Date: Sat, 30 Jan 1999 16:33:19 -0800
From: Paul <rotaryeng@earthlink.net>
To: z <rotaryeng@earthlink.net>
Subject: Dynamic Chamber Intake manifolds
Tracy Crook wrote:
Paul Yaw wrote:
snip...............lots.... see previous message from Paul Yaw.
I would like to point out that with a proper exhaust system, the
second
pressure wave which is initiated by exhaust back pressure will not
exist, and so the remaining wave will need to be delayed by 180
degrees
if it is to arrive at the intake port closing of rotor #2. This
(at
least on paper) corresponds to a runner length of 32.2 inches for
maximum effect at 6000 rpm. I should also point out that a high
pressure wave will have the greatest effect on volumetric
efficiency if
it arrives right before intake port closing.
Interesting number. It seems very close to one that I have heard
mentioned on this newsletter before.
Paul Yaw
Excellent analysis of the DC manifold Paul Yaw, best I've seen. Your
numbers
for the runner lengths look right to me. The full picture of how
this
works is starting to come into focus here.
Since it is hard to fabricate an exhaust system that is both tuned
for best
power AND quiet in an aircraft installation (here we go, another long
debate
:-) ), I think we are working with the exhaust pressure pulse, so the
shorter runner length would apply.
Hey! See my tuned muffler on the web site. Its not that hard!
Also don't get too fond of this exhaust pressure wave theory without
actually
looking at an open engine with the rotor in the housing. Not much at
all will make it through there from pheriperal exhaust to side intake.
It should also be remembered that the length in Paul Yaw's message
is
the TOTAL length of runner between rotor 1 and 2. That means the
runner
length from each port to the DC would only be about NINE inches long.
And
remember that there are a few inches of runner length between the port
on
the side of the engine block to the actual port opening to the rotor
chamber. The length of the DC itself also counts in this setup.
Considering all this, I'm beginning to think my existing manifold
runners
are TOO LONG! :-) I can't wait to see how that little composite
manifold
on my test stand will work.
On the topic of Everett's manifold, his was a classic tuned pipe, not
a DC
design. According to him, 4 tubes (even of the perfect length) going
to a
side-port engine did not work well on the dyno for a 6000 rpm design.
His
explanation was that the velocity was too low when split between the
two
pipes (per rotor). This was his primary reason for going to
peripheral
ports.
Tracy Crook rws@altavista.net
I don't buy it!
Velocity of flow or velocity of the pulse? If the air density is the
same and the engine is using a given amount of air (same HP) the
velocity
of the flow in the pipes is inversly proportional to total pipe area
except for skin friction drag effects chokeing off the flow in two
pipes.
Use two tapered intake pipes near the ports and make them bigger.
It does not matter if the average flow is one mile an hour or 200 MPH
the pressure pulse will still propagate at the speed of sound.
That's why big pipes are better and big ports are better.
Look at the size of the sewer pipes Mazda used on the
Le Mans engine.
Everett could be wrong! You guys need to read Taylor.
Everett used to carry his around like a bible. We would go out to
lunch and he would bring it with him. :-)
The enclosed chart is from Taylor Volume I page 175. machindx.jpg
"The Internal Combustion Engine in Theory and Practice."
Volume 1: Thermodynamics, Fluid Flow, Performance. Second Edition
Revised.
Volume 2: Combustion, Fuels, Materials, Design. Revised. Charles
Fayette Taylor. The MIT Press Cambridge Massachusetts, and London
England.
Will you guys stop screwing around and get some of those
manifolds on the dyno? :-) :-)
Paul Lamar
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