Ignition with a disposable camera flash system
The modifications were simple, a few tin solders to remove the flash itself and connect the two legs of the capacitor to two wires. One of the wires was connected to a switch qualified for 250V, and another wire went from that one to almost touch the wire coming from the other capacitor leg (the space between them was less than a tenth of a millimeter). The overall effect, after the capacitor was charged, was to short circuit the capacitors legs, which generated a spark that can be seen in this video.
Once the spark generation was made reliable (I had to remake my initial soldering), I tried several ways to use that spark to generate ignition.
The first tests were performed with cotton wetted with different flamable liquids: acetone (albeit only at 25% concentration), white spirit and isopropanol. None of these lead to a flame, the only visible effect of the spark was to create a small black deposit in the cotton.
I then connected the two wires with a bit of steel wool, which ignited easily when the system was switched on. Once that was demonstrated, I extended a blend of steel wool and cotton from the steel wool linking the two wires, and it generated the ignition visible in this video (even if it is dark, the combustion is of course easily visible).
The conclusions I make of these tests:
- this system can fairly easily be made to work reliably, in comparison to the spark gap igniter: where the wires linked to the spark gap igniter have to be kept at a distance from the steel wool to avoid a short circuit, with this system the short circuit is what generates the spark. That's an easier setup to prepare within the combustion chamber than to set it up to have the correct spacing between wires and steel wool.
- it is easier and cheaper to source than the spark gap igniters. The system I used was from brand new disposable cameras I purchased from Amazon at about 5€ apiece, but I was told in the lab that this should be retrievable at no charge from any photographer shop.
Next step: test this ignition with a bit of pulsed air within a paraffin grain, in order to determine how well it behaves.
A big thanks to all those at the lab who contribruted to last night experiments through advice and/or practical help: Crafty, Guillaume, Teguest and Jnat. Not to mention the many spectators! I know I repeat myself, but the Electrolab is just a wonderful place to work on a project, with a huge knowledge database and motivation source gathered in the form of the other members.