On Fri, 14 Nov 2003, David Beierl wrote:

> >of the more compact methods is to put the contacts inside a sealed chamber
> >which is evacuated to a high vaccuum.  No air means nothing to ionize
> >to carry the arc current.
>
> Ah ha!  And you don't get a metal arc?  Are the contacts tungsten or some such?

I'm not sure what they make the contacts out of.  But there's a lot less
vaporized metal available to make an arc than there is air in a normal
breaker. ;)

> But getting back to IC ignition, how much of that is arc?  Does it really
> become the low-resistance point of the system?

It wouldn't surprise me.  I'd expect the resistance of a spark plug arc --
we're talking a fraction of an inch here, remember -- to be on the order
of a few ohms once it's struck.  People who make cool but dangerous
high-energy devices like "quarter shrinkers" sometimes use spark gaps as
high-current, high-voltage switches for this reason.  It's cheaper than an
SCR stack. ;)

David Brodbeck, N8SRE
'82 Diesel Westfalia
'94 Honda Civic Si -- For Sale
'86 Volvo 240DL wagon