Does using dual spark plugs per cylinder make any difference?

[HyperTechno]

There is this bike manufactured in India with a 180CC single cylinder petrol engine with Twin Spark plugs. They highly market their "twin spark technology". Well according to my knowledge, I don't think that will make much difference in performance and efficiency. What do you think? Is this just a marketing gimmick or a purposeful technology? Thank you.

 

[FactChecker]

A single spark plug may not get all the fuel burned fast enough to get all the power and efficiency before the exhaust port opens. A lot depends on how the fuel swirls in the combustion chamber as it burns. Two spark plugs can help that. So can multiple sparks from one plug or careful design of the cylinder head and ports to get a better burn. Needing a second spark plug is not common these days even in very powerful and efficient engines, so I am not sure that it is something to brag about. But the way they have designed that particular engine, it might work better than a single plug.

 

[Baluncore]

The speed of flame propagation can limit the maximum speed of an engine. For economic efficiency and environmental requirements, a two-stroke engine with one big cylinder may gain a real advantage in having two spark plugs to enable higher RPM.

 

[Ranger Mike]

Depending on the combustion chamber design and maximum RPM, dual plugs will help relative to performance and efficiency. The difference is very little and extra cost is probably not worth it.

 

[Nidum]

Some of the Bristol series of radial aero engines had two spark plugs per cylinder and two independent ignition systems . This was primarily for reliability rather than to enhance performance .

One of the main causes of in flight failure of engines in the earlier days was ignition system problems .

 

[HyperTechno]

The speed of flame propagation can limit the maximum speed of an engine. For economic efficiency and environmental requirements, a two-stroke engine with one big cylinder may gain a real advantage in having two spark plugs to enable higher RPM.

That's a 4 strock engine.

 

[HyperTechno]

Some of the Bristol series of radial aero engines had two spark plugs per cylinder and two independent ignition systems . This was primarily for reliability rather than to enhance performance .

One of the main causes of in flight failure of engines in the earlier days was ignition system problems .

But this is a motor bike and not a racing bike, one designed for regular use. The engine is just , 180CC.so...

 

[Averagesupernova]

The Mazda RX7 (wankel) used 2 plugs per rotor for years. While it is true that dual plugs and ignition systems in planes are more about safety, if you have ever flown in a small plane you will notice the change in idle RPM when switching between each individual ignition system and both systems at once.
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How do you want to define performance? I would say multiple plugs/sparks would make for easier starting. Isn't that an increase in performance?

 

[FactChecker]

a two-stroke engine with one big cylinder may gain a real advantage in having two spark plugs to enable higher RPM.

I agree. In this case, the OP was about a 180 cc engine. That is a much smaller cylinder than in a typical 1,000 cc 4-cylinder bike. And so many 1,000 cc bikes rev high. So maybe the second plug is to get a more complete fuel burn and maximize the miles per gallon. Those 1,000 cc bikes are not the most fuel efficient.

The Mazda RX7 (wankel) used 2 plugs per rotor for years.

That makes a lot of sense from a fuel efficiency point of view. Wankel engines have a serious problem getting the fuel to burn before the exhaust path opens up. (see )

 

[Randy Beikmann]

Auto-ignition (spark knock) can easily happen if the flame initiated by the spark plug does not burn all the air/fuel quickly enough. As the flame progresses, the burnt mixture heats and compresses the unburnt mixture, which can ignite spontaneously if it remains at high pressure and temperature long enough. This is exacerbated by low-octane fuel or a high compression ratio.

So the best design to avoid knock is a compact combustion chamber with a central spark plug, reducing the distance the flame must travel to complete combustion. With today's typical 4-valve engines, that is easy (they can use a high compression ratio, and may not need as high octane fuel). But with 2-valve engines the plug needs to be to the side, so some designs have had twin plugs to speed up combustion. It's been most common in hemispherical heads, which produce a long curved combustion chamber, and otherwise have a tendency toward slow combustion and knock.

 

[HyperTechno]

How do you want to define performance? I would say multiple plugs/sparks would make for easier starting. Isn't that an increase in performance?

