4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

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4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by nicholastanguma »

This question is about performance engine design, not better emissions design.

Dual spark heads make good sense for cylinder bores of significant size, especially in air cooled engines: flame propagation is faster in the chamber, which allows for less ignition advance, which allows for higher compression with less pinging. Great, and a trick engine tuners have been using for decades.

But the higher the rpms go with these large cylinder bores the more potential there is for twin plug heads to suffer complications. Two sparks and two flame fronts can make the combustion happen too rapidly causing pressure in the cylinder to build up too fast. There can also be problems with large throttle openings at high rpms, when the two flame fronts inside the combustion chamber collide with such force they produce shockwaves which can damage the engine.

BMW and Suzuki, starting way back in 2009 (BMW even before then, I think), addressed this potential high rpm/wfo throttle issue by having a separate ignition timing map for each plug within the same cylinder, so as to delay the timing of one plug behind the other at high revs.

Now assume a big bore cylinder with a 4 valve head, such as Harley-Davidson's new Milwaukee Eight engine, but using a single centrally located spark plug.


Does this single centrally located spark plug actually perform better in a 4 valve head than would a dual plug design--meaning, it propagates flame across the chamber as well as dual plugs but without the potential high rpm/wfo throttle problems associated with dual plugs?
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by ptuomov »

What does this mean? "when the two flame fronts inside the combustion chamber collide with such force they produce shockwaves which can damage the engine."
nicholastanguma wrote: Wed Aug 17, 2022 7:59 am This question is about performance engine design, not better emissions design.

Dual spark heads make good sense for cylinder bores of significant size, especially in air cooled engines: flame propagation is faster in the chamber, which allows for less ignition advance, which allows for higher compression with less pinging. Great, and a trick engine tuners have been using for decades.

But the higher the rpms go with these large cylinder bores the more potential there is for twin plug heads to suffer complications. Two sparks and two flame fronts can make the combustion happen too rapidly causing pressure in the cylinder to build up too fast. There can also be problems with large throttle openings at high rpms, when the two flame fronts inside the combustion chamber collide with such force they produce shockwaves which can damage the engine.

BMW and Suzuki, starting way back in 2009 (BMW even before then, I think), addressed this potential high rpm/wfo throttle issue by having a separate ignition timing map for each plug within the same cylinder, so as to delay the timing of one plug behind the other at high revs.

Now assume a big bore cylinder with a 4 valve head, such as Harley-Davidson's new Milwaukee Eight engine, but using a single centrally located spark plug.


Does this single centrally located spark plug actually perform better in a 4 valve head than would a dual plug design--meaning, it propagates flame across the chamber as well as dual plugs but without the potential high rpm/wfo throttle problems associated with dual plugs?
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by MetricMuscle »

nicholastanguma wrote: Wed Aug 17, 2022 7:59 am But the higher the rpms go with these large cylinder bores the more potential there is for twin plug heads to suffer complications. Two sparks and two flame fronts can make the combustion happen too rapidly causing pressure in the cylinder to build up too fast.
Wouldn't this just be a timing issue? If peak cylinder pressure is too early then less advance would move it later.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by ptuomov »

MetricMuscle wrote: Wed Aug 17, 2022 12:53 pm
nicholastanguma wrote: Wed Aug 17, 2022 7:59 am But the higher the rpms go with these large cylinder bores the more potential there is for twin plug heads to suffer complications. Two sparks and two flame fronts can make the combustion happen too rapidly causing pressure in the cylinder to build up too fast.
Wouldn't this just be a timing issue? If peak cylinder pressure is too early then less advance would move it later.
I think the paper attached to the post above says that measurement location for the knock index computation matters. Also, the spark plug location matters. I think the four valve head geometry would work the best with three spark plugs. The tumble seems to work beautifully with one spark plug but might get disrupted by adding only one plug because that has to be added to either side.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by nicholastanguma »

I found this terrific technical analysis of the Ducati 1299 Panigale superbike engine.
https://www.cycleworld.com/2015/01/26/ ... th-photos/

Its forebear, the 1199 Panigale, was characterized by a MONSTROUS differential between bore and stroke, in fact, at the time of its manufacture the most radically over-square bore and stroke measurements ever adopted on a road worthy twin-cylinder motorcycle engine: 112mm x 60.8mm.

Then, in 2015, the 1299 took that to the next level up: 116mm x 60.8mm.

