Why is boundary layer turbulence GOOD, we havent gone over this topic in my
fluids class yet. Are you a ME, what school?
Javier
working on a ME degree @ASU
>Now that I've had time to think about it for a while, there's got to be
>something to it other than heat reduction. Each liter of air going through
>the intake spends a total of maybe a couple of hundredths of a second in
>the
>manifold. During this time, ideally, the airflow exhibits either laminar
>flow or laminar flow with a very small amount of boundary layer turbulence.
>(BTW this turbulence is GOOD and is the reason why you don't polish your
>intakes). So the volume of air that actually gets heated by the manifold
>is
>very small (because of aforementioned short time in manifold accompanied by
>low mixing rate in the gas charge). So if 1 percent of the intake charge
>gets heated by 100 degrees C, (which is 180 degrees F; quite a large
>increase) then the intake charge temperature goes up one degree C. This is
>insignificant compared with variations in ambient air temperature. Again,
>some real analysis combined with empirical data would tell the tale. I
>didn't see all that much difference in the dyno curves that couldn't be
>accounted for by different conditions on different days, or hood open vs.
>closed.
>
>As for what else could be happening, it's hard to say. Maybe some CFD work
>would be able to reveal that, but from what I've heard you rarely gain
>anything by moving the injector further upstream. But just because you've
>moved the manifold (on other cars) doesn't mean you have moved the
>injector.
>My Volvo had its injector ports in the cylinder head; you could move the
>manifold a foot away and it would make no difference aside from any
>velocity
>stack effect.
>
>Not saying I know the answer, but it's fun to think about. Oh by the way
>there's an online Otto cycle calculator at
>http://members.aol.com/engware/calc3.htm that you can use to see the
>effects
>of compression ratio, etc on efficiency. It's too bad you can't put in
>more
>parameters and get hp and torque vs rpm. That should be possible, even
>though it's not very accurate. At least you would know the BEST you could
>ever do.
>
>Dave
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