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Does using dual spark plugs per cylinder make any difference?

  1. Nov 5, 2016 #1
    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.
     
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  3. Nov 5, 2016 #2

    FactChecker

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    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.
     
  4. Nov 5, 2016 #3

    Baluncore

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    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.
     
  5. Nov 5, 2016 #4

    Ranger Mike

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    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.
     
  6. Nov 5, 2016 #5

    Nidum

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    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 .
     
  7. Nov 5, 2016 #6
    That's a 4 strock engine.
     
  8. Nov 5, 2016 #7
    But this is a motor bike and not a racing bike, one designed for regular use. The engine is just , 180CC.so...
     
  9. Nov 5, 2016 #8

    Averagesupernova

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    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.
    -
    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?
     
  10. Nov 5, 2016 #9

    FactChecker

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    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.
    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 )
     
  11. Nov 5, 2016 #10

    Randy Beikmann

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    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.
     
  12. Nov 5, 2016 #11
    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?
     
  13. Nov 6, 2016 #12
    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.
     
  14. Nov 6, 2016 #13

    Randy Beikmann

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    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!
     
    Last edited: Nov 6, 2016
  15. Nov 6, 2016 #14

    Ranger Mike

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    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..
     
  16. Nov 6, 2016 #15

    Randy Beikmann

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    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.
     
  17. Nov 6, 2016 #16
    Th
    Very informatic. Thanks.
     
  18. Nov 6, 2016 #17
    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.
     
  19. Nov 8, 2016 #18
    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.
     
  20. Nov 22, 2016 #19
    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.
     
  21. Dec 18, 2016 #20
    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.
     
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