Quote:
Originally Posted by Formula413
But isn't the power of the expansion used to move the piston in the firing stroke? How would just heat (and not pressure) turn the turbine?
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Jumping in here...
Yes, but it's a little more complicated a story. Heat forces the gas
to expand, the expanding gas' energy (mostly) stops pushing the piston down the bore once the exhaust valve opens, which happens near the middle of the ignition or power 'stroke', piston not yet to the the bottom (I think about mid-stroke). This residual positive pressure just gets vented to atmosphere via the tail pipe. A well designed turbo system takes advantage of that fact, and uses it to turn a compressor wheel. Why not turn a generator with that same shaft? At least, that's the idea.
Contrary to popular belief, zero restriction in the exhaust path (to atmophere) hurts the performance of most ICE's. Said another way,
some carefully controlled backpressure is actually a good thing for gasoline engine efficiency.