The thermal efficiency of an aircraft piston engine is a measure of how effectively the engine converts the chemical energy in fuel into useful work. Piston engines, also known as reciprocating engines, are commonly used in smaller aircraft. The thermal efficiency is defined as the ratio of the useful work output to the energy input from burning the fuel.
The thermal efficiency is expressed mathematically as:
where:
- is the thermal efficiency,
- is the thrust produced by the engine,
- is the jet velocity,
- ṁf is the mass flow rate of fuel,
- is the specific enthalpy of the fuel.