The thermal efficiency of a turboprop engine is a measure of how effectively the engine converts the chemical energy in fuel into useful work, typically measured in terms of the propeller thrust and/or shaft power. The thermal efficiency is defined as the ratio of the useful work output to the energy input from burning the fuel.
Turboprop engines combine a gas turbine core (similar to that of a turbojet or turbofan) with a propeller-driven system. The thermal efficiency of a turboprop engine takes into account the work done by the propeller in addition to any jet thrust generated by the exhaust gases. The propeller contributes to the overall thrust and is driven by the shaft power extracted from the gas turbine core.
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.