Alright, "Advanced Combustion?": The best ignitio

[biggsauce]

I am building what I would consider an "advanced" combustion cannon and I am debating my ignition method. This will be my fourth combustion, and for now, I am planning to use the standard bbq "clicker deal."

After spending an afternoon browsing the combustion showcase, I saw a few different ignition methods including stungun, camera flash, bbq igniter(both "manual" and battery powered), flint striker, and even a bug zapper ignition. Jeez.

I've never had trouble with my little bbq rigs, but I see people swear by these stunguns and such because of their reliability. Anyone had one go out on them? do they wear out? If I don't use a stungun, is it still an "advanced" combustion? (With the evolution of this "hobby," many new terms have come out, largely without specific definitions.)

What positive and negative experiences have yall had with these various methods? (I've been looking at stunguns at the gunshows for awhile, but can't seem to quite justify spending the money on that when I've pulled ignitors off of garbage bbq pits for free.)

[Ragnarok]

If I don't use a stungun, is it still an "advanced" combustion? (With the evolution of this "hobby," many new terms have come out, largely without specific definitions.)

Usually, the defining characteristics of an advanced combustion are a chamber fan, metered fuel and some thought paid to an efficent C:B ratio.

Some improvement in ignition is nice but not essential. Many advanced combustions have just a BBQ igniter and a single spark gap.
A stun gun might make a little difference to performance, but the real advantage of a stun gun is the ability to re-spark very fast.

[psycix]

A stun gun might make a little difference to performance, but the real advantage of a stun gun is the ability to re-spark very fast.

Stratch that "little difference", make it "no difference".
And for the real advantage, I think this lies down at the point that it is a reliable ignition (works every time until battery is depleted) wich jumps a big distance (good for multigaps)

[starman]

I agree with psycix...stun guns are good for multiple gaps, which is definitely a performance enhancer if they are placed optimally. They also provide a hotter spark for use in a hybrid chamber where gaps have to be smaller and fewer.

Also, the BBQ ignitors tend to wear out after a while...either the spring or the piezo chip finally breaks.

[biggsauce]

Ah alright, that makes sense. I figured there was some concern about these things wearing out.

I've read a little on how piezo ignitors and I'm still pretty uncertain as to how they work. So theres a piece of electrically charged ceramic that gives off electricity when hit? Is that really it?

[jrrdw]

Ah alright, that makes sense.

I've read a little on how piezo ignitors and I'm still pretty uncertain as to how they work. So theres a piece of electrically charged ceramic that gives off electricity when hit? Is that really it?

No, there is a piece of ceramic and a piece of quartz crystal inside. When they hit together the crystal gives off the electric charge that the surrounding metal depletes it to a attached wire that carries it to the gap where it discharges across the gap.

You can look it up in the Wiki.

[biggsauce]

I forget we have the wiki...
thanks

[jimmy101]

Actually, a piezo has either a quartz or ceramic element.

Pressure on the element distorts the element and creates a voltage.
Piezo also work backwards, applying a voltage to the element distorts the element.

A "piezo" speaker is simply a thin piezo element that vibrates in response to an AC signal. A "piezo" microphone creates a voltage in response to the pressure fluctuations caused by sound waves.

In a BBQ sparker the element is long and has a relatively low surface area. A small distortion along the long axis generates the high voltage.

[jrrdw]

Here is a link to a wikipedia artical about it.

jimmy101, could the hammer that is stricking the quartz be made from ceramic???

[joestue]

It has to be ceramic, for the same reason that the white ceramic of a spark plug can shatter a tempered plate glass window, when a 2 pound sledge hammer can't. The instantaneous pressure is horrendous between two pieces of ceramic.

[jimmy101]

Here is a link to a wikipedia artical about it.

jimmy101, could the hammer that is stricking the quartz be made from ceramic???

Yep. The hammer could be made of anything that'll withstand the force. I would think that steel would be the simplest and cheapest choice of material.

The quartz vs. ceramic comes from the fact that both are piezoelectric and either can be used. Ceramic is fairly cheap and can be made into shapes that are difficult with quartz.

For a piezo speaker or microphone you want a faily thin material with a large surface area. For that, a ceramic material is much easier to make and it'll take the forces much better than a quartz crystal.

For a peizo sparker, the hammer has about the same surface area as the piezoelectric. IIRC, for a typical piezo from a BBQ lighter, the piezo surface area is perhaps 1/8" x 1/8" and perhaps 1/2" long.

[biggsauce]

So so this piezo effect diminish as the size of the crystal grows? Why don't we see, say a 5lb piezo stungun? (you know what I mean) Could this be applied to larger scale ignition system? Possibly something with much more power?

I guess the ceramic/crystal material isn't too easy to come by, but lets say you could get your hands on a 5lb hunk of that material and hit it with a hammer? Danger Will Robinson?

[mark.f]

I don't think just hitting a chunk of crystal with a hammer will do much save breaking the crystal.

I'd say if you're choosing between a stungun and a BBQ igniter, go with the BBQ igniter. You can get an upwards of three gaps if they're spaced right, and they're pretty damn reliable. The stungun is more expensive and just unnecessary if you are using metered propane and a chamber fan (any spark will work).

If you're interested in building your own sparker, use some of the camera flash methods floating around on this site. The simplest method I've seen is to use the flash tube as a "switch" to dump the capacitor into and ignition coil. You could replace the flash tube with a good mechanical switch or a solid-state device also.

[jimmy101]

So so this piezo effect diminish as the size of the crystal grows? Why don't we see, say a 5lb piezo stungun? (you know what I mean) Could this be applied to larger scale ignition system? Possibly something with much more power?

I guess the ceramic/crystal material isn't too easy to come by, but lets say you could get your hands on a 5lb hunk of that material and hit it with a hammer? Danger Will Robinson?

I'm not aware of any significant limitation to the size of the crystal/ceramic (except cost of course).

A long and thin crystal, struck along it's long axis, will give high voltage and low current. A short and fat crystal, when hit with the same force, will give lower voltage but higher current. Piezo ignitors are of the first type, piezo speakers/microphones are of the second type.

"Power" is really not an issue with piezo's used to ignite a propane + air. It takes less than a millijoule of energy (in a sufficiently small volume) to ignite the fuel. Tapping on the chamber with you finger probably puts a couple mJ of energy into the chamber. That would be more than enough energy to ignite the fuel, except the energy is spread over too large a volume.

For a spudgun ignition system you would prbably want to either hit the crystal a bit harder to get a higher voltage, or use a longer crystal and swap some of the current into a higher voltage. A better (more reliable, longer lived) hammer mechanism would probably be nice as well.

I wonder if you could run the output from a piezo through say a 1:2 home-rolled transfomer and swap current for a higher voltage? Might be possible to get a generic (ie., cheap) piezo to work better in a high mix hybrid.

[psycix]

I guess the ceramic/crystal material isn't too easy to come by, but lets say you could get your hands on a 5lb hunk of that material and hit it with a hammer? Danger Will Robinson?

Throw that big chunk of piezo from the empire state building, when it hits the ground theres one hell of a lightning strike.