Forgive my ignorance, A/M ignition

[NoDOHC]

Correct you are, but there is only one side that matters anyway (the other side is the 'wasted' spark) so a misfire is just that, a misfire.

The air has a very high resistance until the electric field intensity exceeds the breakdown level (based on plug gap, AFR, compression ratio, charging efficiency, boost, etc.) no appreciable current will flow until the air between the electrodes is ionized. Once this happens, the resistance drops to a very low level, effectively shorting the coils out (voltage drops very low) The actual spark is then a current through the now-ionized air gap.

The problem with parallel circuits is that the dielectric strength of the spent chamber (just completing the exhaust stroke) is a lot lower than that of the compressed chamber with air and fuel in it. This means that the spark voltage will build until the field intensity exceeds the breakdown level of the lower dielectric, then that ionized gas in the air gap of the spark plug will short-circuit the coil (spark voltage goes low) while current flows through the air gap. This means that the charged chamber will never get enough voltage to the spark plug to exceed the higher dielectric strength and the charged chamber will never fire.

Wasted spark is very reliable (typically). I don't like it because it requires twice the effort (ignition events) out of each coil (while it only requires half as many coils) the charge time for the coil is half as long as it would otherwise be, this means there is not enough charge time to get a reasonable ignition energy to the air/fuel charge in the chamber at high revs.

[Pete_89T2]

Originally Posted by NoDOHC

The problem with parallel circuits is that the dielectric strength of the spent chamber (just completing the exhaust stroke) is a lot lower than that of the compressed chamber with air and fuel in it.

What data supports this? If this were true, then the odds of the the stock FC ignition system ever firing the leading plug of the *correct* rotor (i.e., the one with the compressed fuel/air charge) would be slim to none.

Originally Posted by NoDOHC

This means that the spark voltage will build until the field intensity exceeds the breakdown level of the lower dielectric, then that ionized gas in the air gap of the spark plug will short-circuit the coil (spark voltage goes low) while current flows through the air gap. This means that the charged chamber will never get enough voltage to the spark plug to exceed the higher dielectric strength and the charged chamber will never fire.

This explanation is correct, but I suspect you've got the dielectric characteristics reversed - it must be much easier to jump a spark across the gap when the medium is a compressed fuel/air charge than exhaust gases & blowby, assuming the full regime of variables as Mazda designed, otherwise our leading plugs would always misfire.

[RETed]

Circuit is not as simple as we thought...

Did a quick test of resistance on the terminals.
If the parallel circuit was as simple as above, measuring resistance across the towers should be nil - not the case.
In fact, the towers are isolated from the two coil inputs + and - (no surprise there), and there is no resistance between either tower to coil ground - kind of a surprise.
The coil outputs are isolated from every part of the coil body including from each other.

Twin, independent coil circuits wound within the coil body itself?


-Ted

[Pete_89T2]

Originally Posted by RETed

Circuit is not as simple as we thought...

Did a quick test of resistance on the terminals.
If the parallel circuit was as simple as above, measuring resistance across the towers should be nil - not the case.
In fact, the towers are isolated from the two coil inputs + and - (no surprise there), and there is no resistance between either tower to coil ground - kind of a surprise.
The coil outputs are isolated from every part of the coil body including from each other.

Twin, independent coil circuits wound within the coil body itself?


-Ted

Ok, now it's starting to make sense. By inference of Ted's measurements, the tower outputs can't be wired in parallel. I can't draw & post the circuit, so hopefully this description will make sense to everyone if you reference NoDOHC's diagram and use your imagination.

If you added a 2nd distinct coil winding to the secondary side of the transformer, and connect one leg from each of these secondary windings to a common ground through a diode (i.e., allows DC to flow in only one direction, connect "-" side of the diode to ground, "+" side to coil winding) and the remaining coil leads become your L1 & L2 tower terminals, Ted's measurements make perfect sense. In effect, we have two secondary coils driven by a common primary coil.