In the development of their SDS crank-trigger ignition system the guys up here
at Racetech built a cylinder with an air fitting, a spark plug hole, and a Lexan
window. They found that at higher pressures, the stock coils would barely fire
the spark plug, while switching to any of a number of different 'high-energy'
coils gave good spark even at high pressure / high RPM. Bob, how does the
dielectric breakdown potential of air go with pressure and temp? If it is
linear, and about 30 kV / cm at standard temperature and pressure, then at 100
psi (call it 7 bar) you will need about 21000 V to fire across a 1 mm (0.039")
gap.
If you have one of the really powerful ignition systems, you also have to be
extra careful about the condition of the inside of the distributor cap, wires,
plugs, etc., since that bolt of blue you're trying to dump down a particular
plug wire can skip over to the next terminal without too much trouble if it
finds any extra impedance in the intended path.
Theo Smit
tsmit@novatel.ca
B382002705
> -----Original Message-----
> From: Bob Palmer [SMTP:rpalmer@ames.ucsd.edu]
> Sent: Thursday, November 12, 1998 10:15 AM
> To: Steve Laifman; Chris Richards
> Cc: Joe Hankins; James E. Pickard; Tigers
> Subject: Re: Electronic ignition
>
> Steve, Chris,
>
> To really discuss this subject rationally, we need to recognize that
> "voltage" is not a unit of energy. So comparisons of various components on
> the basis of voltage is very misleading. To start with, all coils generate
> enough voltage to arc across the spark plug gap, at least up to about
> 4-5000 rpm; and this voltage is way below 10,000 volts. So the open-circuit
> maximum voltage is really a moot point. The parameters of the discharge we
[Theo Smit] <clip>
> Robert L. Palmer
> Dept. of AMES, Univ. of Calif., San Diego
> rpalmer@ames.ucsd.edu
> rpalmer@cts.com
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