In a much smaller 180CC cylinder...? In a bigger engine it will make a difference. But... In a little bike engine, it may do a difference but not sure whether that increase in performance will worth the addition of 2plugs... Wouldn't it?

 

[john101]

Alfa twinspark.pdf

http://berlinasportivo.com/marquespec/Alfa/pdfs/twinspark.pdf

Performance Study on Twin Plug Spark Ignition Engine at Different Ignition Timings - MDIwMTMyNDM=.pdf

http://www.ijsr.net/archive/v2i8/MDIwMTMyNDM=.pdf

____________

I wonder if they tried a twinspark on the Wankel.

Another thought I had was it might be good to have a twinspark on a single cylinder (two ignition systems) simply because it will still run fine on one if one stops firing for some reason when pockets are empty or mechanic far away on a sunday night.

 

[Randy Beikmann]

In a much smaller 180CC cylinder...? In a bigger engine it will make a difference. But... In a little bike engine, it may do a difference but not sure whether that increase in performance will worth the addition of 2plugs... Wouldn't it?

Without test data, it is difficult to know. I would expect the effect to be smaller. But even small engines experience spark knock, and it's possible that two spark plugs could allow the engine to run with 1) a higher compression ratio, 2) more spark advance, and/or 3) lower octane fuel. Having these options can allow the engine to make more power or run more cheaply.

Edit: After reading the second file from john101, which was a study on a 100 cc engine, I guess the answer is that yes, it can make a difference!

 

[Ranger Mike]

here is some dyno info form my old hemi days
5to 10 hp on a 426 cubic inch chysler hemi..or about 1 hp additional per 53 cubic inch cylinder.
188cc is 12 cubic inch, by the way.
With a hemispherical, or flattened hemispherical combustion chamber of today, the quench areas are problematic for unburned fuel / high HC content in the exhaust. The opposed valve layout of the hemi chamber breathes well and makes mucho power, but requires more carp to pass current emissions law.
With the dual plug setup, it assures more complete combustion. Dual plugs shorten the flame front propagation and increase power for displacements of 175cc and greater.

This reduces NOx and ozone as we have full combustion and the by product of heat, water, and carbon dioxide. NOx emissions are only significant during incomplete or partial combustion, due to the lack of required oxygen, high temperatures, and various chemical reactions. The typical cure for the past 40 some years is to add a catalytic converter to burn off any residue. Adding the extra set of spark plugs on the HEMI reduced emissions to the point that no catalyst was needed. We had a lot less exhaust restrictions and thus we added more horsepower, but not very much. Maybe 10 horsepower maximum depending on muffles used.

Let me tell you the sad truth about the dual spark plug thing..its all about emissions. I reference my taking you back to the late Hemi racing days in Pro stock drag racing. Dick Landy did a masterful job pioneering the evolution of the dual spark plug hemi. By adding dual fired plugs on each cylinder, this allows the firing to take place closer to top dead center, and then again when the piston is on the back side of the power stroke. Dick had to re-angle the main spark plug 10 degrees tilted toward the exhaust rocker shaft but still on the center line, then he had to ad the extra spark plug at on center line but after TDC and canted 3 degrees rear ward an d tilted 2 1/2 degree “ upward” to yeild the best dyno results. With all the tweaking the result was 5 to 10 extra dyno Horsepower. What he did find out was the camshaft timing chain showed variance of up to 15 degrees ignition timing fluctuation. They ran dual distributors back then.

bottom line is ..ifgin you are in an airplane 10,000 feet above ground level, by all means add a second spark plug..but for a moped or small motor bike..no way..

 

[Randy Beikmann]

bottom line is ..ifgin you are in an airplane 10,000 feet above ground level, by all means add a second spark plug..but for a moped or small motor bike..no way..

It's great to hear a firsthand account of the Hemi story! I remember reading it, but it's good to hear it reiterated.

I agree the gains of the second plug are not earth-shaking (and 426 Hemi's shake the Earth quite a bit already). But they were necessary for them to get the last bit of advantage in a race.

