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----- Original Message -----
Sent: Thursday, September 18, 2003 12:39
AM
Subject: [FlyRotary] Re: Intake
questions
> >>> Also it turns out there is
no one magic runner length for the DIE effect and
> the length for this
effect depends not only on the rpm point you select for
> this
effect to occur but also on your particular engine specifications -
>
there that sounds mysterious enough, I think.<<<
>
>
> Lots of really great information showing up as a result of this
thread... this
> has to be one of the longest running discussions we've
enjoyed here. But
> that's not what I wanted to say....
>
> Considering how the DIE works (could the Dynamic Intake Effect possibly
have
> resulted in a worse acronym?) I'm really anxious to see the
results with the
> turbo. It seems to me that in a NA engine the
DIE is functioning in a low
> pressure system (at least until you get to
WOT and the MAP equals the baro
> setting). I'm wondering if the
positive pressure provided by the turbo's
> compressor is going to change
how it works. If we were to liken the intake
> system to an organ
pipe, as you lengthen the pipe its resonant frequency goes
> down (and is
the same reason you need to tune the runner length for maximum
> DIE at a
given RPM). At a fixed length that pipe will always sound the same
> note when a volume of air causes the column of air in the pipe to
resonate.
> If you increase the pressure, the pitch (frequency) of
the note remains the
> same but the volume increases. Given this
phenomenon, I wonder if the intake
> tubes set to the same length as
those that are providing an actual DIE in a NA
> application (at a given
RPM, of course) will show an increase in DIE with the
> positive turbo
pressure, or if the runners will need to be shortened
> (lengthened???)
to account for the DIE wave being slowed by the higher
> pressure intake
charge opposing it? OR..., it could be that the DIE is
> negligible
in the pressurized turboed system and the best results are to be
> gained
by the shortest runner length possible to minimize friction losses on
>
the incoming air stream. Lots to think about.........
>
>
<Marv>
>
> Hi Marv,
To be honest I have not even
thought about DIE with a Turbo, so am hesitant to make any pronouncements.
But, hey! my opinion is worth what you pay for it {:>). You will pay me
by the word won't you?
First, the DIE phenomena is unlike the "Organ
Pipe" or "Helmhotz Resonance" type theories, because it IS NOT DUE TO A
RESONANCE Phenomenon or the physics associate with it. All of these theories are
based on acoustical waves that result from a vibration (that is - a repeating
wave with a positive and negative pressure region associated with the
energy wave). There are some similarities like - they all are based on the
speed of sound of a wave of energy. However, the DIE effect is based
on finite-amplitude Waves which - while they are disturbances of the air -
have little else in common with the normal acoustical wave (we normally thing of
as "sound" ) in a pipe. A FAW for one thing only has either a positive or
a negative pressure zone associate with it - not both a the typical "sound wave"
does. Also, it is tens of thousands of time more powerful than even a 120db
sound wave. I am a novice in my understanding of FAW, but that much I understand
(and perhaps a bit more {:>))
The DIE effect is a result of some careful timing
considerations and the very powerful finite-amplitude waves (FAW) generated (in
any internal combustion engine - but perhaps even more intense in the
rotary). The wave travels at the speed of sound (1100-1350 ft/sec
depending on manifold air temp) when it slams into the relatively
stationary air that has accumulated in the chamber by the normal inflow of
air, the kinetic energy of the wave is transformed into increased manifold
pressure right at the intake port. Normally, after a piston/rotor has
reached Bottom Dead Center and started back on the compression stroke, the
intake is still open - or perhaps just starting to close. The
increasing pressure inside the chamber caused by the decreasing volume as the
piston/rotor comes in on the compression stroke forces a considerable amount
(20%? - it depends on a great number of variables) back out the closing, but
still open port. This is called "reversion" as I know you and many are
aware of. However, the increased pressure inside the chamber pushing out
this air/fuel mixture is sudden slammed by this high speed energy FAW wave
that transforms its energy into considerably more pressure in the intake near
the port. This higher pressure in the intake right next to the port then
overcomes the reversion pressure and probably even stuffs a bit more air/fuel
mixture into the chamber just before the port closes and goes on to the power
stroke.
