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Old 08-12-2008, 12:38 AM   #8 (permalink)
jamesqf
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Quote:
Originally Posted by c-serpent View Post
...but then why not just do a turbocharger?
Because the turbocharger only uses a small fraction of the energy in the exhaust gas, maybe?

As for the engine doing more work, it doesn't work that way. Just think about it: suppose you hold the amount of fuel going in constant, then you have X hp out of the engine. Put in the correctly-sized turbo-generator, and the engine produces X hp minus small fraction Y because of back pressure, while the turbo generates several times Y.

This isn't a completely new idea: it was used on some WWII aircraft engines: Turbo-compound engine - Wikipedia, the free encyclopedia It's really a bit of a dead end, though, as that article points out. Cars have used IC engines not because they're efficient (they're not), but because they have the torque & acceleration that a car needs. If you have a Volt-like hybrid, where the wheels are driven by electric motors while the engine turns a generator, you can dump the IC engine and use a much more efficient turbine or Stirling engine. This would at least double the mpg of an IC engine, even before you figure gains from regen or grid charging the battery.
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