Spot on Oggers
At high compression the rate of the combustion reaction increases as the effective concentration of the fuel/air mix increases.
This happens because there is now a greater statistical probability of collisions at above or equal to the Energy of Activation for the reaction
Crucially we're back to time dependence. A more rapid reaction means more bangs per unit time and more power per unit time.
Why do we compress? To make the engine more powerful.
Carnot is predicated on the most efficient cycle for converting a given amount of thermal energy into work
Carnot cycle - Wikipedia, the free encyclopedia
CW