|
Does he really have DIE? - No, its not some new
virus or social disease, it's associated with performance and the rotary engine.
In fact a presentation on DIE will be presented at the Shady Bend Rotary flyin
in October (see outline at end of message)
As those of you who may also be on the rotaryengine
list know, Paul and I have gone around a bit about whether or not my 48" (port -
port) intake ever provide the dynamic intake effect (DIE) (self supercharging of
the rotary engine) at a high enough rpm to be of use for aircraft
application.
Paul maintains (correctly, I might add) that with
48" intake manifold (length on the 1988 NA 13B) the Mazda data
(rpm/torque/hp curves) clearly shows that the DIE effect occurs around 3500 rpm
for the pre 1990 NA 13B. That much was clearly evident in the Mazda
data. But, I knew something was causing my engine to go from a static rpm
of 5200 nominal on a 70F + day to 5800 on a cold day. At first I convinced
myself that the lower density altitude due to the cold was causing a small HP
increase enough to put my prop in the "stalled" condition. But, I finally
figured out that was not the case. Paul suggested the Helmholtz Resonance
effect, but after working on that approach for a while, I decided that did not
provide the answer. So I turned back to the DIE.
Paul was kind enough to provide me with some of his
SAE Mazda Papers. I am not certain whether to keep me busy and from
pestering him or to educate me (I chose to think the latter). After we
exchanged a few more e mails, he made it fairly clear, as
only Paul can do, that as far as he was concerned the topic was closed and
that I should radically shorten the planned intake for my 3rd intake (the
one with the plastic plenum). So I knew it
was time to drop the debate with Paul.
In any case amongst the SAE papers that
Paul was a gent to provide, I finally realized I was looking at the
KEY bit of information. In other words, I found (at long last) the
answer after much head scratching, skull work and spread sheet
doodling.
The answer is that Paul IS
correct IF you have a STOCK NA 13B block - with the STOCK Intake manifold and operating under stock
conditions. Otherwise, all bets are off where the DIE rpm point may occur
at.
It turns out, I WAS
also correct. I was indeed getting a increase in power from the DIE
in the mid 5000 rpm range with a 48" Length
manifold but did not understand how that was possible at the
time.
Let me make it clear that when I say a manifold
length of 48" that is the total distance from the intake port of the front rotor
through the intake manifold past the throttle body to the intake port of the
rear rotor. In other words, it includes the 2.5" inches distance into the
block to the port opening as well. So approx 1/2 of that distance (minus
the internal block distance) is my runner length.
Anyhow, Once I had completed the analysis a number
of things I had noticed with my engine became clear. My analysis will show
how that is possible - no not possible - ordained (not in the religious sense)
that I would get DIE at a mid 5000 rpm with a 48" length. Paul's
advice to make my intake shorter was incorrect
but only because MY engine is NOT
STOCK. And to be fair, neither of use really understood the effect
of the variables involved at that point. So Paul was relying on the Mazda
data he had which ,of course, is for a stock engine.
The 3rd manifold ended up too short as I
completed it before I completed my analysis, darn!. However, its
short length was not a result of following Paul's advice. I ran
into a physical configuration constraint with the size of the new plastic
plenum that forced me to make the manifold length around 42".
And no, no DIE effect in my operating rpm range - it turns out the DIE for this
manifold is above my normal RPM operating range
for MY ENGINE.
It took me over a month of sitting down
and working out the real details (never before revealed {:>)) of the
variables involved and the relationships among them (in other words equations
that could be used).
RPM and Manifold Length are
only two of the variables that I have identified that have a
significant effect at what RPM the DIE effect occurs. actually there are over
twice as many. If any of these variables are not operating as designed for
on a STOCK NA 13B with the stock intake manifold, then the DIE will not occur at
the Mazda designed RPM point - BUT it can still occur, the question is at
what new point.
I have a presentation that I am whittling down from
its current 60 VuGraphs (arrggg!) to be presented at the Shady Bend Flyin in
late October. I will not reveal the findings before then, but if your are
interested the outline of the briefing is:
Dynamic Intake Effect -
The Concept (This is just a few introductory Vugraphs to
reacquaint or introduce the newcomer to the dynamic intake effect concept that
Mazda used)
Dynamic Intake Effect -
The Analysis and Synthesis (This is guts of the presentation
taking you through the analysis, the identification of the variables, and their
influence on the DIE and showing the relationships of these variables (no math
higher than simple algebra) with a number of charts and graphs showing this
stuff - currently 31 vgs)
Dynamic Intake Effect -
The Comparison with Ground Truth (The dicey part {:>) - where
I show how well the numbers that my equations come up with stack up against what
hard facts we know about the effect - from Mazda itself. I create some
parametric curves based on the equations derived that correlate manifold
length with RPM for the DIE effect holding the other terms constant, its
really pretty straight forward once you see it (says I) - currently 29
vgs)
I think you will find it interesting (if I don't
put you to sleep).
Hope to see you there. Check Tracy and Laura's
website for details of the flyin. Please let Laura know if you plan on
coming.
Best Regards
|