In today's regulatory world, even small gains can't be ignored, to meet fuel economy and pollution standards. And I'm pretty sure that today's Chrysler Hemi's use 2 plugs, probably for that reason.

 

[HyperTechno]

Th

here is some dyno info form my old hemi days
5to 10 hp on a 426 cubic inch chysler hemi..or about 1 hp additional per 53 cubic inch cylinder.
188cc is 12 cubic inch, by the way.
With a hemispherical, or flattened hemispherical combustion chamber of today, the quench areas are problematic for unburned fuel / high HC content in the exhaust. The opposed valve layout of the hemi chamber breathes well and makes mucho power, but requires more carp to pass current emissions law.
With the dual plug setup, it assures more complete combustion. Dual plugs shorten the flame front propagation and increase power for displacements of 175cc and greater.

This reduces NOx and ozone as we have full combustion and the by product of heat, water, and carbon dioxide. NOx emissions are only significant during incomplete or partial combustion, due to the lack of required oxygen, high temperatures, and various chemical reactions. The typical cure for the past 40 some years is to add a catalytic converter to burn off any residue. Adding the extra set of spark plugs on the HEMI reduced emissions to the point that no catalyst was needed. We had a lot less exhaust restrictions and thus we added more horsepower, but not very much. Maybe 10 horsepower maximum depending on muffles used.

Let me tell you the sad truth about the dual spark plug thing..its all about emissions. I reference my taking you back to the late Hemi racing days in Pro stock drag racing. Dick Landy did a masterful job pioneering the evolution of the dual spark plug hemi. By adding dual fired plugs on each cylinder, this allows the firing to take place closer to top dead center, and then again when the piston is on the back side of the power stroke. Dick had to re-angle the main spark plug 10 degrees tilted toward the exhaust rocker shaft but still on the center line, then he had to ad the extra spark plug at on center line but after TDC and canted 3 degrees rear ward an d tilted 2 1/2 degree “ upward” to yeild the best dyno results. With all the tweaking the result was 5 to 10 extra dyno Horsepower. What he did find out was the camshaft timing chain showed variance of up to 15 degrees ignition timing fluctuation. They ran dual distributors back then.

bottom line is ..ifgin you are in an airplane 10,000 feet above ground level, by all means add a second spark plug..but for a moped or small motor bike..no way..

Very informatic. Thanks.

 

[HyperTechno]

Without test data, it is difficult to know. I would expect the effect to be smaller. But even small engines experience spark knock, and it's possible that two spark plugs could allow the engine to run with 1) a higher compression ratio, 2) more spark advance, and/or 3) lower octane fuel. Having these options can allow the engine to make more power or run more cheaply.

Edit: After reading the second file from john101, which was a study on a 100 cc engine, I guess the answer is that yes, it can make a difference!

Yes. That can make a difference. I doubted that considering the engine is very small, the advantage won't worth the cost of the addition of an extra spark plug. Well, in the long term it may be considerably advantageous(related to efficiency and environmental damage). Oh, even at a marketing standpoint, they can differ their bike from others considering not many bikes have twin spark plugs.

 

[Ketch22]

I have to agree with Ranger Mikes post. One of the "tricks" I have used in used often is; "When questioning a point carry it out towards the extreme and watch what happens." My experience in Blown Nitro engines is very similar to Ranger Mikes. By going to two plugs we improved engine life and bettered combustion. This was however on an engine that would destroy itself within 5 seconds. At least one of the 2 plugs was gone within 0.7 seconds of coming of the line. Does the second plug contribute? Unequivically, yes. Is it a factor to be considered at a smaller more conservative usage, probably not. The team I worked with saw more than 200% increase in life. (1 plug dead in 0.75 seconds to 1 of 2 dead in 0.75 seconds the other lasted as much as 1.25 sec. Not a statistically significant improvement for a small conventional engine.

