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rapid sparks?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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rapid sparks?

Unread postAuthor: taytayswims » Sun Jun 01, 2008 10:03 pm

the type of grill ignitor im looking to get are the kind that spark 3 or 4 times a second. there is a grill down the street from my house with a free sign on it and i was wondering if it could be used if it still works because im not sure of the design of the housing unit with the sparker
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Unread postAuthor: BC Pneumatics » Sun Jun 01, 2008 10:58 pm

If the igniter was still functioning it could be salvaged and used, as long as it is they type you are looking for, and not the one click one spark piezo variety.
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Unread postAuthor: taytayswims » Sun Jun 01, 2008 11:00 pm

yea i got it and i can use it very well to my surprise i will have a post of my new cannon soon
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Unread postAuthor: psycix » Mon Jun 02, 2008 4:59 am

And what would be the function of so many sparks taytay?
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Unread postAuthor: TurboSuper » Mon Jun 02, 2008 7:04 am

More reliable ignition.
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Unread postAuthor: jimmy101 » Mon Jun 02, 2008 4:17 pm

TurboSuper wrote:More reliable ignition.

How? If it didn't ignite on the first spark then there is something seriously wrong with the gun. Better to fix the fueling / mixing problem then to try to kluge your way around it with multiple sequential sparks.
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Unread postAuthor: TurboSuper » Mon Jun 02, 2008 4:30 pm

jimmy101 wrote:
TurboSuper wrote:More reliable ignition.

How? If it didn't ignite on the first spark then there is something seriously wrong with the gun. Better to fix the fueling / mixing problem then to try to kluge your way around it with multiple sequential sparks.


Depends on the cannon. If it was a fancy-pants advanced combustion with a stochimetrically accurate fuelling system, then I'd be inclined to agree with you. However, in a spray n pray, sometimes you have to click the sparker a couple of times before it ignites, so it's better to have it "clicking" several times a second.
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Unread postAuthor: BC Pneumatics » Mon Jun 02, 2008 4:35 pm

Jimmy- There are many guns that are designed knowing full well that they cannot achieve a perfect fuel/air mixture, or even one good enough to be ignited the first time, every time. Spray and Prays, cannons without chamber fans, launchers with low resolution meters, they are all prone to the occasional poor mix, but none of them have anything seriously wrong with them. Just because it is possible to make a higher quality launcher does not mean something that is less than perfect is worthless or broken.
Just because you like to build top quality race cars, does not mean to need to talk down on everybody that is happy with their mid 90's sub compact, even if it does need a jump start every now and again.
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Unread postAuthor: psycix » Tue Jun 03, 2008 6:48 am

Multiple spark sequences still have no use.
Look:
-A good mix always ignites on the first time.
-A bad mix that is still good enough to ignite always ignites on the first time.
-A bad mix that is so bad that it cant ignite, never ignites no matter how often you spark.

As you see, you will never need a second spark.
You might say:
Ive had times where I had to spark mutiple times. But that means that OR your ignition fails and doesnt spark the first few times OR you need to wait for the fuel to mix somewhat longer and instead of clicking right away.
You should just wait a few seconds instead. (Or upgrade with a chamber fan! its really worth it!)
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Unread postAuthor: jimmy101 » Tue Jun 03, 2008 5:04 pm

Like psycix said. There is actual data that indicates that repeatedly firing the spark gap, particularly when you are talking about several firings per second, is the worst thing you can do. The gun will never ignite if it is continually sparked.

If it doesn't fire with the first spark you do not want to immediately spark it again. You want to wait for a few seconds, invert the gun, do a chicken dance, do something while you wait for the fuel to continue to mix.

Every spark consumes some fuel. Spark it enough and there isn't enough fuel in the gun to ever ignite. Spark it continually and you'll never get a combustable mix at the spark gap.

