What is indicated thermal efficiency?

Indicated thermal efficiency is a measure of the effectiveness of an engine in converting the heat energy produced during combustion into useful work. It is calculated by comparing the indicated power (the power developed in the engine's cylinders) to the energy input from the fuel. This efficiency reflects the engine's performance under ideal conditions, not accounting for losses due to friction, heat dissipation, or other factors. In essence, it provides insight into how well an engine utilizes the energy from fuel.