According to the internet, an internal combustion engine is powered by the pressure differential when the fuel expands into gas and has a maximum thermal efficiency of 50%. And a steam turbine is powered by the temperature differential when the fuel releases its chemical energy as heat and has a maximum thermal efficiency of 90%.
What would happen if you sunk the heat from the internal combustion engine into the boiler of the steam turbine, instead of just venting it into the atmosphere as a waste product? I'm guessing it wouldn't have a thermal efficiency of 140% but WHY wouldn't it? Does harnessing the gas expansion reduce the amount of waste heat? According to which physical laws would THAT happen?
Why isn't a combined cycle power plant 140% efficient?