just wondering

[iamthewalrus]

im jsut wondering, will u get the same preformance from a bbq spark as a stungun spark?? ik the snug gun is higher voltage but does that ignite the fuel any better then a bbq sparker?

[Cole]

I think a stun gun due to the higher voltage will light more dense fuel and if you have more than 1 spark in your chamber then it lights more fuel at once, and a bbq igniter gives a weaker spark and you can only have one spark in the chamber with one bbq igniter.

[spudshot]

you can jump a larger gap so it has more chance of igniting, and more chance of igniting more fuel. the spark is also hotter.

[iamthewalrus]

ok, thanks. but i got two sparks with my bbq. but they prolly wernt very hot

[spudshot]

yeah, you can jump multiple gaps with about any ignition, i've been using about 20 sparks with my circuit board ignition (the little copper circles make good electrodes) with a normal bbq ignitor, if i used a stungun i would be able to use a much larger sparkstrip and have many more ignition points, pretty much as long as your spark gap isnt longer that your test electrodes (on the stungun) your stungun wont die quickly

[taterjim]

It seems to me that if you get combustion by whatever method ,and I have 4 different types , most of the fuel is burned ,and sometimes you can get a small second combustion from left over gasses. The better ignition sources will get combustion a higher percentage of the time however.

[longshot1068]

That is another reason to use a fan in the chamber to mix the fuel, it will provide a much more efficient burn. With a higher voltage ignition source, you will be able to achieve not only more sparks but also bigger sparks- which will begin burning the fuel at many more spots at once, effectively creating multiple instances of simultaneous combustion. if you get all the fuel to ignite at the same time it will yield substantially better results by releasing all of the energy contained by the fuel- which means that all of the energy transfers to the ammo at one time. I know, BLAH BLAH BLAH.

[boilingleadbath]

The effect of multiple spark gaps/higher current ignition devices is disputed, partly because there don't seem to matter much.

[FiveseveN]

"Disputed" is the perfect word for it.
I had written a pretty long post on this matter, but a freak accident deleted it, so I'll have to be more succinct.
The keyword is MOMENTUM! We can compare a combustion cannon to a basic collision system. The factors in this system are:

- mass (of the projectile, since the hot gas has little and almost constant mass)
- velocity (of the ignited gas. This depends on mix ration, nature of fuel, temperature, etc.)
- friction (of the projectile to the barrel)

This is why I always praise APFSDS projectiles. They are perfect for large calibers (above .50), IMO.

After a little mind-math fiddling with the above factors, we can draw some basic facts:

- heavy projectiles (ice, concrete etc.) achieve top velocity with slow-burning propellants
- heavy-friction projectiles (spuds) also achieve top velocity with slow-burning propellants
- light projectiles ("missiles", APFSDS) achieve top velocity with fast-burning propellants (aceylene, H2+O2 and the like)

We're talking about a high-quality rig, so leaking around the projectile is ZERO and "acetylene" and "PVC" never belong in the same sentence!

By looking at the above, your basic tips would be:
- the heavier the projectile, the slower combustion you want (one spark at the end of the chamber + heavy fuel)
- there must be as little friction as possible between the projectile and the barrel, yet there mustn't be any leaking between them. I'm sure everyone figured that one out by now. I suggest using petrolium jelly or leaving the cut spud in hot water at 70 degrees C for a couple of minutes (will harden the starch, making it not stick to the barrel and jelly-like).
Combustion speed (well) above Mach 1 solves the friction problem, but raises others.

Feel free to correct me and I'm sorry for any errors.

[longshot1068]

well if multiple sparks dont make a difference, why do they work so well in automotive engines? I realise that the fuel/air mix is compressed in an engine but that just makes it easier to burn in the first place. If they made little difference people wouldnt buy or use them, and manufacturers wouldnt produce MSI systems or engines with multi spark plugs per cylinder. even if the gain is minimal, it is still a gain.

[boilingleadbath]

"The key word is momentum"
Except it's not. Energy remains fairly constant over projectile mass.
Someone with a combustion cannon and a cronometer should do some tests on that.

[FiveseveN]

Energy remains fairly constant over projectile mass.

And how does that contradict what I said? I was only talking about velocity, not energy.
I may be wrong, though. Somebody should definately run some tests.

[WOW!!]

With the stungun you can have some many sparks as with the BBQ 1, you can only have 1 if you are lucky 2, you can make spark strips chamber shorts and all different kinds of stuff with a stungun, but if you are just starting out then go with the BBQ one and then upgrade lateron, and with the hybrids dont even try to use a bbq iqnitor you cant cause the fuel is to dense.
hope that helps



Josh

[Shrimphead]

Are you sure about not being able to use a bbq on a hyrid? I've never heard that before. I just always assumed that people who have enough money and experience to build a hybrid are gonna go with a stun gun over the bbq.

[boilingleadbath]

I have no experience with ignition in a hybrid, but the maxium spark length you'll be able to get with a 3x mix would be about... .25-.3", so it should work, although reliability might suffer.
(based on spark length being inversely porportional to gas density and my experiences with BBQ peizo-electric voltage sources)