Quote:
Originally Posted by abently
I have to disagree with this statement. Oxygen alone does not provide useful energy. Remember anything beyond (leaner than) stoich means there is an excess of air within the cylinder just taking up space and therefore reducing power output.
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Disagree away all you want, but Old Mechanic was essentially correct.
One can model the power stroke of a 4-cycle engine as a thermodynamic process called adiabatic expansion. You can look it up on Wikipedia if you want, or search for "adaibatic process," but in any case, it can be shown that it does not matter how much air is inside the piston-cylinder arrangement, as long as the amount of energy input is the same.
In other words, you can burn a set amount of gasoline at stoich with a set amount of air, and you'll get a set amount of work extracted from the piston. Keep the gasoline constant, while increasing the amount of air inside the cylinder, and you'll still get the same exact amount of work out of the piston.
(I'm not going to go into heat losses into the metal, nor atmospheric drag losses acting on the piston, nor friction losses, or any intricacies about how gasoline ignites with air, because that would be missing the forest for the trees)