Spark time
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I'm using the definition "spark time" as a measurement on how long time it has been a spark.
Ignition time is measured between top dead centre (TDC) and when the ignition starts.
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This test is showing that it is possible to measure how long time it has been a spark.
Too short spark time will not ignite the fuel/air mixture and you will have a misfire.
On the spark plug you will see it as a thin spark.
If I short the high voltage side (spark plug side) of the ignition coil to ground that will change the inductance of the ignition coil to a lower value compare to a non-shorten ignition coil.
That is the same as if it has been a spark; the electrons in the spark create a low resistance.
The frequency is now 10kHz created by the LC circuit that I mentioned before.
A change of the inductance value from a high value to a low will change the frequency from low to high. That is the same as for the capacitor, a change from a high capacitor value to a low will change the frequency from low to high.
An ignition coil that has no shortage of the high voltage side (no spark) has a higher inductance and will generate a lower frequency.
The frequency is now 2.4kHz.
With this method it is possible to measure how long time it has been a spark.
In this case the time is 2.3ms.
The flat part between the oscillations is created because the initial spark (AC oscillations) has created plasma of electrons that is floating between the electrodes of the spark plug.
When the flow of electrons stops the load of the ignition coil is removed a change of inductance and it generates a low frequency oscillation. At that time there is no spark.
The proof of the DC current flow (electrons flow) is shown in "Negative vs. positive ground systems". The polarity of the ground systems and the connection of the ignition coil will effect the spark time when the spark plug is hot.
The time it has been a spark depends on the air pressure in the cylinder of the engine.
The higher pressure the harder it is to get a spark.
The timing depends also of the gap of the spark plug.
The short pulse (white) is from a spark plug with a large gap, the green pulse is from a spark plug with a short gap.
The current out to the spark plug
This test showing the relation between the measurement at the capacitor and the actual current out to the spark plug.
The probe that was used to measure the current out to the spark plug was a probe from a stroboscope test instrument used for adjusting the timing of the ignition system.
It is hooked up on the high tension cable out to the spark plug.
This proving that the theory was right. The spark time was 2.5ms.
It is quite handy to have a probe that easy can be connected to a high tension cable for each spark plug. The fault findings in a system will be easier if there is a misfire, and also to see if there was a spark on that spark plug.