Dave, my take about resistance, and I may be wrong, is basically related to flow. More resistance decreases total flow. This could be applied to water, air, electricity. Too much resistance and flow is greatly diminshed.
Jerry, this does apply correctly to DC theory.
But, coil operation is in the AC theory domain and behavior is different and more complicated to explain than the DC environments.
I'd also like to hear someone explain in an easy to absorb way that us non-electrical engineers might understand better.
The dwell time and coil construction determine how much energy is stored at saturation. When the coil's power is removed, the power soaked coil begins to loose it's stored energy and develops a voltage. No current flows during this time and no amount of resistance has an effect on passed through the resistor voltage. It is only when the voltage rises far enough to create spark across the spark plug gap, that current begins to flow. Low or no resistance allows the coil's energy to dump fast at high currents. The currents contribute to spark electrode heating and wear as well as a short discharge event.
Adding resistance to the spark circuit reduces the current flow through the spark gap, slowing the coil discharge event and making it longer. This is because the stored energy is restricted from rapid discharge. The total energy is still getting used, just over a longer duration. An artifact of the added resistance, also slows the fall time of the initial pulse peak. Rapid fall times include high frequency components, which are broadcast through the unshielded ignition wires (antennas). The delayed fall time also, therefore reduces radiated electromagnetic emissions.
I've included a reference diagram below of a captured secondary voltage wave form. Clearly, it's not anything like a nice stable DC line.
C is the voltage rise in the secondary and is presented across the spark electrodes.
A is the point at which the spark channel is formed across the electrodes, where it then falls to spark maintenance levels.
B is the spark current event duration.
D is where the coils energy has depleted enough to halt the spark channel event.
Adding resistance leans/tilts/extends the slope at the fall from point A when current is flowing through the wires (EMI/RFI reduction effect). But, it also extends the duration of B as it now takes longer to deplete the stored energy in the coil.
Note the Voltage needed to begin the spark event will NOT change, as spark formation is gap and between gap atmosphere dependent. Also, the voltage to maintain the spark channel (B) will not change either, as that is what is need to maintain the ionized spark gap channel electrode bridge. However, during the spark event, the current will be lower thus contributing to longer spark electrode life due the the jump off points on the electrodes heating less. See also EDM. (Electrical Discharge Machining, removing metal with spark energy.)
Hopefully, the attachment will help with understanding. Don't know if it is easy to absorb. But AC theory is not found on the first rung of the knowledge ladder. I'm sorry I couldn't find a waveform that actually showed the spark duration extension with increased resistance. You'll have to trust me on that, I suppose. But, it's a conservation of energy, thing. And the resistors only change the rate of discharge not the quantity of discharge related to the coils' stored energy.
Cheers,
