyst in the combustion process it is a reactant.

A rich mixture does lower combustion temp, partly due to the heat of vaporization of the excess fuel, but mostly because of the less hot combustion process of burning 2 HC + O2 = H2O & CO. A stoich mixture burns to CO2 which releases more heat & power.

In reply to BimmerMaven :

The rich mixture doesn't cool surfaces as much as it keeps the peak combustion temp down. Which then keeps surfaces less hot. 
 

That being said, modern materials are almost magic- one of my last projects was to improve the CO emissions on a very boosted product. Which really means run less rich. Many modern engines can run a really long time at stoich under max boost, pushing exhaust temps past 1800F.