Piston plug?

[orlin steven jared]

> >On the topic of spark plugs... has anyone seen the info on the new Saab 
> >plug. Engineers replaced the standard plug with a single isolated 
> >electrode then built up a special piston with a peak in the middle. The 
> >peak acts as the ground, causing a spark to jump across the combustion 
> >chamber. By changing timing they can change the effective plug gap as 
> >well. Sounds like the best plug to date.
> 
> How do they go about changing the timing _without_ changing the gap?
> I would imagine 40 degrees of advance would need a pretty hefty voltage
> to make the spark jump over to the piston.
> 
> And what happens when the time is up for a plug change?
> "OK. That'll be four plugs, four pistons, and then a full
>  engine teardown to change them. 'Have your wallet ready?"
> 
> Was this invented about 16 days ago :-)

This is a common idea, but it has many flaws, as you pointed out some
above.  Gap consistency is obviously the big one, since it will be
continually varying depending on the timing advance of the engine.
Just guessing, but I think this would cause a lot of variation in
engine emissions.

Especially since you would need a monster ignition system, capable of
sending a spark across a very wide gap during lean conditions.  
Otherwise you would have lots of backfiring.

But anyway, this brings up another question.  How do you insure that
the spark jumps to the piston anyways, instead of the side of the
combustion chamber where the plug inserts?

I ,also, don't see it happening.

Steve