Ara, the airflow through an internal combustion engine is NOT
unidirectional, despite your wish that it would be. Various forms of valve arrangements *attempt*, but fail to completely prevent *reverse flow*. Technology involving computer controlled exhaust throttling valves has been available from Japan for nearly fifteen years. One company produced it under two different names. PowerValve is one name and ExUp is the other one. I have a vehicle equipped with ExUp in my garage right now. The exhaust throttling valve never
completely closes, as in your "potato" analogy. It is about one-
third open at idle, and, as the computer senses rpm increase,
it opens fully. The exhaust throttling valve increases the low-end
torque of the engine, and the gas mileage is increased from 38
miles per gallon to 45 miles per gallon. The exhaust throttling valve
helps to eliminate the flat spot in the torque curve which is caused
by *reverse flow* at about 5500 to 7000 rpm. I am sure that if this company ever went to fuel injection, the mileage would get into the middle 50's, because *reverse flow* through the throttle bodies would
have no effect. That's right, Ara, I said *reverse flow*. In some engine
designs, air passes through the carburetors up to *four* times!
And, on each pass, more fuel is added to the mixture, because
the carburetor is a dumb device that doesn't know about *reverse
flow*. In fact, with the air cleaners off the carbureted engine, a
*fog* of fuel air mixture could be seen *outside* the carburetors
in one particular design. The manufacturers eventually added a
one-way valve between the carburetors and the cylinders, but
it took ten years to do it, because the public wasn't complaining
about fuel mileage, they were complaining about low-end throttle
response. And it took another ten years to get the exhaust throttling
valve technology onto the street. It had been thoroughly proven
off-road by this company which does research and development
for Toyota, but which is also widely known for its musical instruments.
And every one of its competitors has adopted an exhaust throttling
system for its off-road vehicles. But, then again, I don't know a
thing about engines... |