And here's a clear close-up of the cylinder head: one centrally located spark plug, surrounded by 46.8mm inlet valves and 38.2mm exhaust valves. Yes, engineering is always about compromises, but Ducati's former flagship model seems to be a pretty good indication of what works well, I suppose.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by englertracing »

Ktms less powerful older rc8 engine used two plugs
3QEL2YLA2HSVYIKNVTS45EGJ3Y.jpg
I think it would be difficult to fit 3 because of Valvetrain
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by MetricMuscle »

englertracing wrote: Thu Aug 18, 2022 3:43 am Ktms less powerful older rc8 engine used two plugs. I think it would be difficult to fit 3 because of Valvetrain
Honda does this with their CRF1000L Africa Twin.

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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by nicholastanguma »

Fueling is the company that developed high performance 3 valve head design in the modern age. The company is so good at it they licensed the tech to Ford for the FoMoCo's Modular 3 valve engines back in the (relatively recent) day. The Fueling design utilizes a single, centrally located spark plug. In the early 2000's, if I remember correctly, Ford experimented with dual plugging some of the higher performance V8 Modular variants, presumably because of emissions standards and not because of actual performance enhancement.

The new H-D Milwaukee 8's four valve design works very well in stock form, but when high performance tomfoolery gets thrown into the mix, such as high comp pistons, high lift cams, all that sort of good stuff, the bridge between the engine's two exhaust ports gets overheated beyond factory design parameters.

So in 2022 Fueling started prototyping a bolt-on high performance head for the Milwaukee 8 to address this issue. Aaaaaand...yes, predictably, it's a 3 valve head design, with a single centrally located spark plug.

In the 70s Honda was utilizing 3 valve heads on various models, and by the 80s (or the 90s, I'm not entirely certain), they had settled on 3 valves with dual spark plugs. As far as I know they never used a single, centrally mounted spark plug, I don't know why.

https://www.youtube.com/watch?v=AY0yeZdcwok

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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by ptuomov »

My guess is that any four valve head that relies on barrel tumble charge motion, will run well with one or three plugs at peak torque and above.

At low rpms when there isn’t enough ruble motion, an asymmetric two plug setup may be helpful in a four valve head to produce swirl. At peak torque rpm and and above, I’d fire the second plug way late such that it stays clean but doesn’t screw ip the charge motion.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by nicholastanguma »

MetricMuscle wrote: Wed Aug 17, 2022 12:53 pm
Wouldn't this just be a timing issue? If peak cylinder pressure is too early then less advance would move it later.

It does indeed also seem to me that retarded advance would solve the issue. I'm not certain why the companies' engineers didn't just employ this tactic. Clearly there must be something else about the issue that we're not thinking of here.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by hoffman900 »

nicholastanguma wrote: Wed Aug 17, 2022 7:27 pm I found this terrific technical analysis of the Ducati 1299 Panigale superbike engine.
https://www.cycleworld.com/2015/01/26/ ... th-photos/

Its forebear, the 1199 Panigale, was characterized by a MONSTROUS differential between bore and stroke, in fact, at the time of its manufacture the most radically over-square bore and stroke measurements ever adopted on a road worthy twin-cylinder motorcycle engine: 112mm x 60.8mm.

Then, in 2015, the 1299 took that to the next level up: 116mm x 60.8mm.

And here's a clear close-up of the cylinder head: one centrally located spark plug, surrounded by 46.8mm inlet valves and 38.2mm exhaust valves. Yes, engineering is always about compromises, but Ducati's former flagship model seems to be a pretty good indication of what works well, I suppose.
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Ducati has talked a lot about using tumble to make these large bores work. That said, with their performance options, they said they were not going to go any larger than 100mm bores for combustion quality reasons.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by englertracing »

hoffman900 wrote: Fri Aug 19, 2022 10:40 am
nicholastanguma wrote: Wed Aug 17, 2022 7:27 pm I found this terrific technical analysis of the Ducati 1299 Panigale superbike engine.
https://www.cycleworld.com/2015/01/26/ ... th-photos/

Its forebear, the 1199 Panigale, was characterized by a MONSTROUS differential between bore and stroke, in fact, at the time of its manufacture the most radically over-square bore and stroke measurements ever adopted on a road worthy twin-cylinder motorcycle engine: 112mm x 60.8mm.

Then, in 2015, the 1299 took that to the next level up: 116mm x 60.8mm.