Crappy ratio, no chamber fan? The last thing you want is a sparker that fires several times a second.
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Unread postAuthor: BC Pneumatics » Wed Jun 04, 2008 1:41 pm

One cannot say a cannon will never ignite if continuous sparking is applied, just because one test proved that trying to ignite a fuel air mixture in a 27:1 chamber designed for slow diffusion once every several minutes does not work.

While these tests are certainly interesting and warrant further investigation, many spudders know that it sometimes takes a few clicks to get a shot to fire. They can also tell you that the performance of these uncooperative mixes is often times on par with 'first light' mixes. Though a higher percentage are 'dud' shots, they can still be full power under certain circumstances, which means we are not getting the full picture.

Even if a bit more waiting will solve the problem, there is no definitive way to tell when the chamber has come to equilibrium and people will still fire their cannons when they are less than ready. Since we are talking about launchers with very high margins of error, the time the propane takes to completely diffuse is not consistent, can cannot be assigned a static value. (IE, wait 45 seconds before firing)

I have seen clear chamber launchers with stun gun ignitions spark for a while before the mix ignites, again, with powerful shots. The posted study is certainly interesting, but apparently (since it can be readily observed my most spudders) is a bit too far detached from the chamber aspect ratios and methods that most spudders use.

More information would be nice, but in the mean time, I have seen multi-spark systems work wonders, and can tell you that they do not prevent a cannon from firing, even if the first spark does not ignite the mixture.
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Unread postAuthor: TurboSuper » Wed Jun 04, 2008 5:45 pm

I can attest to that as well, mine works perfectly every time with a multiple sparking system. I've had some piezo's take a couple of clicks to get going, even with the fan (rare as it is).

You also have to understand that a piezo makes a loud "tic", even if the spark doesn't jump the gap. At least with a rapid electric one, you'll hear whether it's sparking or not.
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Unread postAuthor: Spuddin » Wed Jun 04, 2008 6:16 pm

TurboSuper wrote:I can attest to that as well, mine works perfectly every time with a multiple sparking system. I've had some piezo's take a couple of clicks to get going, even with the fan (rare as it is).

You also have to understand that a piezo makes a loud "tic", even if the spark doesn't jump the gap. At least with a rapid electric one, you'll hear whether it's sparking or not.

agreed 100%.
btw i was about to get bummed out because i currently have a piezo and it takes a couple "tics" but now i have a electric bbq that uses AA's and i cant wait to get it installed just because i want to.
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Unread postAuthor: jimmy101 » Thu Jun 05, 2008 2:09 pm

BC Pneumatics wrote:One cannot say a cannon will never ignite if continuous sparking is applied, just because one test proved that trying to ignite a fuel air mixture in a 27:1 chamber designed for slow diffusion once every several minutes does not work.

While these tests are certainly interesting and warrant further investigation, many spudders know that it sometimes takes a few clicks to get a shot to fire.

True enough, one set of data specifically designed to give a worst case scenario is hardly definitive. However, one set of data is all there is. The rest is anecdotal and complicated by the uncertainty in timing and whether or not there was actually a spark with the earlier clicks. Many spray-n-pray guns built by beginners have a spark gap that is too large. You don't get a spark everytime you push the clicker. Add in the possibility of gumming up the electrodes with whatever is in the aerosol (which may "un-gum" themselves if you wait a while so that low boilers in the aerosol can evaporate off the electrodes) and you really have no idea if 1 click = 1 spark. So, you can't say that the nth click that fired the gun was the first time there was a combustable mix at the gap or if some other affect of spray-n-pray, or the gap, or whatever, caused the affect.

I think there are significant problems with comparing mulit-click on a piezo with a circuit that sparks several times a second automatically. Different beasties operating in different time domains.
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Unread postAuthor: Canuck » Thu Jun 05, 2008 2:44 pm

I cant get my piezo to work properly in my new cannon, so im going to get an electronic ignition type. Yes you only need one spark to ignite a mixture, so hit the button thing once and dont hold it down... :D
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