@quiman
Congratulations, You are one of very few people to get this far
It's interesting that this effect(electrostatic cooling) is almost completely absent in the scientific literature but has been around for a very long time. The most noteable person to utilize this effect was Victor Schauberger some 80 years ago, many people equate Schauberger with water and the vortex but this was only a small part of his work. Victor stated he could produce 2 million volts potential from a single drop of water using capilliary tubes and a small suction source! and the resultant "cold expansion" could produce a large temperature drop. In the right context this cold expansion could also produce a perfect vacuum to power his devices . In our world we equate heat with expansion and cold with contraction but this seems to be a bit of an illusion as heat and cold are not "something" they are a condition of "something". If only heat expands and only cold contracts then why is our cold upper atmosphere at a low pressure? It should be very dense if it has supposedly contracted. We could also say radiating energy is expansive relative to the source and contractive relative to its target. In any case if heat is not produced I think it is safe to assume the forces involved are electrostatic in nature, as everything is.

@qiman
There are things happening in the spark which we don't fully understand. I was thinking, maybe the ir light from the ir temperature meter is being absorbed or manipulated or whatever, therefore it isn't showing the correct temperature. Maybe a low-tech temp-meter should be used, just to be sure it is really dropping.
Just a thought.

(I see tinu asked the same)

I will simply say if (baring a Radiant Event from unknown process of huge purportions) a 3 coil transformer hand wound over a nail with nothing but a large limited DC current flowing through 2 of the coils (7 turn and 13 turn)  encasing the 3rd coil (5 turn uninsulated!!!!!)  feeding the HV pulse from the original coil to the plug.......If this can provide a 200X boost in output current through the spark gap, the shifting of timing past TDC and this huge flash,  I'll eat that nail........I have also eaten crow in the past! 

Ben - maybe you should get prepared to eat that nail ...

As I understand it - what is required (after the initial HV low current spark) is a lower voltage high current discharge.  We don't actually know what voltage is needed for this secondary discharge - people are blowing up inverters because inverters are available off the shelf - but we haven't proved we need the voltage to be that high.  Some, including myself, have speculated about connected the 12V directly to the spark plug for the high current discharge.  (Remember - Graneau have given good science that it is Amps that blows the water apart - so at this stage in the process, unnessary voltage multiplication at the expense of current is counter-productive).

So very likely, a rudimentary coil of few turns is exactly what we need ... perhaps he is using multiple discharges at lower and lower volts (with higher and higher current) ...

Don't sneeze at this simple coil arrangement.  In this thread we have no idea who the real information or the real disinformation is coming from.  These coils are so easy a child could build - so try them!

Electrostatic cooling ... wow.  I know Tinu made me out to be a bit of a fool, and that's fair enough.  I don't suppose to know everything there is to be known about water and how it works.  So whatever the right terminology - I am convinced the best energy source is in that low temperature liberation of whatever the hell it's going to be called once mainstream science starts to acknowledge it's existence...

I would like to point out one simple fact:

I can make this effect with a variac or inverter DISCONNECTED/ISOLATED (both terminals isolated) from the capacitor so this rules out 100% for a fact that I am getting any extra high current surge from the power supply.

Some want to believe it can come from a capacitor...(once it is discharged).

What S1R shows with some inverter touching the plug off and on through a relay and then ignition coil off/on...whatever he is showing is NOT the same method as Luc has found. So some are automatically thinking that there is some surge from the power supply to make this spark based on Luc's circuit because of some crossed idea that it is supposed to be the same thing?

Also, has anyone bothered to scope the function of the diode?

I see something that seems to almost be deliberately IGNORED here. My power supply is 100% separated from the capacitor on BOTH terminals when the capacitor is discharged into the spark plug. That means 100% as an undeniable FACT, there is no current surge from my variac or inverter going to the coil when the HV pulse leaves the ignition coil.

So that leaves the capacitor as the only thing connected to the circuit as far as input. Once the capacitor is discharged, there isn't enough to provide any current surge! With a 3uf capacitor, that is 0.0384 joules of work possible (with no losses) if it is charged to 160volts. That is LESS THAN 0.04 watt seconds worth of energy...and if using a 3uf cap, once it is discharged and claiming that there is some current surge from the cap..again AFTER it is discharged will have some current surge that assists this spark...even with a 47uf cap at 160v, that is 0.6 watt seconds or 0.6 joules...and AFTER discharge there is enough for some mysterious current surge??? LOL Well, again...is this DISINFORMATION...there might be enough energy left in the cap AFTER discharge to may raise 1 hair on a flea's leg, but to assist in some robust spark on a plug like we're witnessing???

1. Why do I get the effect without any power supply connected to my cap?
2. AFTER the cap is discharged, why do I get the effect still and do you honestly think there is enough in the cap to give some current surge to cause this effect?
3. HOW DOES A DIODE WORK?
4. Think about VOLTAGE POTENTIAL..........where there is any kind of voltage...that potential is available EVERYWHERE instantaneously wherever it it is in contact with some kind of conductivity as long as it is not blocked. When the arc is happening, the HV potential is available at the exit of the HV diode...what does that tell you?