View Single Post
Old 08-12-2008, 12:38 AM   #8 (permalink)
Master EcoModder
Join Date: Jun 2008
Location: Earth
Posts: 5,209
Thanks: 225
Thanked 808 Times in 592 Posts
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.
  Reply With Quote