Ignition with a disposable camera flash system

Blog Picture: 

While waiting for a new Spark Gap Igniter to be delivered to replace the one that failed during the previous test, I tested yesterday evening ignition with a modified 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.

Comments

ryan.pulkrabek's picture

This is really nice to see and read about. Good work. I like this system of ignition much more than the spark gap igniter approach. It is cheaper and easier to source.

I am interested in trying to replicate this approach. I tried to label the components that are in the picture. Am I seeing them correctly?

 

Damien's picture

You did label correctly - simply dismantle a disposable camera, you'll see the capacitor+PCB+battery set.

Regarding the switch, it was recommended to me to use a high voltage capable one as the capacitor churns out a pretty high one (in the 300V range from what I have found).

Hello,

I suggested using a disposable camera after looking at this innocent video:

http://www.youtube.com/watch?v=W_Qe7JyFyUo

It's nice to see the idea develop!

73 de F4GRX

ryan.pulkrabek's picture

It's a good idea, and thank you for suggesting it. Hopefully it works for us in our rocket. Keep the ideas coming if you find them :)

Damien's picture

Last Tuesday I improved the ignition system circuit, with a single switch to charge the capacitor and to unload the high voltage.

It's still messy, but it worked 5 or 6 times in a row to set off the steel wool. At least we can now be confident that it will work when we need it.

 

ryan.pulkrabek's picture

Great that you were able to improve the ignition! I would like to replicate this at some point. Would you mind updating the wiki with this information?

Damien's picture

Sure, I will update the wiki with my findings in the coming weeks.