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Hmmm so stoichiometric definitely burns hotter than rich, that's clear. So it's down to why lean is hotter than rich.
So a rich mix will produce the same heat as stoichiometric, but the extra fuel will both cool and increase heat capacity, thus lower temperatures but same pressure (hmmm this is a rather big waste of fuel :O). So if it's quite rich then I can see the temperature going down a lot. A lean mix produces less heat but hmmm I can't see it being higher than stoichiometric, but the temperature would drop less for each increase in A/F ratio than it would drop if you were decreasing A/F by the same amount, since liquid fuel has a very high heat capacity compared to air. Does this sound right to people who actually tune cars?
@1660 I think theoretically you always want stoichiometric because the extra air doesn't do anything, but in real world situations burning lean is an easy way to reduce fuel consumption since other methods of limiting torque output generally sap a lot of energy. However if the engine is built with intake duration reduction or something that accomplishes that and it can expand the exhaust to near atmospheric pressure, you definitely do not want lean.
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