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Re: spark plugs

To: Matt Pringle <>
Subject: Re: spark plugs
From: Bill Saidel <>
Date: Wed, 04 Aug 1999 10:16:27 -0400
    Lemmeee second Matt's note with lots of qualifications. He is pointing
out that in a parallel circuit (which is what multi-path plugs represent in
his note), current flows through every path to ground. Right.
    However, the issue is not a constant source of current (and read
constant as equal to not instantaneous to make sense of his water analogy
which is also good). Rather, it is an "instantaneous" source and an
"instantaneous" response through a plug when a spark is generated. [Plugs
discharge once per compression, no?]. So the situation is, for
multi-electrode or split electrode plugs, not quite the classic parallel
circuit, but which electrode fires the explosion first. 
        The real issue lay with a focus on who is doing work. In the case of
electrical circuits, the individual elements are doing work. In the case of
a spark plug and cylinder in a real car, it is the gaseous explosion that
is forcing the cylinder to do the work. From the point of view of the
cylinder, two explosions, one from each side of the electrode but delayed
by a finite but small amount may even hinder or decrement work. So to model
a plug, you should consider its Thevenin equivalent which reduces to one

        Now, if one of you engineers knows whether the discharge of one side of
the electrode promotes the nearly simultaneous discharge of the other, or,
does the resistance of one side of the electrode go close to zero during
discharge so the firing side becomes the sole source of the spark, I'd like
to know. 

        Seems to me if the geometry of the electrodes and the timing is correct,
it doesn't matter which electrode fires, just that one does at the
appropriate time.



 ( At 09:38 AM 8/4/1999 -0400, you wrote:
>Ummm, I think I have to disagree here.
>I've heard this pseudo-theory more times than I care to remember.
>No where in electrical theory (or practice) does electricity seek the
>path of least resistance, this is an old wives tale.  If I have several
>parallel paths of electrical flow, certainly more current will flow
>through the path with the least resistance but electricity will most
>definately flow through all paths.
>As you state, it is just like water, if you flush the toilet, have the
>shower on and turn on the sink faucet, water will flow through all of
>them but in differing amounts.
>> There's lots of what I term "gimmick" plugs out now with multiple
>> be it 2,3,or4.. The only problem with these is that basic electrical theory
>> states that electricity, like water, seeks the path of least resistance.
>> means that it's likely that what will happen with these multi-path plugs is
>> that only one conducter is ever actually working, until it wears enough
>> the path to the next one is now easier, ad infinitum. (unless by some freak
>> chance each electrode was exactly the same distance and electrical
>> as the next)
Dr. Bill Saidel 
Assoc. Prof.                      Vocal phone   (609) 225-6336
Department of Biology             FAX  (609) 225-6312
Science Building                  email:
315 Penn St.
Rutgers, the State University of New Jersey
Camden, NJ 08102 -1411

"Between the approximation of the idea and the precision
of reality, there is a small gap of the unimaginable."
Milan Kundera - "The Unbearable Lightness of Being"

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