Aerochargers are better than (insert compressor)

[Greg Hermann]

At 10:04 PM 10/22/01, Matt Beaubien wrote:
>Greg,
>
>> Do you really think you will get optimum cruising fuel mileage if you are
>> exhausting a 200 plus HP engine through a 1.5" diameter single exhaust
>pipe
>> ??
>
>> Again, I will say that with the right controller, opening the wastegate at
>> light engine loads can help efficiency. Oddly enough, McInnes seems to
>> agree with me.
>
>It's been a little while since I've looked at a P-V and T-S diagram for an
>Otto cycle, but does it really matter much to the effciency of a throttled
>engine if you do it on the intake vs exaust side?  Say you created so much
>back pressure that you could run WOT at normal cruise--what would the
>efficiency be like?  I guess you have to take into account combustion
>effects (EGR etc) and not just the thermo diagrams.
>
>Matt.


Interesting question. Not claiming to have worked through the numbers, but
I think there's likely a big difference, and that throttling the exhaust
would be way less efficient. Exhaust backpressure creates a pumping loss,
just as an intake throttle does. But--it's also pretty easy to use a
restricted exhaust to cause an engine to absorb--instead of make--power.
Witness exhaust brakes.

Greg


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