Ignition only

[Chris Conlon]

At 08:41 AM 11/9/00 -0700, Programmer wrote:

>>The same current flows across both spark gaps - this must be the case
>>unless we're losing or gaining electrons somewhere. The high voltage 
>
>
>Measure it on an ignition scope sometime...it's not the same kV
>required to fire the waste side as it is the power side. That's
>correct about the gap to "some" degree--other than the rotor to
>tower gap and the plug gap is always on the power side. Not so
>with DIS. The power side on DIS may be 8-10 kV, where
>the waste spark side is 1-2kV (measured).

He's talking current, and is correct. You're talking voltage, and I
presume you're correct too. The current should (in any likely case)
be equal, the voltages may be very different.



At 10:21 AM 11/9/00 -0600, don.broadus at exeloncorp.com wrote:

>would the difference in the kV voltage on the waste spark side have to do
>with the lower cylinder pressure  or  possibly ionized exhaust products. ?
>Just wondering

The breakover voltage (the peak just before the spark fires) depends
mainly on the gas density in the cylinder, and (in the case of the
wasted spark) the fact that the gases are fairly ionized. (This
lowers the breakover voltage). High temperature also lowers breakover
voltage somewhat. The gap voltage during the spark event depends
mainly on ion loss, either as ions drift out of the gap, or as non
ionized gases drift into the gap. If everything is uniformly ionized,
current flows easily, the gap voltage is low and little power is
dissipated in this half of the circuit. If there is a lot of
unionized gas, current flows less easily, gap voltage is high, and
more power is dissipated in this half of the circuit. This is a
*good* thing, because only power *dissipated* in the spark gap can
help ignite things.


One difference I didn't see mentioned is that waste spark systems
fire one plug "backwards". (Normally the hot center electrode is
negative, since it's electrons being emitted that actually start
things off, as in vaccum tubes.) This probably means that the plug
gap in those cylinders cannot be as large as in a "forward"
cylinder, but I'm not sure if this is a meaningful difference or
not.


   Chris C.

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