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.phpt=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 single plug 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

Ok Guys,
Some of the comments seem to be a little off base. The Smaller plugs should
require the same amount of energy to jump the GAP. The smaller loop-over
sidewire should allow the plug to be a bit closer to the combustion chamber.
That would make the gap a bit more accessible to the mixture, which MAY help
the combustion. The smaller recess should make for a tiny bit higher compression.

The best thing would be for NEW housings to be DESIGNED for the smaller plugs
which would allow the water jacket to be closer to the plug well and it might
help prevent cracking in that area under extreme power use. Mazda versions having
some small trouble cooling that area.I do like the idea of being able to run the
tiny coil-on-plug coils used on the modern motorcycles. Those coils are super light,
and usually are a ferrofluidic type which is great for low hesterisis. These coils
need to work on machines that have a 13,500 RPM redline on the street! They seem a
perfect choice for the multiple spark regimen of the rotary. Take a look at the
newest Honda or Yamaha 600's for good examples.
Bill Jepson

Bill you're exactly right. There is a small group of us that
are intending to mfg. a rotor housing using the small plugs
based on testing results we have accumulated.

Skip

This I got to see :)

Paul Lamar

Dave, Skip,

Thanks for the idea.I noticed that the inside of the trailing plug hole
had a little bevel on it where the factory no doubt took off the burr
after drilling. Wouldn't this small depression still allow some gas
to move from the compression stroke to the exhaust stroke

Bill

Thanks for the lead to the 10mm bike coil on plug info.About the
leading plugs.I was thinking about making a step shaped rectangular
stainless 303 insert with radius ends.It would have dualplug holes
and slip inside a milled out leading plug area of the housing, TIG
welded on the inside, and interface fit on the outside. Another plate
with gasket and plug holes is then bolted both to the outer housing as
well as the insert providing a water tight seal and mechanical strength
between the inner and outer housing. If the stainless insert had
grooves machined onto the outside where contacting coolant so much the
better for heat transfer.CHT sensor could be built into the insert as
well.Existing hole and boss is pretty muchmilled out with this
operation. Water passages should be a few millimeters wider on each side.

It would send you a Rhino file, except the by Windows based lap top just
died.

Doug in Japan

Doug,
I'll look forward to seeing the drawing when you getyou computer running again
Bill Jepson

By the way Doug, if you were able to weld in an insert you would probably need
to do some annealing of the welded area. This is a hot area which gets locally
much hotter than the area around the intake port. I am not sure why to run two
plugs in the leading position anyway,unless it is to ensure lighting a lean
mixture. I believe that running the multiple spark system Paul was talking about
would be more productive. Running a conformal insert with the small plug in it
in BOTH of the conventional locations makes more sense to me. I would like to
see a dyno chart report of improved function with dual plugs in the leading
position before I would do it.All of the information that I have seen in the
past shows that losing the leading plug was a 80% loss of power, and the loss of
the trailing plug caused a 20% power loss. The key here is that non-turbo at
least the trailing plugs are NEEDED and sagnifigant. Filling the area close to
the rotor and getting the plug as close as posible are the only idea that I
think works. The idea of the "side fire" modification allows you to put the
conventional plug closer to the combustion chamber safely, that is all it does.
Bill Jepson

Bill,

I guess the question is can you fly with twenty percent power if you
loose the leading

That's why the side by side spark plugs. The Wankel engine has dual
plugs but they feed the same hole. That's a good method as well.

Skip

As I recall people say loss of the top plug has little effect
on power. IMHO it was done for emissions primarily.

The dual side by side plugs have little effect on the BSFC
as those that have them show no advantage. On the other hand they are
either air cooled rotors or charged cooled rotor engines so it is not
a real back to back test.

Paul Lamar

Paul,
I would logically conclude the twined leading plugs are simply for standard
redundancy.BTW Mazda terms, lower plug LEADING, higher plug TRAILING. This was a
bit confusing to me at first. To answer Skip, I wouldn't want either plug failing
since you lose power either way.One answer for that is redundant COILS on the
same plug.You can get a'Y' to tee two coils into one plug. Electronics is the
likely failure, so I would feel safe with a single leading plug personally.I
will have 3 rotors though soI could probably limp home on2+20%. The single
rotor guys might have more to say about this. We aren't drag racers here
though. Once run for a while, say 20 hours, you have passed infant mortality
and if your temps are under control you will probably run for years. That is
why the FAA has the 40 hour fly off mark to begin with. Most of us won't even be
asking our engines to develop full automotive level HP! My 20B will be loafing to
produce the 250-260 HP max recommended for my RV-10. The twin turbo cosmo made 345
HP stock. I am not going out on a limb thinking that factors other than the
engine itself will be my likely failure modes. Paul has beating this into the
ground but it is true none the less, design your external systems carefully and
the rotary won't let you down.
Bill Jepson

Just forget leading and trailing. Use top or upper and bottom or lower
much less confusing.

