Multi Spark Plugs 1

[thundair]

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....

 

[swall]

NickE--EngJW pretty much nailed it. For the specifics on the BMW engines, all that was needed was to replace the two single lead coils with two dual lead coils, add a high voltage amplifier for the triggering current and drill/tap the heads for the second plug. It was put in on the bottom side of the cylinder head. If you have a mental picture of the BMW down the street, you will remember the spark plug on the top side of the cylinder.

 

[j2bprometheus]

hydrae -

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

 

[WilliamH]

Valid reasoning for utilizing dual spark plugs in automotive engines can be easily justified.

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.

 

[thundair]

That was really my concern was, what would the flame front look like, and would there be detonation or knock from such a fast burn.

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.

 

[kenre]

Bit of thinking out of the box.....

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

 

[NickE]

"The Turbo charged engine has such an active chamber (swirl/tumble/etc.) that it does not respond to the twin plug deal as well."

Is that in general for turbocharged, or is combustion chamber design still the big factor?

 

[WilliamH]

NickE,

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

 

[rdd48856]

The latest from Honda. Spark plugs are fired sequentialy, not simultaneoulsy....

http://www.hondacarindia.com/city/images/performance/idsi_engine_pop2.jpg