There are high performance electronic ignitions available that spark
     considerably more than twice for each power stroke (I don't know what
     the upper limit is but I've read of ones that fire at least 4-6
     times). To be effective they must use multiple ignition coils since
     the coil needs a finite amount of time to build up enough flux in the
     coil to generate a spark when dumped. This is different than the
     multi-coil setups in modern engines.

     The modern systems that use one coil for each 2 cylinders are used to
     avoid the need for a distributor, and have longer to build up the flux
     than the multiple spark units. They rely on the fact the when a given
     cylinder is ready for the power stroke (and spark), the opposing
     cylinder is ready for the intake stroke, and the spark going through
     the plug in this cylinder has no effect. It's kind of like those
     built-in pushbutton BBQ ignitors. One end of the peizo goes to the
     main burner spark gap, and the other end of the peizo goes to the side
     burner gap. Both gaps always spark when you push the button (at least,
     that is what is SUPPOSED to happen), but only the one with gas coming
     out has any effect.

     Incidentally, there is a new technique that seems to work even better
     than multiple sparks. In this system the cylinder is designed so that
     at the time of the spark, a sizeable air stream is flowing past the
     plug (perpendicular), which stretches the spark shape out to the side
     in a long arc. Much more gasoline than normal comes into contact with
     the spark this way. Initial test show considerably higher power,
     better fuel consumption, and especially important in these eco-nazi
     days, significantly lower emissions.


     CIAO - Martin.


______________________________ Reply Separator _________________________________
Subject: Re: Spark Advance Help OT
Author:  pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU> at
Internet
Date:    6/12/98 12:07 PM


I believe that those engines that spark twice really only spark once.   The
coils
just have two outputs (one spark plug on each end of the secondary
windings) so each
trigger fires two plugs simultaneously.

Problem with this is that one spark plug the center electrode is positively
charged, the other
negative.  Forget which way is preferred, but one of the plugs wears out
faster in the dual
firing/single trigger setup.

Dave
>The other problem (more serious imho) is more wear on the HV section (coil,
>etc).  If you're running 6000 RPM, that's 12000 sparks/minute on a 'normal'
>firing setup.  24000/60 = 800 sparks/second.  Not many non-racing ignition
>systems can handle that speed AND deliver a hot spark.
>
>