What is the term for the ratio of power produced by an engine to the power available in the fuel?

The term that describes the ratio of power produced by an engine to the power available in the fuel is known as thermal efficiency. This concept relates to how effectively an engine converts the heat energy from fuel into useful work or power. Thermal efficiency is calculated by taking the output power of the engine and dividing it by the energy input from the fuel, expressed as a percentage.

A high thermal efficiency indicates that a greater proportion of the energy content of the fuel is being converted into mechanical work, which is a desirable characteristic for engine performance. Understanding thermal efficiency is crucial for optimizing engine design and operation, as it directly affects fuel consumption and overall energy use.

The other options, while related to engine performance, refer to different measurements and concepts. Specific fuel consumption relates to fuel efficiency but does not describe the ratio of power directly. Indicated horsepower refers to the engine's power output before losses due to friction and exhaust, and volumetric efficiency deals with the effectiveness of an engine's intake system in filling the cylinders with air or air-fuel mixture. Each of these has distinct roles and definitions in the context of engine performance but does not define the power-to-fuel energy ratio that thermal efficiency does.