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Technology - Reasons for 2 spark plugs per Cylinder ?

13K views 41 replies 18 participants last post by  D.T. 
#1 ·
I know this Technology is not new and has been seen for many years in other industry's.

But how does this application benefit from the 2 plug per head design.?

Better fuel economy, Improved throttle response, Lower emissions , etc.

I might have the bases covered above but are there other reasons ?


And my first question is : if one of the plugs stopped working would you know it ?

Trigger check engine light ? Engine rpm stumble ? :confused:
 
#2 ·
#3 ·
I think combustion efficiency is the main reason. Piston engine aircraft have run a dual magneto/ spark plug arrangement for years. Mainly for redundancy in case a magneto fails. Part of a pilots and mechanics check is a magneto drop test. During engine runup at a specified RPM each magneto is shutoff to check the other. There was usually about a 150 RPM drop with one mag switched off.
 
#4 ·
Initial reasons for two spark plugs per cylinder were for reliability. Spark plugs commonly fouled decades ago.

Then they were used to lower emissions. And to increase power. Some combustion chamber designs are more efficient than others. Adding a second spark plug would help a less efficient design meet emissions requirements or produce more power.

Why does a second spark plug lower emissions or increase power? It adds a second flame front. When the fuel/air mixture ignites, how it travels from that point has a lot to due with how well the fuel/air mixture is consumed. There can be pockets of mixture that don't "burn" due to stagnant movement or other issues that combustion chamber has. The further a flame front travels, which takes time, the more likely the controlled burn can become out of control and explode ( detonation ). By using a second flame front provided by a second spark plug, the distance traveled is reduced, as is time for the mixture to completely burn, and this tends to more completely burn the fuel/air mixture. This reduces hydrocarbon emissions, lessens detonation issues. And a by product is increased power for the same amount of fuel used.

A really good combustion chamber design may not benefit from a second spark plug ( which in itself complicates combustion chamber design ).
 
#5 ·
I would think it might be more likely to decrease emission levels due to the fact that one plug is on the side of the head
and one is located more central to the head nearer to the intake and exhaust valves.
 
#7 · (Edited)
Do many ( or any) of the newer motorcycles other than Suzuki use this design engineering Trait ?


It is amazing that they are able to squeeze allmost 70 h.p from a 650 cc 2 cylinder engine ( in my case )

I have seen Single Cylinder Briggs and Stratton engines used in Junior dragsters Hopped up to the point
they run Alcohol /methanol and turn more than 8000 rpm. and 50 h.p And these are just run of the mill
5 h.p go kart engines that have been extensively modified. You have to give these engineers a lot of credit for
knowing how to make power in a small package. Motorcycle engineers just do it with a warranty in mind.
 
#11 ·
Not sure I agree with this, as all the motorcycle companies are fully embracing "good technology" IMHO. Suzuki saves money by using budget brakes and suspension, plus whatever else in the parts bin can be transferred to another model, this is a pretty common practice all around. The Stroms for example are being improved with every edition, they can hopefully only get better. :fineprint:
 
#12 ·
I kind of think this is a trend. If you market a great all around motorcycle like the Vstrom series (lots to offer )
In a durable powerful package - they will come. And if sales figures remain actively brisk number crunchers will
keep it in play. Similar to what Honda has done with the tried and true entry level Rebel 250. Which has been
around for over 25 years.

To me the Vstrom has a gem of a motor. And an easy platform to season to taste. :)
 
#14 ·
You know it could very well be a time for Suzuki to shine. In the auto industry with so many players at the table,
all it takes is one manufacturer to come out with a design thats a real hit with consumers and then everyone wants
to build something that looks like it or is very similar to it. This means they try to steal market share from the ones
getting the big sales figures. Copy catting. Think about how many bikes out today have the pointed beak style the Vstrom
has had for several years. Not that they were first , but they offer something that covers all the bases which makes it a home run.

