Is Higher Engine Thermal Efficiency Always Better?

[Kaleb]

Higher engine thermal efficiency is indeed better. Engine thermal efficiency refers to the ratio of heat converted into mechanical work to the total heat consumed by the engine. During normal operation, engines inevitably lose some power. Therefore, the higher the engine's working efficiency, the higher its thermal efficiency will be. This results in stronger vehicle power and lower fuel consumption. However, if an engine has high thermal efficiency but poor matching with the transmission, the drivetrain efficiency loss will be significant. In such cases, even with high engine thermal efficiency, the vehicle's fuel consumption won't decrease. When an engine and transmission are perfectly matched, drivetrain efficiency improves, naturally reducing fuel consumption. With advancements in engine technology, many automakers have improved their engines' thermal efficiency. Some brands have achieved 38% thermal efficiency, with some even exceeding 40%. The current highest thermal efficiency in the automotive industry is 45%, meaning only 45% of heat is utilized while the remaining 55% is wasted.