I apologize if it's the wrong forum for this Is it possible to efficiently construct an internal combustion engine and while it's running to use its waste heat as the external combustion of a (smaller) Stirling engine? If so, the Stirling engine could power a generator that will essentially replace MG1 in a Prius. However, unlike MG1 in a Prius, this generator will only charge the batteries or send electricity directly to the other motor/generator (the equivalent of MG2 in a Prius). The generator connected to the Stirling will not be mechanically linked to the Power-Split-Device. Intuitively, this should reduce the resistance of the drivetrain while moving because then it's not necessary to match the revolution of two electric motors to the revolution of the ICE. And most importantly, power that is produced from waste heat is, dare I say, FREE?
What you are describing is called a combined cycle plant. This sort of thing was commonly done at the peak of steam engine design, where double or even triple expansion engines used a final Stirling Cycle stage. Now it is mostly used at fixed plants, where size and weight are not important. For an automobile, size, weight, and cost are all significant factors, and work against a combined cycle power plant. It could be built, but it's not likely to be built, unless these factors decrease significantly. Tom
A less extreme idea along this line would be to use excess heat produced by combustion to fuel a Servel-type refrigeration system. This could convert engine heat to either cabin or battery cooling when the need for each is greatest.
MG1 is essential to the HSD system, it cannot be removed and still have HSD function efficiently. Your Sterling cycle engine should drive an additional generator, which we could label MG3. Have you found a Sterling design compact and light enough to be useful in a motor car? Remember also that the Atkinson cycle engine in a hybrid, with its large expansion ratio, leaves less exhaust heat than does a traditional Otto cycle engine.
What you are really looking for is a thermoelectric generator: [ame=http://en.wikipedia.org/wiki/Thermoelectric_effect]Thermoelectric effect - Wikipedia, the free encyclopedia[/ame] Ferrotec Thermoelectric Products This generates electricity from the temperature differential. It's much smaller but the question would be the price vs. electricity generated.
