If a Stirling engine recovers energy from the exhaust gases(they have an high temperature) of an Otto engine then the total(Otto-Stirling) efficiency can be very good, I think it can be more high than a single Stirling engine.

Are you convinced?

you could obtain energy from the exhaust of one engine, however i doubt you could get a lot of energy, i dont know how overall efficient the pair of engines would be as you cannot harvest much power from the exhaust fumes.

 

whilst is may work i dont know about efficiency.

you could obtain energy from the exhaust of one engine' date=' however i doubt you could get a lot of energy, i dont know how overall efficient the pair of engines would be as you cannot harvest much power from the exhaust fumes.

 

whilst is may work i dont know about efficiency.[/quote']

 

The exaust gases have about 40% of the total thermal energy of gasoline and another 25% of this energy is in the radiator.

If a Stirling engine has an efficiency about 30% then you can add

another 20%(30% of (40+25)) at Otto efficiency: 25% + 20% = 45%.

But the only Stirling engine would have to be more efficient.