And here's a clear close-up of the cylinder head: one centrally located spark plug, surrounded by 46.8mm inlet valves and 38.2mm exhaust valves. Yes, engineering is always about compromises, but Ducati's former flagship model seems to be a pretty good indication of what works well, I suppose.
Image
Ducati has talked a lot about using tumble to make these large bores work. That said, with their performance options, they said they were not going to go any larger than 100mm bores for combustion quality reasons.
But they did... they went 116mm and made 210is hp from 1299cc.
I suppose its not that impressive as the 4 cylinder 1000s are there at 200hp as well
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by hoffman900 »

englertracing wrote: Fri Aug 19, 2022 1:27 pm
hoffman900 wrote: Fri Aug 19, 2022 10:40 am
nicholastanguma wrote: Wed Aug 17, 2022 7:27 pm I found this terrific technical analysis of the Ducati 1299 Panigale superbike engine.
https://www.cycleworld.com/2015/01/26/ ... th-photos/

Its forebear, the 1199 Panigale, was characterized by a MONSTROUS differential between bore and stroke, in fact, at the time of its manufacture the most radically over-square bore and stroke measurements ever adopted on a road worthy twin-cylinder motorcycle engine: 112mm x 60.8mm.

Then, in 2015, the 1299 took that to the next level up: 116mm x 60.8mm.

And here's a clear close-up of the cylinder head: one centrally located spark plug, surrounded by 46.8mm inlet valves and 38.2mm exhaust valves. Yes, engineering is always about compromises, but Ducati's former flagship model seems to be a pretty good indication of what works well, I suppose.
Image
Ducati has talked a lot about using tumble to make these large bores work. That said, with their performance options, they said they were not going to go any larger than 100mm bores for combustion quality reasons.
But they did... they went 116mm and made 210is hp from 1299cc.
I suppose its not that impressive as the 4 cylinder 1000s are there at 200hp as well
This was in reference to the Panigale and the “race” stuff. They’re still using larger bores on other stuff that isn’t chasing every last drop of power.

What I think is most impressive is Ducati is able to get good combustion at rpm’s exceeding 12,000rpm with 116mm bores, with a single plug on pump gas.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by nicholastanguma »

hoffman900 wrote: Fri Aug 19, 2022 3:45 pm
This was in reference to the Panigale and the “race” stuff. They’re still using larger bores on other stuff that isn’t chasing every last drop of power.

What I think is most impressive is Ducati is able to get good combustion at rpm’s exceeding 12,000rpm with 116mm bores, with a single plug on pump gas.

There are plenty of modern moto engines--modern I suppose meaning designs from the last 20 years or so--that use twin plugs, but it seems to me there are more with single plug. Admittedly, I've never taken an official survey, so I could be wrong about this.

In former times, when two valve head design was the norm, some form of hemispherical combustion chamber shape was the norm, too. Ergo twin plugs provided some real performance benefits, however small or large per application.

Modern combustion chamber design favors compactness and large squish area, and coupled with modern flat top piston design, I'm kind of having trouble believing that twin plugs provide better performance than a single centrally located plug.

That being said, I obviously don't know for certain, or else I wouldn't have started this thread. If I'm wrong please do correct me.
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Re: 4 Valve Head: Single Central Spark Plug vs Dual Spark Plugs

Post by Tom68 »

nicholastanguma wrote: Sun Aug 21, 2022 7:44 am
hoffman900 wrote: Fri Aug 19, 2022 3:45 pm
This was in reference to the Panigale and the “race” stuff. They’re still using larger bores on other stuff that isn’t chasing every last drop of power.

What I think is most impressive is Ducati is able to get good combustion at rpm’s exceeding 12,000rpm with 116mm bores, with a single plug on pump gas.

There are plenty of modern moto engines--modern I suppose meaning designs from the last 20 years or so--that use twin plugs, but it seems to me there are more with single plug. Admittedly, I've never taken an official survey, so I could be wrong about this.

In former times, when two valve head design was the norm, some form of hemispherical combustion chamber shape was the norm, too. Ergo twin plugs provided some real performance benefits, however small or large per application.

Modern combustion chamber design favors compactness and large squish area, and coupled with modern flat top piston design, I'm kind of having trouble believing that twin plugs provide better performance than a single centrally located plug.

That being said, I obviously don't know for certain, or else I wouldn't have started this thread. If I'm wrong please do correct me.
I'd imagine it's about acceptable misfire limits, with throttled driving and EGR there's a lot of incombustible mixture in the chamber and only one little spark to ignite the combustible portion. Still if things get hot enough from compression you can still have combustion after the timed ignition point.
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