
Originally Posted by
mxrz
Yes, engine efficiency can be explained by physics, it's called thermodynamics, and more precisely reaction stoichiometry, but you're still only working with quantative relationships between fuel and air during combustion. These known, and measurable relationships are derived from chemistry, which is at the most basic level of the problem in question.
Ehh, I have to agree and disagree. You're correct that chemistry is involved, but a heat engine's efficiency is determined by a more than just chemistry. Heat engines are designed for the purpose of converting other forms of energy to work, and their performance is expressed in terms of the thermal efficiency, which is the ratio of the net work produced by the engine (physics) to the total heat input (chemistry). Physics + Chemistry = Thermodynamics.
If you really want to get technical, a 4-stroke engine is based on the Otto Cycle. The thermal efficiency of the Otto Cycle is based on the compression ratio of the piston (physics) raised to the specific heat ratio minus 1 (chemistry).
Simply put, Thermal Efficiency of the Otto Cycle = 1 - (1/(r^(k-1))).
So, your evaluation of engine efficiency being based solely on chemistry isn't correct.
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