Which factors affect the thermal efficiency of a turbine engine?

The thermal efficiency of a turbine engine is primarily influenced by factors such as the turbine inlet temperature and the compression ratio. The turbine inlet temperature is crucial because higher temperatures generally lead to improved thermal efficiency, allowing the engine to extract more work from the combustion process.

Additionally, the compression ratio directly impacts how much air the engine can compress before combustion, with a higher compression ratio leading to better thermal efficiency. This is because higher pressure in the combustion chamber results in more complete combustion of the fuel, maximizing the energy output from the fuel consumed.

While ambient temperature and altitude can influence engine performance, they do not directly affect the inherent thermal efficiency as measured by the engine's design parameters. Likewise, aircraft speed and weight, while relevant to overall performance and operational efficiency, do not fundamentally alter the thermal efficiency attributes of the engine itself.

Thus, the primary factors recognized in optimizing a turbine engine's thermal efficiency are indeed turbine inlet temperature and compression ratio.