a throttleless premixed-charge engine is the extreme evolution of the Warm Air Intake concept:
it's an experimental motor (based on a production automotive 4-cylinder) which is not restricted by a butterfly valve, but which is controlled by adjusting the air density (through heating) and fuel mix:
- up to 16% more efficient compared to the same engine operated using conventional throttle control at same power and engine speed) due to the absence of throttling losses
holy crap. It's stuff like this that give me hope for the future. I'm willing to bet that this combined with the exhaust turbo-like alternator would provide a huge mpg savings. The best part about these technologies is that they can be retrofitted to existing engines.
Diesel engines are the original throttleless engines.
Try looking at the Fairbanks-Morse website for a really interesting throttleless natural gas engine. Their opposed piston diesel/natural gas engine has a thermodynamic efficiency of about 40%. This is significantly better than automotive diesels, which are about 32-34% efficient, and enormously better than automotive gas engines which are about 25% efficient.
Because of their relatvely small size, (relatively) light weight and high efficiency, Fairbanks-Morse opposed piston diesel engines powered US submarines until nuclear power came along in the '60s.
Five such engines are used to power flood control pumps at the Charles River dam in Boston. It's a public facility run by the Metropolitan District Commisssion. Maybe they will give you a tour.
Poor US people are still doomed to thinking diesels are dirty, when in fact they are now cleaner than gas, which is why most new cars in europe are diesel and get much better mileage. Gas is crap. And diesel cars can be run on veggie oil, so screw gas I say.