 

[Quickbobo]

I think alota people missed the point here... The key word in the post was "India". The fuel quality there is crap, outside of major cities! The use of dual plugs allows the ignition timing to be "retarded" to avoid knock, as the combustion is propagated on 2 fronts. I found as the builder of numerous twin plug H-D street and race engines, on the shop dyno, (YES, it was RECOMMENDED, we retard the timing 3-5 degrees) it also dropped the cylinder head temps, very important on air cooled engines that operate in hot climates, on primitive road systems, or crowded cities.

 

[mrm11]

if you carry out a simple experiment and see that if the engine runs smoothly with one spark-plug, you will see it does with this small engine.
No significant change in the noise or in fact power of the engine.
Only the main spark-plug should be on the engine, it hardly matters that the other is on or not.
this bike has a hemispherical combustion chamber, with little swirl to promote better combustion. Obviously two spark plug adds to the cost in form of a new ckt, cdi, new cylinder head etc in addition to the cost of plug.
In my opinion cost is more then the return.

 

[HyperTechno]

if you carry out a simple experiment and see that if the engine runs smoothly with one spark-plug, you will see it does with this small engine.
No significant change in the noise or in fact power of the engine.
Only the main spark-plug should be on the engine, it hardly matters that the other is on or not.
this bike has a hemispherical combustion chamber, with little swirl to promote better combustion. Obviously two spark plug adds to the cost in form of a new ckt, cdi, new cylinder head etc in addition to the cost of plug.
In my opinion cost is more then the return.

May be the marketing effect could result in a good return!

 

[Rx7man]

If the two plugs are fired simultaneously (they probably are), the additional cost of adding a second spark plug is in fact very small... There's the cost of the plug, drilling and tapping the head, and using a 'waste spark' coil that has 2 wires on it.. No extra CDI unit is needed

While there may be some reliability benefits, power benefits would be small... I do think it was a cheap way to stand out and use it for marketing.

 

[mrm11]

If you have to place one spark plug on the engine...you will have it placed at the center if the head so that the spread of flame is uniform and flame front reaches uniformly.
Now...on the other hand if you place two spark plug what will you do------shift them to the corners...
so the fame from one plug eats the fuel and the corner fuel is burnt by the other plug...that is the idea...so there is some lag in the spark timing of the plugs...and hence new lag from somewhere has to be there.
to make the long story short...you have to adjust the spark timing and the CDI just does that...

 

[Rx7man]

I'm not sure a delay between plugs is necessary.. having them fire at the same time just means you have 2 flame fronts.. Yes, you would place them on the sides of the combustion chamber, and the dual plug setup is probably more detonation resistant than a single, center fired plug because instead of 1 flame front progressing toward the corners with a huge pressure wave, and having fuel in the corners to preignite and nowhere to go, the dual plug setup would burn a lot of the fuel in the corners first, and the colliding high pressure waves wouldn't really matter all that much since the fuel is already burnt or burning and it would have somewhere to go..

https://en.wikipedia.org/wiki/Dual_ignition

A further form of partial dual ignition (such as on the Honda VT500) is for each cylinder to have a single HT coil which sends the current to one plug and completes the circuit via the second plug, rather than via the earth, the current necessarily jumping two plug gaps.

I would guess this is the style used in this motorcycle as well.. the ignition is much like a waste-spark system, where 1 coil fires 2 spark plugs in 2 cylinders, but instead both plugs are in the same cylinder.
Bottom of this page there's a blurb on single cylinder use as well
https://en.wikipedia.org/wiki/Wasted_spark

 

[mrm11]

In this particular case detonation seems not to be a problem. The phenomena is well explained above.
Many other methods are there to reduce detonation as pre-cooling the charge, changes in air fuel ratio or spark timing change.
I think in this case it is necessary to ignite the fuel completely to achieve good fuel efficiency as mentioned in the first statement of post.
If due to some reason the condition in some particular area in combustion chamber remains no more suitable for good ignition the flame will extinguish or burning will not be adequate.
You will have to start the combustion at that area instantaneously.
Obviously then you will have to put some delay.

