he thermal efficiency of a turbofan engine is a measure of how effectively the engine converts the chemical energy in fuel into useful work, typically measured in terms of thrust. It is defined as the ratio of the useful work output (thrust) to the energy input from burning the fuel.
In a turbofan engine, a significant portion of the incoming air bypasses the combustion process and is directed around the engine core. This bypass air contributes to thrust without going through the high-temperature combustion process, which is a key feature that increases the overall efficiency of the engine.
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.