Posted: Mon Jun 22, 2009 8:11 pm
I think this talk of certain substances should stop here. It will do no good for the forum, and although you may not realize it, you put yourselves in danger by even mentioning your knowledge of it over such easily intercepted channels. I know someone who suffered a very unpleasant fate because he said something he shouldn't have, and I'd hate to see that happen to anyone here. Whoever posted about themselves having experience with flash powder, I strongly advise you edit out that little remark.
Now, onto the actual topic, which, the careful observer will notice, never implied anything at all about illegal matters (regardless of the rather poorly chosen username):
The usefulness of any particular ignition system depends on the rest of the apparatus - if it takes an hour to reload and you stand 50m away to fire it, a system that takes up a lot of space (such as a capacitor discharging through an ignition coil), or even one that requires a manual reset of the spark gap (burning / exploding wire setup with high current, low voltage), is a fine choice. If your cannon is handheld and designed for easy use, something more compact is in order. The difficulty in doing so depends on your skill level and confidence with electrical builds.
-A flint-based lantern sparker is the easiest possible option, but often difficult to obtain. You could likely rig one up yourself with the right tooling and mechanical skills.
-If you live in the States, "stunguns" (which are insufficient for stunning and have no relationship to guns) make a great ignition system until they burn out (this occurs after anything from 5 seconds to several years of intermittent use, depending on the quality).
-If you're not in the States, a simple stungun design can be replicated with capacitors, a step up circuit, low voltage power supply (battery), and a miniature pulse transformer (go to 4hv, but read before you post)
-Size constraints permitting, a camera flash capacitor discharging through a car ignition coil is simple, effective, and made with readily available parts (see SpudWiki).
-A flyback-based Mazilli driver circuit (again, see 4hv) is a good choice if you're feeling ambitious, as it can be built compact and runs on a DC source)
Although it is tempting to think otherwise, a bigger spark really doesn't mean a more reliable ignition. One of my acquaintances did a test to that effect, using a propane/air mix that was just barely beyond the ability of an ignition coil based circuit to ignite it. He tried camera capacitors and steel wool, then moved on to high current arcs, and eventually up to a 500J pulse capacitor discharging through aluminum foil, which ablated rapidly and produced a plasma cloud that filled the entire chamber. This spark was comparable to a small blasting cap in total energy released, and powerful enough to momentarily raise the chamber pressure by a few psi, but still insufficient to ignite the just-barely-overfueled mix.
This should serve as more concrete evidence of the conventional wisdom here saying that "a spark is a spark is a spark" - if a 0.1J spark cannot ignite the mix, it is unlikely that any other spark / arc / 10000 degree plasma cloud filling the entire chamber will ignite the mix. The plasma cloud will improve the burn if the mix is ignitable, but it will likely not aid in actually igniting the mix unless you have so much pulsed power as to make the combustion itself superficial.
If your combustion launcher is unreliable, improve the fuel metering, increase the number of ignition points, and use a fan to mix the fuel more thoroughly.
Now, onto the actual topic, which, the careful observer will notice, never implied anything at all about illegal matters (regardless of the rather poorly chosen username):
The usefulness of any particular ignition system depends on the rest of the apparatus - if it takes an hour to reload and you stand 50m away to fire it, a system that takes up a lot of space (such as a capacitor discharging through an ignition coil), or even one that requires a manual reset of the spark gap (burning / exploding wire setup with high current, low voltage), is a fine choice. If your cannon is handheld and designed for easy use, something more compact is in order. The difficulty in doing so depends on your skill level and confidence with electrical builds.
-A flint-based lantern sparker is the easiest possible option, but often difficult to obtain. You could likely rig one up yourself with the right tooling and mechanical skills.
-If you live in the States, "stunguns" (which are insufficient for stunning and have no relationship to guns) make a great ignition system until they burn out (this occurs after anything from 5 seconds to several years of intermittent use, depending on the quality).
-If you're not in the States, a simple stungun design can be replicated with capacitors, a step up circuit, low voltage power supply (battery), and a miniature pulse transformer (go to 4hv, but read before you post)
-Size constraints permitting, a camera flash capacitor discharging through a car ignition coil is simple, effective, and made with readily available parts (see SpudWiki).
-A flyback-based Mazilli driver circuit (again, see 4hv) is a good choice if you're feeling ambitious, as it can be built compact and runs on a DC source)
Although it is tempting to think otherwise, a bigger spark really doesn't mean a more reliable ignition. One of my acquaintances did a test to that effect, using a propane/air mix that was just barely beyond the ability of an ignition coil based circuit to ignite it. He tried camera capacitors and steel wool, then moved on to high current arcs, and eventually up to a 500J pulse capacitor discharging through aluminum foil, which ablated rapidly and produced a plasma cloud that filled the entire chamber. This spark was comparable to a small blasting cap in total energy released, and powerful enough to momentarily raise the chamber pressure by a few psi, but still insufficient to ignite the just-barely-overfueled mix.
This should serve as more concrete evidence of the conventional wisdom here saying that "a spark is a spark is a spark" - if a 0.1J spark cannot ignite the mix, it is unlikely that any other spark / arc / 10000 degree plasma cloud filling the entire chamber will ignite the mix. The plasma cloud will improve the burn if the mix is ignitable, but it will likely not aid in actually igniting the mix unless you have so much pulsed power as to make the combustion itself superficial.
If your combustion launcher is unreliable, improve the fuel metering, increase the number of ignition points, and use a fan to mix the fuel more thoroughly.