Multi Spark Plugs
Multi Spark Plugs
(OP)
What if any is the advantage of dual plugs in a combustion chamber?
Will it cause a flame front interferance?
If two plugs are better would three be ok?
I remember from my limited flying time that to check the mags you could switch back and forth and then to both and see the RPM change, but....
Will it cause a flame front interferance?
If two plugs are better would three be ok?
I remember from my limited flying time that to check the mags you could switch back and forth and then to both and see the RPM change, but....





RE: Multi Spark Plugs
Engines probably weren't very sophisticated in those days. We had just moved on from flat heads.
I have seen it as you have as pilots did their checks. I always wondered why they didn't just fly on both and start looking for plan B if one set went out.
But the experts will have to enlighten us. As Paul Harvey says, I'd like to know the 'rest of the story.'
rmw
RE: Multi Spark Plugs
RE: Multi Spark Plugs
RE: Multi Spark Plugs
With the advent of 10mm plugs and now .5mm dia Iridium pins it seems possible to put 4 or more plugs in a chamber.
RE: Multi Spark Plugs
RE: Multi Spark Plugs
I would think that the combustion process would determine whether more than one or two plugs is needed. There could also be an enormous packaging problem to get in more plugs along with the valves, ports, and head bolts in a small cylinder, and then get the cooling passages around them and finally have room for a mechanic to get to them.
RE: Multi Spark Plugs
I am sure they went through the same doubts when they asked how many valves are too many
RE: Multi Spark Plugs
One of the first engines I helped build was for a Cessna T-50 "Crane" in 1958. When we did the final runup on either engine, the rpm could not vary from left or right mag, or both begore delivery.
"Engines probably weren't very sophisticated in those days. We had just moved on from flat heads."
Actually, many engines in the beginning of the 20th century were OHV and OHC. David Dunbar Buick never built anything but OHV engines for the cars that bore his name, only the 29 Marquette used a flathead and it was really a "rebadged" Oldsmobile.
My dad retired from the fire dept.---the twinplug engines were also twin carbed, twin pumped, dual batts...you get the idea.
Keep in mind that "high octane" in 1930's was only 67 octane !!!! Oil changes were mandatory every 1000 miles, most cars did not have oil filters and many had no airfilter (valve jobs were common at 20k, too).
Lube jobs came EVERY oil change. Tires were good for, ummm, 12,000 miles if you were careful. AND...sparkplugs would last, maybe, 8 to 10 thousand miles at most! Factor in twinplugs and ??????
I learned to drive in a 1937 Nash Ambassador straight 8 with 16 plugs (8 on each side) and a giant 16 plug wire dual coil ign. I did not really appreaciate the significance then, it just looked cooooool!
So, twinplugs are used in modern engines to modify the flame propagation in a chamber that is a little too big(?), poorly engineered/designed (?)
to modify the exhaust emissions (?) What else?
Rod
RE: Multi Spark Plugs
Fire engines with gas engines had dual plugs and other duplicate backup systems. La France had a magnificent V12 that qualifies as overhead cam although it had a very tall/long combustion chamber. It was designed by Pierce for Pierce Arrow cars in the 1920s but they were built by Lycoming for American La France up to just about 1960, and yes, mine runs best when both ignitions are kicking in.
How many out there have heard about the PLASMA ignition? Hint- GM patented it in 175 for those curious enough to check it out. I told Jack Roush about it to squeak out more horsepower, but you don't see anyone running it in NASCAR (or anywhere else).
A guy in Ann Arbor, Michigan has probably the largest spark plug collection on earth (not just my opinion, Poplar Science's too). If my memory serves me correctly, he informed me the first tiny 10mm plugs showed up in the huge dirigible engines, and so Cadillac designed them into their large V12/16(?) engines to stay up with the latest technology.
I asked some engineers from Champion why on earth they put 3 or 4 ground prongs on aviation plugs when that would only promoted early fouling. Their response, "that's what the government specified!"
RE: Multi Spark Plugs
RE: Multi Spark Plugs
Googling that phrase produced a 1975 patent:
http://freepatentsonline.com/4041922.html
... which describes a 'corona discharge' prechamber ignition system assigned to Tokai TRW, which references two Kaehni patents issued in 1958.
The cool part, I thought at the time, was that there wasn't even a discrete timing mechanism; all the plugs fired all the time, in prechamgers, and the fuel in the cylinders ignited automatically, when it was ready. I recall no fuel supply in the prechambers; the engine had carburetors.
I speculate that the prechambers acted as plasma reservoirs, and ignition occured when the gas dynamics in the cylinder blew a little plasma out of the prechambers.
Mike Halloran
Pembroke Pines, FL, USA
RE: Multi Spark Plugs
Single rotor cap, but dual coils.