 

[rnicest]

Most small engines use magnetos which put out a "weak" spark, and are therefore more prone to "misfiring" than a battery powered system. Two plugs per cylinder greatly reduces the percentage of the time that "misfires" occur because there is only a small chance that both plugs will misfire at the same time. This increases power and makes exhaust emissions be cleaner. Two plugs per cylinder also effectively increases "flame speed" which means you can retard the timing some and pick up some power that way.

 

[Flyboy]

Chiming in with the perspective of an aircraft mechanic...
Aside from the obvious benefit of reliability, as pointed out many years ago at the start of the thread, there is actually a slight performance advantage to using two spark plugs. One of our regular checks on light airplane engines is to go to 1800 rpm and disengage one of the magnetos (the planes use two independent, self-contained magnetos, again for reliability), and we should see a 50-100 rpm drop off. Granted, fuel mixture can also impact this figure, but usually any variation can be laid at the feet of a mistimed magneto.
The bigger benefit is a more even flame front in the cylinder, providing a more smooth impulse on the piston.

 

[berkeman]

One of our regular checks on light airplane engines is to go to 1800 rpm and disengage one of the magnetos (the planes use two independent, self-contained magnetos, again for reliability)

So each of the magnetos feeds one set of spark plugs for redundancy? Interesting...

 

[Flyboy]

So each of the magnetos feeds one set of spark plugs for redundancy? Interesting...

Not only that, but they usually feed the top of one side of the engine, and the bottom of the other side. So, for example, left magneto will feed the top of the right side and the bottom of the left, and the right mag feeds the top of the left and the bottom of the right. At least on the opposed engines most often used.

Don't ask me to explain how they do radials and vee-type engines. I haven't touched a radial since school three years ago, and that was more prepping it for running it on the test stand, not running the ignition leads.

 

[Tom.G]

Fire Trucks (at least used to) have dual spark plug/ignition systems for reliability.

 

[Baluncore]

So each of the magnetos feeds one set of spark plugs for redundancy? Interesting...

During WW2, the test before takeoff was to run the engine up to temperature and speed, then cut one magneto at the time to check the fall in RPM. A "magdrop" of more than say 150 RPM, cancelled the flight.

I have a double toggle switch panel somewhere here, labelled "Magnetos".

 

[OCR]

I haven't touched a radial since school three years ago...

Lol, I haven't touched a radial since A&P school. . . 50 years ago. ( 1973 )

.

 

[gmax137]

When I was about 14, I wandered into the local Euro-Sports-Auto sales lot. They had a red Ferrari with the hood up. I spent quite a few minutes looking at the engine. Counted the 12 spark plug wires. Eventually I asked the sales guy "why are there two spark plugs per cylinder?" -- annoyed, he told me "that's a twelve cylinder engine, kid."

Much later I had a hot-rodded HD sportster with dual plugs. As mentioned above, this does allow for less spark advance, a lot less.

 

[Averagesupernova]

I recall seeing Honda Odyssey many years ago with two plugs. (Not the car) It was only a single cylinder engine. Two stroke I would assume.

 

[Averagesupernova]

And according to eBay, here is one.

 

[gmax137]

Sometimes, the second "plug hole" is for a compression release. Seen on old Brit bikes, if they don't have a "valve lifter."

 

[Flyboy]

During WW2, the test before takeoff was to run the engine up to temperature and speed, then cut one magneto at the time to check the fall in RPM. A "magdrop" of more than say 150 RPM, cancelled the flight.

I have a double toggle switch panel somewhere here, labelled "Magnetos".

Exactly right. Still done today on light piston planes, although it's more of a maintenance check every so often.

 

[Averagesupernova]

Sometimes, the second "plug hole" is for a compression release. Seen on old Brit bikes, if they don't have a "valve lifter."

That could be but I do recall a plug in each hole and a wire on each. The Odyssey I used to ride only had one and I don't recall a comp release.

 

[gmax137]

That could be but

Sorry @Averagesupernova , my comment was not directed at your photo. More of a general comment.

 

[Averagesupernova]

Sorry @Averagesupernova , my comment was not directed at your photo. More of a general comment.

Hey that's ok.