It's what farkles are made for ....:var_17::wink2:
 
#16 ·
Has to be for combustion efficiency. Emission Reduction.

I think it may decrease horsepower though. GSXR's don't have 2 SP heads and pass emissions testing.

I just converted my L2 to stick coil single spark plug firing.

Now you wonder if dual spark plug electrodes or E3 spark plug design increases...what? :confused:
 
#17 ·
Back in the early 70's I rode several 2 stroke dirt bikes that had twin plug heads. One was for the sprk plug and the other
was for a spring loaded cable operated compression release. You used the lever on the bars to dump compression prior
to entering a corner. It was like brakes. it just slowed you down. Ahhh the good ole days.....
 
#19 ·
I owned a 1984 KDX200 to which I added a decompressor by drilling an extra spark plug hole into the head and fitting the unit there.
It was great on steep downhills and in slippery terrain. Maximum braking without any chance of locking up the rear wheel.

Unfortunately Kawasaki then introduced water cooling.
 
#20 · (Edited)
To get fuel to ignite properly you need the correct mix of fuel and air at and near the ignition point and a source of heat, like a spark.

Sounds simple, but what actually happens in an engine is pretty complex and not only depends on things like air pressure, temperature, rpm and fuel but also on what happened on the last stroke. Some of the air coming in tends to bounce and the same thing happens at the exhaust. The resuit with a single plug engine in a good state of tune is the occasional misfire due to the mix being way off at the point where the spark is. Maybe 1% or so of cycles. That also tends to screw things up somewhat on the next cycle as well.

A second spark reduces the odds of that happening, the 1 in 100 odds drop to perhaps 1 in 10,000 and make for a smoother feeling engine and better emissions performance. It's mainly emissions that's the problem for a bike engine, a car can have a large enough exhaust and cat to get rid of the effects of unburned fuel before it exits the tailpipe, a bike, not so much.
 
#24 ·
Depends

Flame speed is pretty constant in a combustion chamber. In a physically large combustion chamber it takes longer to complete combustion. Such a chamber is usually more susceptible to detonation as well. So you have conflicting needs to retarded timing to avoid detonation, but a need to advance it to allow more complete combustion. And higher-octane fuels are generally unavailable. A second ignition course can reduce the flame travel time, and perhaps increase turbulence which may increase flame travel speed.

Aircraft engines operate in prime detonation territory, low revs (2700 RPM) and high loads. Most were also air-cooled. Traditionally high-octane leaded fuel was used to provide a margin of safety. Unfortunately the lead tends to accumulate on spark plugs and foul them, especially if the pilot doesn't lean the mixture when appropriate.

Well-designed combustion chambers usually try to confine the air-fuel mix to a relatively small volume at top dead center, minimizing the travel distance.

If you add a plug, be interesting to put a knock sensor on the head and fiddle the timing. Might get significantly more power, assuming the other systems are up to it. I believe some manufacturers also fired the plugs at different times, an additional area of experimentation.

Evidently Bosch is experimenting with a microwave ignition source that ignites the entire charge simultaneously. Seems to me that would be very similar to detonation, so presumably they'll be experimenting with very lean-burn engines, or perhaps sequential fuel injection.
 
#25 ·
Evidently Bosch is experimenting with a microwave ignition source that ignites the entire charge simultaneously. Seems to me that would be very similar to detonation, so presumably they'll be experimenting with very lean-burn engines, or perhaps sequential fuel injection.
Igniting the whole charge simultaneously would essentially eliminate the possibility of detonation. Remember, detonation is not a normal combustion process, but an extremely rapid "explosion" like process (thus the name "detonation"). If the whole charge is simultaneously ignited there will be no chance for the unstable compounds to form which cause detonation.

Detonation is also not the result of multiple flame fronts reaching each other. If it was, adding a second spark plug would cause detonation, not help to avoid it. It is the detonation itself which creates shock waves and high pressure spikes during the combustion process.
 