Now having said all of that, it is my estimate that
the process will continue even with a turbocharger - I can't see any reason why
it shouldn't PROVIDED the intakes of the two rotors are
interconnected to provide a path. But, In most turbo
installations that is not necessarily the case, IF NOT
- NO DIE. But, if the interconnected path does exist in the turbo
installation, the effect probably still exists. In fact, in the NA 13B the
most powerful wave is created when the intake opens and the residue exhaust gas
(still left from the exhaust gas not expelled) burst from the opening intake
port. With a turbo charger, the exhaust back pressure is higher than an NA
engine. It seems reasonable to speculate that even more exhaust gas may be
retained by the rotor cycle as it come to opening the intake port. If so
it might follow that the wave that exits the opening port just might be even
more powerful, but would follow the same physics. The air temp in the
intake manifold will likely be higher than with an NA due to the heat caused by
the turbo compressor, so that means the wave would travel a bit faster. So
the exact length that is right for an NA engine might be off a bit for a turbo
engine. However, that would just mean that the effect would happen at a
(slightly?) different rpm than for the NA engine.
I am, however, not certain that all
of the design needs for turbo and an DIE effect are compatible.
For instance, what happens to the structure of this FAW wave when it hits the
intercooler?? Bet it doesn't stay the same {:>).
But remember this THE BASIC PERFORMANCE OF
YOUR INDUCTION SYSTEM IS STILL THE MOST IMPORTANT FACTOR. If it is not up
to snuff, then DIE effect does have much to enhance {:>).
I know there are folks getting ready to cut tubing
and would like to know all the answers now. But to be truthfully, it
really needs to be looked at on an individual basis because of the different
variables involved. Lets see if I can offer any
suggestions.
1. IF there is not a contiguous runner path
from the intake port of one rotor to the intake port of the second rotor in your
intake design - then forget DIE and press on. This might well be the case
in a turbocharger set up or even with a NA set up with Webber throttle
body. There must be a path for the wave to get from one intake port to the
intake of the other rotor
2. For the DIE effect there is a correlation
between DIE RPM point and runner length. BUT the length can be very
heavily influence by other variables. Selection of the DIE RPM point you
want sort of sets the basic environment that is fine tuned by other
variables. So what rpm point would you pick. Well, if you wanted the
additional enhancement at cruise, you would of course pick an higher rpm than if
you wanted the enhancement for take off and climb performance.
The DIE effect is to primarily enhance torque, but
as you know HP and torque are related.
Without stepping off this
tree limb, I would say don't cut your tubing too short. You can
always shorten it later.
3. Now this IS IMPORTANT,
the actually tube length you might use is only PART of the port to throttle body
distance. Since I don't know what configuration your manifold may have I
don't know how much of your port- port length will consist of
tubing as compared to perhaps using part of the stock lower manifold or
creating your own manifold casting etc. Just for your information the
intake ports are approx 2.5" inside block so you would need (at a minimum)
subtract 2 (for each port) x 2.5" = 5" from the port-port length because that is
inside the block and you couldn't change it if you wanted to {:>). Then
you have to consider the length inside your plenum (remember you have to connect
the runners from each port) that would have to be subtracted from the remaining
distance, then if you are using say the lower stock manifold or a after market
casting as part of your system, then the total path length it provides (remember
once for each port) would need to be considered BEFORE you could decide on the
tube runner length - EVEN if you already knew your DIE rpm and the total
port-port distant required.
4. So there, now you see why it somewhat
difficult for me to give any suggestion as to how long you should order your
tubing. If you have a stock NA (6 port) engine block you intend
to use I would say keep the individual runner length (port to throttle
body which is 1/2 the port-port distance) at least 30 inches (for the
moment) that is a port to port length of 60 inches. The DIE length for
aircraft use will undoubtedly be shorter and so your tube length (what ever part
of the total path length (60") that is) should not be any less than it takes to
ensure the port-TB length (1/2 Port-Port length) is 30". What ever you use
as a lower manifold (if not tubing) then will shorten the amount of tubing you
need, but if you created everything from block inlet to block inlet out of
tubing then I would say that you would be safe ordering at least 30" of tubing
for each 1/2 of the runner or the block to throttle body distance for a total of
60". You would probably need to do this both for the primary and
secondary paths This will leave you a tubing length that will probably
still be excessive once you fine tune it (at least you hope so) by cutting some
of it down, but easier than trying to add length.
4b. Another consideration is whether you are
going to maintain the primary and secondary runners separate. My analysis
shows there are some cases where this is probably wise to do and other cases
where it probably does not matter. Did I tell you I've spent months on
working this DIE analysis problem, while it is straight forward and is not
complex, its not necessarily simple due to the number of variables
involved.
5. If you are using a stock turbo block
without the turbo the tube length can be a bit shorter, but how much shorter
just depends. Follow same advice as for stock NA block.
6. If you have a none- stock block then it
just becomes too difficult to generalize without the specifics.
Best answer is to wait for the presentation -
because you just might decide that what I have to show you is horse hocky
{:>) or the bovine equivalent {:>)
Best Regards
Ed Anderson
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