Paul Lamar

Yeah you're right. It's wierd to say the bottom plugs fire
first (leading) then the top(trailing).

Skip


Bill you are absolutely right about  annealing the area around the weld
would be ideal though how  that would be done without warping the
housing? Pinpoint torch? Yes dual plugs  in the leading (bottom location
for all you guys that still believe that Australia is at the bottom of
the Earth)  are a necessity in my opinion for long flights over large
oceans.  This implies redundant ignition systems.   My engine will be
boosted and the trailing plug is not that important but I will probably
keep it in for testing purposes.  Multi firing plugs on any leading plug
is good in theory but would require extensive research to determine the
best plug to use.  As you well know, heat values of plugs is critical
for engine performance and multiple firing may change the heat index.
Yes I thought about Y-ing dual ignition systems into one plug but that
doesn't change the fact that  the Achillies tendon of the rotary
aviation engine is that it has only one leading plug.  If one goes out
in a 13B or even 20B the engine is probably going to be running so rough
that we would shut it down.

Dual plugs can also be fired in an alternating or staggered pattern.
Megasquirt has the code to do this with injectors, so it stands to
reason it can also be done with plugs.  The code is called Kurt staging.
Each plug can still fire at least once per cycle, which together
actually equates to a total of two firing event per cycle.  Following
your advice and experimenting with plugs found on high revving 16,000rpm
engines it would stand to reason that these plugs can be fired at twice
the rate that we need at max. power in the rotary. More at 6,000 rpm.
That gives us  4 -5 firing events per combustion cycle.

This is all fine and dandy on paper but it really takes a working
relationship with a spark plug manufacturer to come up with a plug that
can handle the heat of the rotary.  We are at the bleeding edge here.
The latest BOSCH plugs with the four prong cage around the central
emitter look to be the most promising technology for us. The spark has
four possible pathways. Plugs come pre gapped.

Perhaps like Skip mentioned two 10mm plugs angled into a central screw-in
insert might work. Actually I am loathe to do any welding on the rotor
housing if another alternative is out there.  Speaking of which. Anyone
know if a stainless boss is welded (in the manufacturing process)
outside the housing liner  and just inside the leading spark plug hole?
It doesn't appear to be aluminum. If so I wonder if it was annealed
before the liner was formed.

Doug in Japan.

If you fired the plug with 4 sparks .2 ms long 1 ms apart might be the same
effect on the plugs as one inductive spark 1 ms long.

I re read K.Y.'s book on the subject and there is little advantage to the
upper plug. What they published was BMEP data at only several lean mixture
settings. No BSFC data.

I think two lower plugs side by side are not worth it. Too risky! Could damage
the rotor housing but I have no objection to it if you are going
to carefully measure the BSFC change (if any) on a good dyno.

IMHO your better off spending your time and money on TC.
BTW how is that coming?

Paul Lamar

Paul,

Dual (lower) leading plugs have absolutely nothing to do with improving BSFC in
the engine.  Everything to do with saving my bacon if one plug or
ignition system goes south.  There is a reason that aircraft engines
have dual plugs and ignition systems you know.   Unfortunately when a
plug fouls on a four banger piston engine you know it immediately as the
engine gets very rough.  Not so on a rotary. Perhaps a maintenance alarm
pops up and you keep flying.  Land and clean or replace all plugs or remedy the
reason they were fouling.

Doug in Japan

Yes I can appreciate that.
One of the reasons is the A/C combustion chamber is five inches in diameter
or more and you get more power with two plugs.

What happens with the Mazda rotary is called sag. The engine looses a bit of power.
It still runs smooth. Probably enough to maintain altitude or extend the glide.

Just change out the plugs on a regular basis. 50 hours on 100LL and 100 hours
on autogas. If you have the right heat range complete plug failure is almost unknown.
CD systems will punch through fouled plugs.

Your flying a SeaWind. Just go IFR.


I Follow Rivers :)

Paul Lamar