Recovery of the heat is the way to improve these engines as that is where most of the power is, a Stirling engine connected to the exhaust could provide as much power as the internal combustion engine it is attached to doubling the power we get from the fuel but nobody makes them.
That remind me of vuel evaporator carburetor that utilize exhaust heat. Nobody can use it because they add additive in the fuel to make it jam the carburetor if you evaporate it....
Very true, the fuel here forms a varnish like substance after it evaporates, blocking jets and floats in the carb. Having said that so does the local gin, vodka and rhum, very worrying.