Ken
RE: Multi Spark Plugs
I studied that bucket T in Hot Rod magazine for hours as a kid to try to understand the principles. Looks like it could possibly lend itself to HCCI technology.
Back in the 60's, a guy & his son replaced the distributor in a 62 Chevy, 327 with 12.5:1 CR, with a direct injection pump and substituted injectors with NI-chrome wire for the spark plugs. The engine could burn anything at suerlean ratios. They had it at GM Tech Center- 650 HP at 62 MPG on coal slurry (virtually pure carbon)!
No one, not even Petersen Publishing (Hot Rod Magazine), nor EPA, paid any interest in it. The son wound up with a job at GM Tech Center. I offered $5000 for the car, but he said they were so letdown by the whole project, he'd leave it in the barn and will it to his buddy.
Jim Northrup, Sr.
RE: Multi Spark Plugs
Hydrae
RE: Multi Spark Plugs
I wonder if the continuous presence of plasma would erode the prechambers and the small passages to the cylinders.
Q: Does anybody know if the igniters in jet engines are fired continuously, or just when you're trying to start the damn thing?
Mike Halloran
Pembroke Pines, FL, USA
RE: Multi Spark Plugs
rmw
RE: Multi Spark Plugs
Franz
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RE: Multi Spark Plugs
the reason there are two plugs in aircraft engines is for redundancy and safety backup, but they run on independent magneto systems, something you don't need in cars even if you want to double plug a cylinder, if one mag fails then you have another one to run it on until you can land and get it fixed. But the design of the engine and the combustion chamber is made around the twin plugs, they didn't add the extra plug as and afterthought, that's why it becomes less efficient when running on just 1. There have been cases of both mags failing, especially when something breaks and overheats them.
I can think of at least one example of a 3-plug system. I read somewhere that mazda produces or produced a special racing version of the RENESIS rotary engine in the RX-8 with 3 plugs, the normal one having only 2
RE: Multi Spark Plugs
Regards
RE: Multi Spark Plugs
RE: Multi Spark Plugs
The Nissan engine with two spark plugs was called the NAPS Z engine. There are some SAE papers that show the spark plug arrangement, combustion chamber design, etc. See SAE 780006 and SAE 810010
Two spark plugs per cylinder make it easier to ignite dilute mixtures and helps to prevent misfires.
Two spark plugs per cylinder is pretty common: My friend had a 1996 ? FORD Mustang with a four banger that had two spark plugs per cylinder.
Mercedes had or has an engine with three valves and two spark plugs per cylinder
j2bprometheus
RE: Multi Spark Plugs
Porsche has been doing so since the fifties in its race engines and since 1989 in the two valve per cylinder 911 engine.
Benefits include: (Not in any order of importance).
A) More area under the torque curve. (Less negative torque due to necessary later spark timing). In a typical 911 engine, the spark lead must be reduced by approximately 10 crank shaft degrees with twin plugs compared to a single plug.
B) Reduced octane requirement. This is due to the fact that the characteristic known as detonation, requires time to manifest itself. A faster burn reduces the available time for detonation.
C) Fewer exhaust emissions. Read that; more efficient, more complete burn. Not to mention lower EGT.
D) Reduced specific fuel consumption.
E) Ability to run a higher compression ratio. (Go back to reduced octane requirement above).
There are other attributes to dual spark plugs in the above application but you should get the jist.
Of note is the fact that the Porsche 911 combustion chambers refered to above, are hemispherical and later, semi-hemispherical. In other words, these chambers are inefficient compared to other types of chamber designs and lend themselves to dual spark plugs quite nicely. A better way to word this is that this engine NEEDS dual spark plugs. At least the normally aspirated verion does. The Turbo charged engine has such an active chamber (swirl/tumble/etc.) that it does not respond to the twin plug deal as well.
Hope this is helpful.
RE: Multi Spark Plugs
I agree the multi plug could reduce octane requirements and also guessed; it would reduce lead time as the burn time is reduced. Thanks for the info on the torque curve that was not on my list.
RE: Multi Spark Plugs
How would a head design with 2 seperate combustion chambers fair? Plug in each chamber. 2 small flame fronts should be easier to control than one. Could be of huge benefit in a large bore engine, especially 2 stroke.
Ken
RE: Multi Spark Plugs
Is that in general for turbocharged, or is combustion chamber design still the big factor?
RE: Multi Spark Plugs
In my experience, an open or hemispherical combustion chamber is very efficient in a boosted application. The incoming charge being under pressure results in desirable chamber turbulence.
I cannot say that turbocharging "in general" results in a better burn. I can only comment on experience with hemispherical and semi-hemi designs. I will say that every engine we have tested that had lots of in-chamber turbulence, made more torque and had lower BSFC. This is after optomizing fuel and spark characteristics.
Sorry this post is not consistent with the original thread of dual spark plugs.
Will
RE: Multi Spark Plugs
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