Francois,
I don't know if this helps, but I agree with you on the side
ports, I also
think they are restrictive and not just for the reason of surface
area,
That's why I like the P-Port 'direct inlet' - better breathing.
I'm not trying to convince you of anything - just a suggestion!
George (down under)
I agree with George on this Francois. You are building your own
rotor housings
and end housings why mess with side ports? Aluminum end housings
are much
easier to make if you don't have ports in them. Here is an Everett
Hatch engine
with aluminum end housings and P-ports. Super simple. 200 HP is
absolutely no problem
at all and the intake manifold is simpler and cheaper.
Francois is concerned about apex seal life with the PP. I'm not
sure why. Do you have any data in your archives about this Paul?
I'm okay with however Mistral goes, I'm just happy to have a solid
company building all aluminium engines. I'm especially happy that
he is going to sell us parts. Thank you Francois. Let us know
pricing and ordering details as soon as possible. I think you
should sell parts to the automotive aftermarket as well, it should
help increase your production volume. We can always develop an
aftermarket STC a Peripheral Port kit for the Mistral engines.
Hans Conser
I have no hard and fast data but I suspect the apex seals will run
cooler as they get a chance to be blasted by cool air. Side port seals
run 500 F. As far as the affects of the port opening itself... it is
no worse than a peripheral exhaust port.
So far Mistral has not committed to aluminum end housings. I could be
wrong. What I saw at OSH was a new rear housing cast in iron.
BTW how many people would be interested in an aluminum end housing if
they cost $1500 each?
$1000 each?
$500 each?
As far as design is concerned I still think the two piece is the way
to go. Cheaper, more reliable and over haul able as the hardened steel
insert can be replaced or ground and re nitrided. It needs to be
tried.
Paul Lamar
Mistral decided against PP for the following main reasons:
1. While a blast of cold intake mixture will cool the apex seals
indeed, we believe that thermal shock (the seal is being brushed by
hot exhaust gases, than by cold mixture a fraction of a second later)
is more detrimental to the seals' life than a more constant
temperature, even if it's a bit higher. This is an hypothesis of ours.
2. A peripheral port extends over about 80% of the width of the seal.
When the seal rides over the port, it is therefore supported only by a
few mm on each side. This induces a mechanical instability that wears
the seal, as well as the housing surface "downstream" from the port.
A peripheral exhaust port is already bad enough. A generally even
larger intake port is worse. Why do you think Mazda went to side
ports? Why do you think Mazda was able to increase substantially the
RPM redline on the Renesis? Because the seals ride on a perfectly
smooth surface (except, of course, the relatively tiny spark plug
holes).
Having said this, Mistral may do PP versions of its engines in the
future, especially for racing purposes where life expectations are
measured in hours, if not minutes.
Mistral's early side-housings are indeed cast-iron. However, Mistral
IS COMMITTED to Al side-housings. The development of long-lasting
(3,000 hours) Alside-housing is however FAR from evident. We'll go Al
if we are able to solve their existing short life-expectancy problems.
We believe it is a 12-month, several 100-thousand dollar development.
Francois
I know why Mazda went to side ports. It has to do with combustion
stability at low RPM low loads. The RX8 engine is impressive in its
ability to pull a loaded car away at idle.
All this was driven by car duty cycles where the car engine
spends a lot of time idling and putzing around town. Unburned
hydrocarbons and low power BSFC are the name of the game when it comes
to cars. I doubt the RX8 side port is any better than any other porting
method when it comes to high power BSFC. Tracy Crook confirmed
in-the-air-BSFC was no better than his old peripheral exhaust port
engine.
I have an extensive SAE paper on the side exhaust port subject written
by Mazda. SAE 950454 "The Characteristics of Fuel Consumption and
Exhaust Emissions of the Side Port Rotary Engine". It is kind of
incidental that the ports are 30% larger in area and the top RPM is up
allowing more HP at
the top end.
This heat balance chart is the driving force to improve the rotary BSFC
at low power. Note the car speed in this chart IS 80 Km per hour or
roughly 50 MPH. A car at this speed is lucky to need 25 HP.
Note the high percentage of chemical energy in the exhaust at
rich air fuel ratios.
The second chart is fuel consumption verses frequency of mis-fire at
idle.
Third chart is load verses combustion pressure fluctuations at 1500 RPM.
Fourth chart is load verses HC emissions at 1500 RPM.
In contrast to all this. At high RPM the rotary is close to a continuos
combustion engine. Much like a turbine.
We would be better off injecting compressed air into the squish area on
a continuos basis at high power. More on that soon.
P-port engines don't wear any faster than side port engines.
Mazda examined the wear of the Le Mans p-port engine after the race and
the wear was within manufacturing tolerance. In other words they were
unable to detect any wear. This engine spent a large percentage of its
time at 8500 RPM full power for 24 hours. Many p-port engines
were raced in the late 70's and 80's. Many raced for ten or twenty races
without being overhauled while most piston engines were overhauled after
every race. There is absolutely no evidence what so ever that p port
engines wear any faster than any other kind of rotary engine.
If you are serious about long life and you are charging $20,000 for an
NA aircraft engine it better have ceramic apex seals. The wear on these
when used in p port or side port engines is near impossible to measure.
Combination steel and aluminum end housings will last just as long as
the stock combination steel and aluminum rotor housing used by Mazda. It
is just a matter of investment to copy the technique Mazda uses for
manufacturing rotor housings. The thin raw steel liner is prepared by
passing it through a machine that forms ribs on one side of the metal.
It is then rolled up and seam welded to form the trochode(s?) shape. It
is placed in the mold and the aluminum cast around it. It is then
accurately ground to final shape. (I am the only outsider to ever see
inside the Mazda rotary engine factory :))
The foundry that made my intake manifolds here in So Cal specializes in
casting steel inserts into aluminum castings. No big deal. They have
done thousands over the years. Even I could afford to have it done if I
could also afford to make the dies that form the ribs in the steel.
Also the casting patterns and core boxes for the end housings are also
expensive but Francois has already paid for those.
Francois, What are you using for wear coatings on your rotor housing?
Paul Lamar
Matt Prather wrote:
Francois, this is a fascinating discussion... I feel we are very lucky to
have you writing on this exchange (you too Paul :)).
Matt-
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