Steve,
As Paul and many others among our group have said, many thanks for
sharing
your wealth of experience with rotary installations. Can't beat hands on
experience. Getting back to the CDI vs Conventional ignition, the rotary
is a unique case because the spark plugs can't protrude into the chamber
at all. Since the sliding seals prevent that I would think that a plug
that presented the electrodes as close as possible would be best. I read
that VW was experimenting with a no-side-wire plug and apointedprojection
on the piston to fire to. I don't know if they ever used it inproduction.
The spark actually jumped to the piston. I thought that this typeofsystem
would be perfect for the rotary. The plug could be closer to the rotor
without a side wire and the long spark would be perfect to ignite the
lean mixture. Having the plug closer would even bump the compression a
little. Just thinking out loud but it seems like a possibility.
Bill Jepson

We always removed the spark plug washer to move the plug closer.
Works great. There are washers available from Mazda.

Skip

Skip did you use no washer or the substitute washer from Mazda Any
measurable difference in performance or other, such as different carbon
patterns on rotor at disassembly

Steve Beckham

Steve, We took the washer off. It was a drag race application. The gain
was only measurable at the track clocks. We thought we had a secret
performance gain, then we found that Mazda Speed offers washers to
move the plug in or out.

Skip

Steve, I'd like to say some more about the spark plug issue. The
sparkplug
washer trick did not have any effect on charged cooled rotaries. In fact
is was a negative effect. Don't know why that was. What did work is we
changed from a 14mm spark plug to a 10mm spark plug and gained some real
hp and torque. Ten to twelve hp on a single rotor. There is a serious
leak when the apex seal goes over the hole or any hole in the
rotorhousing.
So the smaller the hole the better. I'd like to reduce the Mazda. I don't
know why they don't. Just about every mfg has gone to a smaller
sparkplug.

Skip
-

That is only for the trailing plug Skip.
There must have been something else going on with the Rotamax.

Paul Lamar

Thanks Skip...no doubt about the factor of the apex seal going by the
spark
plugs.I remember at some point one of the Mazda factory guys in the early
1990's telling us they dealt with this factor when they did the three
sparkplug modification for the four rotor LeMans project.They were using
castings with an additional sparkplug above the two original
sparkplugs to
address the highly quenched trailing end and its poor flame propagation,
they made the plug hole as small as possible.It demonstrably worked to
address fuel consumption byburning some of the fuel that was before
simply
going out the exhaust pipe.

But having said that, the leakage was clearly
evident because while it actually improved fuel consumption, the
volumetric
efficiency of the engine dropped according to the Mazda folks.About the
simplest way they addressed the high-to-low pressure area flow was to
keep
the plug hole as small as possible.For our application of the engine to
sustained high power settings involved in aircraft use, at this point in
development and using proven technologies, it seems the three sparkplug
approach with this small hole would work well to substantively address
the
issue of this highly inefficient and quenched area in the combustion
chamber.

But Mazda is driven by the automotive production market and it is
clear they ran the numbers and more cost-effective to develop the two
sparkplug side port RX-8 to reduce the overlap and improve BSFC for road
cars.Just wonder whether deep in the bowels of Hiroshima whether a group
of people have, or arepresently working to save this little engine by
experimenting with more than one option, includingUncle Paul's turbo
compound ideas.If not, it is because their hands are tied financially by
short term cash flow and profitabilitythreatening car companies.The
Mazda organization has some amazing, smart folks who remain inspired by
their rotary "father", then later Mazda Chairman Yamamoto.It seems they
must have already, or are currently exploring the TC option to see
what it
could hold for this little engine by putting to work that unusually high
amount of energy going out the exhaust pipe.

Meanwhile, absent any major
changes in design, we know a three sparkplug approach works to improve
the
burn and improve fuel mileage.Yasuo Tatsutomi told Yoshinori Honiden they
had to reduce fuel consumption 10-15% to win LeMans with an rpm band that
could range from 6,000-9,000.To do that with a standard, homogenous
charge
engine is like climbing Mt. Everest. They simply could not have done it
without those rotor housings.Even with them, the LeMans drivers had
strict
orders from Yoshinori Honiden to lift and early/coast at the end of the
straight and soft pedal through the corners. The primary goal was fuel
savings but it was also easier on the engine heat flux.In this respect
they even went from black to silver paint on the upper engine cowlto
address temperature issues.

The previous year the ceramic exfoliated inside
the engines. Aircraft race duty cyle is harder--no lifting at the end of
the straight stretch and going into corners-- and we are attempting to do
that using what are basically warmed over, off-the-shelf production parts
for grocery getters.That is a serious challange no matter how we slice
it.
But in the words of Nobuhiro Yamamoto (he headed up the third gen RX-7
engine development),after the LeMans effort,"We can no longer say we
share major components between the production and racing rotaries.But we
are still a very close bunch--the rotary people!"A rotary brother indeed.

