What two factors primarily determine the efficiency of an internal combustion engine?

The efficiency of an internal combustion engine is primarily determined by the maximum and minimum temperatures that the engine operates under. This concept is grounded in the thermodynamic principles described by the Carnot efficiency, which states that the efficiency of any heat engine is dependent on the temperature difference between its hot and cold reservoirs.

In the context of an internal combustion engine, the maximum temperature is typically related to the combustion process, where fuel ignites and generates high-pressure gases. In contrast, the minimum temperature is related to the point where the waste heat is expelled, usually through the cooling system. A higher maximum temperature, combined with a lower minimum temperature, results in a greater thermal efficiency, as more of the energy from the combusted fuel is converted into useful work, rather than wasted as heat.

Other factors, such as engine design and fuel type, do influence performance, but they are not the primary determinants of efficiency. The inherent thermodynamic limits set by temperature variations are the core factors that affect how efficiently an engine converts fuel into mechanical energy.