Re: Spark Plug query

Mark Olson wrote:
Chris N Deuchar wrote:
....
Being an electronic engineer I know at least some of the foregoing is hogwash - but am not sure how much is true of the plug architecture. *Is* there perhaps an internal resistor on 'R' types or what?


Yes. The function of the resistor is to reduce peak current, hence EMI.

That's what I'd always heard too, resistors prevent radio interference. And then, in A&P school, I learned they prevent capacitive afterfire.

The shielding around the ignition wires reduces EMI. The center conductor and the shielding, however, effectively make up a capacitor. As the plug fires, the capacitor discharges, prolonging the spark across the electrodes and needlessly shortening plug life. The resistor lets a high energy spark occur and quickly cut off.

So that's the story out of the FAA-approved powerplant textbook.
.

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