[Diy_efi] Multiple Spark Plug B & S engine

Phil Hunter diy-efi at t-n-e.com
Sun Jan 30 17:58:13 GMT 2005


[Blind Cc: to several friends]

Folks,

Somewhere in the email archives is a (dead?) link to a project putting 4 spark
plugs on a B & S engine. While cleaning up disk space I found some interesting
files in C:\windows\temporary internet files. I was able to contact the author,
one thing lead to another, and we now have an updated web page available.
diy-efi.org is a good place for it, but until Steve can make a home for it I'll
host it on my site: http://www.t-n-e.com/4plug

Besides just the "cool" factor, this project interests me for 2 reasons.
I've been playing around running a B&S on hydrogen, w/ H2 you can run very
lean mixtures, out to about 160-180:1, but such lean mixtures can be difficult
to ignite reliably, multiple plugs to the rescue...

The second reason is ion-sensing ignition.
One of the difficulties w/ it is getting the coil oscillations to die down
quickly enough after the spark is started to be able to measure the ionization
before the peak pressure point is past. This is why Capacitor Discharge is
often used, the coil is used solely as a step up transformer rather than as
an energy storage device, minimizing the oscillations.

Another technique if you have the space in the combustion chamber is to use a
second spark plug solely as a sensor, no high voltage spark, no additional
circuitry to block the H/V, and no waiting on the coil. Since hydrogen burns
up to 7 times faster than gasoline (at stoich), this may be the only technique
that will work for me. The smallest spark plugs I've found are about 5/32"
(4mm) in diameter used in miniature engine replicas. I suspicion I may have
trouble w/ their heat range being too high however, but I have a lot of "baby
steps" to take before I find out.

rgds,
philh

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