The thermal efficiency of a high bypass ratio (HBR) turbofan engine is a measure of how effectively the engine converts the chemical energy in fuel into useful work, primarily in the form of thrust. High bypass ratio turbofan engines are designed with a significant portion of the incoming air bypassing the combustion process, resulting in increased propulsive efficiency and fuel efficiency. 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.