Denso's Twin Tip spark plugs
 

I read about Denso's TT spark plugs in a mag the other day and the principle seemed OK: The spark jumps between two tips, both have smaller than usual diameter which supposedly allows lower voltage, etc. Then the claims: Increased power, 5% lower fuel consumption. Yeah, right.

easiest path to ground
 

there will not be spark at both electrodes , the spark will take the single easiest pathway to ground ,
which may vary as the gap erodes and conditions inside the combustion chamber change .

spark plugs with two and more electrodes were OEM specified by many , including VW Audi , Toyota - there was a difference in how the engines ran and overall emissions if the OEM recommendation / specification for spark plugs was not strictly adhered to .

but
on later current production VWs at least
the newest systems use only single electrodes , with multi strike spark

having said that
never use Bosch Platinum +4 or +2 spark plugs , they were never OEM specified for any system and do not perform as well as
the correct OEM specified part# for the system in question

Sparks also jump easiest from a sharp edge or point and not from a rounded nub, that is why NGK V-power plugs seem to work well, the center contact has a simple v grove creating two points for sparks to jump, of course the sharp edge of a standard post works well too, splitting the electrodes is not a new idea.
If you really want to get in deep, the SAE published a book a while back on spark plugs and spark plug design and explained a lot of the ideas behind some of the different designs along with their draw backs.

When the Splitfires came out years ago, I remember that one of their marketing explanations was that the ground electrode was split in order to expose more of the fuel vapor to the spark. I was never sure about the efficacy, though, since it always seemed to me that they were counting on people's infrequent maintenance of their spark plugs (gapping, replacing, etc.) for all of their claimed gains.

If you really want to improve a sparkplug the best way is to use a radioactive element in the electrodes. This ionizes the gases between the spark gap thus making a hotter and fatter spark. Corrosion and fouling of the plug will inhibit the effectiveness of this so it would be best combined with a platinum plug technology. Of course whether you could see a difference from tank to tank is still debatable. :)

From what I've read on these forums (and if I haven't mixed it up), the actual combustion process itself is very close to something like 95% or 99% efficient. Anything that improves on that, even bumping it up to 100% efficient, still won't be noticeable by the time it goes through the drivetrain and wheels. It MAY barely help (performance and/or emissions) in an old engine in desperate need of a tune-up, but a newer engine won't show anything.

Man oh man! I want those radioactive sparkplugs to go with my hydrogen generator. Wouldn't that be da bomb! ;)

-mort

Small piston aircraft have dual sparkplug systems. Part of the warm up and check procedure is to run off one side then the other to check for fouled or faulty plugs or a bad magneto. Normally you run off both and you can usually feel/hear that they get more power from the same amount of fuel running on both sparkplug systems. So a hotter and fatter spark will play a roll. Like I said how much is debatable.

Any gains you see are not going to be from more of the fuel being burned but more so from how fast the fuel ignites and how fast the flame spread happens, that is part of the idea of indexing your spark plugs is that the spark is then facing the incoming fuel/air and flame spread happens faster, dual spark plugs work the same way, igniting the fuel at two points instead of one, the same amount of fuel is burning but it's burning faster, creating more pressure right away.

The only scientific study I can find is from 1931

http://aerade.cranfield.ac.uk/ara/19...report-359.pdf

Note: They won't be pinned down in there opinion on how it applies to a real engine.