Posted by kencombs on October 28, 2020 at 08:54:34 from (108.208.32.113):
In Reply to: spark plugs again posted by flying belgian on October 27, 2020 at 10:24:46:
My minimally educated guess at an explanation is this: As others have stated the spark jumps the gap because the high voltage present has ionized the air in the gap creating a path for the electrical arc.
the voltage must be high enough to 'knock' some electrons free in order to do that
The voltage present at the plug is determined by the ignition system and (this is key) the rate of rise. If the plug has a leakage to ground due to faulty construction or fouling some voltage will be lost before the air molecules are ionized.
Under load, most if not all engines will have a method to admit more fuel, or richen the mixture. Some of the air molecules in the arc path are replaced with fuel molecules that don't readily ionize. And, due to the added air being admitted by the throttle, there are more air molecules in the arc path, requiring higher voltage to ionize.
The mentioned leakage will drain off part of the current delaying the voltage rise.
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