-
Steve Beckham

Steve,
I seems to me that the idea to use a small plug would be very"doable".
Filling the spark plug hole and using the 10mm plugs to keep everything
tighter to the chamber seems like a good idea. Motorcycles have been
using the "little" spark plugs for years sothey are available. Using
10mm plugs would also be a better way to add the far trailing plug.
I think using the standard housings and trying to do the milled side
plates, (all steel nitrided),and staying with all p-port will get us
closest to the proper aircraft configuration.
Bill Jepson

I understand that a flush (or nearly so) spark plug was tried but that
the
problem with it was carbon trace arcing/shorting.Could a plug be designed
that was truly flush with the housing surface which was kept clean by the
passage of the apex seal - eliminating any carbon buildup?The
sealing/insulating material would have to be designed to be cut/eroded by
the apex seal, and not cause the seal any damage.

Matt-

And tolerate super high temperatures :)

Paul Lamar

Paul,

Sorry. Mouseititis again. It appears NKH is working on a 10 mm size
spark plug for the rotary though they wouldn't commit on when it would
be available for the racing community. They did show me long narrow ten
mm plugs but they where the bent tang type normally found in piston
engines. A good guess is they made some concentric iridium tip types
for Mazda engine research use only. Speaking of which. If you follow
the course of Mazda engine development you can understand why they are
playing with dual fuels, specifically the addition of hydrogen. The
all-hydrogen engine was for testing and probably good PR. Hydrogen or
better yet, on board generated H00H makes sense if injected in small
amounts (less than 0.4% by weight) right after gasoline is injected and
the intake port closes. This would imply the hydrogen fuel is injected
at the top of the housing. Looking at the 16X housing pictures you can
see this is so. The H2 burn rate is so rapid that it solves a lot of
problems associated with trailing plugs and multi sparks. The hydrogen
or Hydroxl gas fuel first ignites and this in turn ignites the fuel
droplets.

My interest in smaller footprint dual plugs was in trying to make the
dual plug insert a bit narrower to minimize both the liner welded area
and inner water passage restriction. Closer together also brings both
sparks into the central rotor depression area instead of near the rotor
edge. Having the sparks nearby in my thinking would minimize an
asymmetrical pressure on the rotor face in case one ignition system
failed.

Dual fuels adds complexity, as do sequence fired capacitors without a
doubt, but a loss of the hydrogen injection would not be a show stopper.

Doug in Japan

Some of this is discussed in Kenichi Yamamoto's Rotary Engine Bible-1981.
http://www.wankel.net/~krwright/cars/rx7/manuals.html, page 50-ish

While people are talking plugs.
Has anyone experimented with single pronged side fire plugs or RX8 fine
wire leading plugs VS the older plug styles?

I have read of folks getting better mileage with side fire plugs:
http://www.mazspeed.com/sidefire.htm
http://www.rx7club.com/showthread.php?t=656700

I have wondered if adding flame front channels from the rotor recess
towards the apexes might help with the squish areas, possibly with
trailing negative split.

Has anyone measured the difference in fuel economy with/without wasted
spark on the leading plugs?
Leading to getting rid of the trailing plug entirely, in favor of twin
leading plugs (at least move the trailing closer to the leading).

Cheers
Cary


yes I have.

Skip

Well Skip can you tell us what you found? :)

Paul Lamar

Cary,

Thanks for posting those threads from the RX forum.I plan to go back to
NGK now and see how many models they have out on their new long skinny
10mm plugs. I am ready to cut a dual plug insert next weekon the
test configuration housing so a smaller footprint would make me happy.
Yes modifyingplugs to side fire may seem to be a hazzle but if they
last much longer and more importantly are more efficient then that is a
acceptable trade-off.Question remains on how much energy it would
takes to fire the smaller plugs. I guessthis means we would also
have to search for different coils to power them.

Doug in Japan

Hi Doug;
The 10mm plugs sound like the way to go.
I'll probably try a set of the side fire plugs in the car shortly.  I'll
try to drive
like grandma to pseudo scientifically measure it :)
I expect the side-fire plugs and close plug location will help most with
low
power and leaned out economy modes.  The closer proximity of the plug
and reduced interference of the single electrode should help with
ignitability.
A larger .055"+? gap and stronger spark would probably help as well.

I'm curious, what plug configuration /location have you selected for
testing?

http://www.wankel.net/~krwright/cars/rx7/manuals.html, page 53
Figure 4.54, always struck me as an interesting chart.  If I interpret
it correctly,
a singleplug results in slower, more complete burning and gets slightly
less HP.
hmmm
Not sure if there is an optimal mechanical advantage factor going on based
on the flame front - need to look at the rotor/eshaft location.
It also me strikes me as a quick fix for passing emissions...
Cheers
Cary