#26 ·
the reason Expansion chambers work so well on 2 stroke engines is the power pulse wave that bounces back to the cylinder which
helps fill the cylinder with a fresh charge on the next cycle. Evacuation - fill - Evacuation - fill These pulses help the engine develope
more power without any changes anywhere else. A rather novel idea.
 
#27 ·
Detonation

Detonation is the result of radiated heat igniting the fuel mixture ahead from the flame front, rather than the orderly progression of combustion. So rather than a smooth increase in cylinder pressure, you get big spikes, which are hard on bearings and other stress-carrying parts. The extreme turbulence also scrubs the thin stagnant layer of insulating gas off the top of the piston, exposing the aluminum to temps it can't handle.

Two flame fronts, assuming they are 'orderly', may reduce the chances of detonation, so long as they reduce the overall time to complete combustion. That's the point of dual-plug heads.

The problem with the microwave ignition as I see it is that it would act very similar to detonation. Rather than an orderly burn that smoothly increases pressures, all the fuel burning all at once would be more like an explosion. Very hard on bearings and parts. Possibly a pre-chamber design with metered flow to the main combustion chamber would work. Or, as I said, sequential fuel injection. Inject a little fuel, burn it, inject a little more, etc.
 
#31 ·
^
My Son still had his 2004 DL 650 when I bought my new 2012 DL 650. I weigh more than him by quite a few pounds. The 2012 would pull away from the 2004 anywhere at any time. And usually averaged about 1-2 mpg better on trips.

Horsepower isn't everything. I think some places had the peak horsepower at a lower number on the 2012 and up DL 650. But average HP under the curve was very much in favor of the 2012 and newer engines. Where his 2004 didn't want to be run under 4000, the 2012 was quite happy running around town at 3000 rpm.
 
#36 ·
I don't think we pay enough attention to spark plugs.

My dad was a automotive parts wholesaler and a huge part of his business was Champion Spark Plugs.

I caught up with my dad for lunch one day and he had invited one of the big wigs from Champion Australia.

The conversation soon turned to cars and bikes, he quickly told me I could gain 8hp at the rear wheels of my car if I reduced the gap on my plugs from the recommended .059" to .057" but the motor would not be as smooth in the lower RPM's.

I then asked about my 1997 KDX200, I had spent a lot of time playing with the carburettor jets but I could never get it perfect, if it was crisp and clean down low it would be fluffy up top or if I got it crisp up top it would be fluffy down low, he asked what plug I had in there, NGK B8ES.


A few days later I got some champion plugs in the mail, N2g & N3g (gold), the performance difference was outstanding, no more fluff just crisp and clean at all throttle openings.

After that I got my dad to get me a few boxes of them, I ended up owning every N2g & N3g in Australia at the time, every time one of my mates or even strangers fouled a plug I would fit one of my special plugs as they came to be known, they never fouled and it turned out when my mates sold their bikes they would keep the spark plug and move it to their new bikes.

My dad had a customer that raced go-carts, he always ran in the middle of the pack until I suggested he try a N3g plug, he started to win races and was so impressed with the plug he scared the outside of the plug so know body at a race meeting could tell what plug he was running.


I still keep some N3g's in the shed but I now import them from the UK.


Until that first lunch I never gave spark plugs much thought.
 
#38 ·
I ran B8ES in just about all my bikes back then. Never a problem. I did a seminar by a Champion rep way back in the early 80s. He told me the reason their spk plugs had gotten better was they copied NGK. (True story). Possibly that "Special" spark plug was fixing a jetting issue?
 
#37 ·
If only this twin plug technology was introduced back in the late 60's, for our two strokes, I wouldn't have to had to clean / thrown away so many spark plugs. Synthetic oil in a two stroke was also a marvelous discovery for spark plug life. LOL
 
#39 ·
It didn't just fix my jetting it fixed everybody's.

As I said I spent hours with different jets and needles trying for perfection, I was unable to get that with the NGK plugs but it was quick and easy with the Champion Gold.
 
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