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Ignition Problems

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Ignition Problems

Unread postAuthor: noname » Fri Jul 27, 2007 8:31 pm

I've redone my steel hybrid, to get the spark in a better place, and so it's more compact and easier to use. I made a new propane meter, and now it won't shoot.
Chamber volume is 787 mL.
Meter Volume is 38 mL.
According to Latke's FuelTool, I need 4.83 psi in the meter for a 4.2% mixture. According to SpudTool, I need 5.05 psi for a 4.2% volume. I've tried both without success in a 1x mix, so concluded that the fuel wasn't mixed well enough. I tried 2x mixes. I injected propane twice, then pumped the gun to 10 psi and got out my shock pump. 1 pump with the shock pump = .3 psi in the gun. I pumped once, clicked the igniter, pumped again, clicked the igniter, etc. I did this until the cannon was at 25 psi.
Any ideas?
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Unread postAuthor: iPaintball » Fri Jul 27, 2007 8:44 pm

Wouldn't it just be easier to use just a single nipple as a meter pipe instead of that whole thing?
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Unread postAuthor: SpudBlaster15 » Fri Jul 27, 2007 8:44 pm

Based on the pictures, my 2 second analysis would be that your meter design inhibits the mixing action of the air and fuel as your pressurize the gun with the pump. Try redesigning it such that the air inlet is situated directly at the back of the meter pipe, right next to the propane regulator.

EDIT: My 30 second gas law calculations show that you should actually be using 13psi.

EDIT2: Looks like you already figured that out.
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Last edited by SpudBlaster15 on Fri Jul 27, 2007 8:52 pm, edited 2 times in total.
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Unread postAuthor: noname » Fri Jul 27, 2007 8:46 pm

Over here or something?


EDIT: I plugged the numbers back into both calculators and now they agree on 13 psi. :? I guess I'll go try it.
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Unread postAuthor: iPaintball » Fri Jul 27, 2007 8:54 pm

Maybe I'm just an idiot, but it looks to me like all the fittings up to the bigger ball valve are being used as the meter.
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Unread postAuthor: SpudBlaster15 » Fri Jul 27, 2007 8:56 pm

noname wrote:Over here or something?


More like here.

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Unread postAuthor: Fnord » Fri Jul 27, 2007 9:07 pm

Ya know, it's a lot easier if you have a meter pipe that is as close as possible to 4.2% of the chamber volume. The meter on my hybrid is nearly perfect, so all I have to do is use an extra 15 psi for every mix.

Also, you did make sure it's actually the meter and not the new spark gap, right? Maybe you have a short somewhere.

If you are sure it is the meter, try running the mix too rich on purpose. 4.2% is very near the minimum explosive limit for propane(3%), so your mix might be too lean. I think the maximum explosive limit is something like 9%, so try and start there, and work your way down.
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Unread postAuthor: noname » Fri Jul 27, 2007 11:49 pm

iPaintball, yes, they are.
SpudBlaster, I'll try it.

[quote=_Fnord"]all I have to do is use an extra 15 psi for every mix.[/quote]

This is propane you're talking about, yes?
The spark plug works great, I get a 1/16" spark every time. I can check for the spark by holding the wire 1/4" away from the chamber, and the spark jumps there too, even under 30 psi chamber pressure.
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Unread postAuthor: Fnord » Sat Jul 28, 2007 10:20 am

This is propane you're talking about, yes?


Yes, it is.
An extra 15 psi in the meter is what I meant.
As an example, for 2x I would put 30 psi in the meter, 45 psi for 3x, etc.

Sorry if my original post was hard to understand; I was tired.
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Unread postAuthor: dongfang » Sun Jul 29, 2007 7:43 am

Hi,

Can somebody explain to me what this all is; I have never build a pressurized gas meter before (but I have built a pressureless)....

The knob on the right, is that a gas pressure regulator? Does the knob control pressure on the output side?
Is the gauge in the right on the input or output side of the regulator?

What is the gadget with the wheel thing on the left? And that long black pipe?

And finally, in my logic (of lack of it), if I were to build it I'd put a tee in one end of the meter pipe, and put air injection on one side (as close as possible) and gas on the other. In the other end og the meter pipe, the cannon through a ball valve. Anything wrong with that design?

Regards
Soren
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Unread postAuthor: spanerman » Fri Aug 03, 2007 8:49 am

dogfang, correct me iff im wrong but are you describing a design similar to this?Image

iff so, yes it will work, im in the processs of building mine, but spudblaster15 has made one(he was the pioneer of this design) and it functions!
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Unread postAuthor: noname » Fri Aug 03, 2007 11:03 am

Spanerman, read the topic or don't post in it. Simple, no?
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Unread postAuthor: spanerman » Fri Aug 03, 2007 11:24 am

i read it ALL, im trying to help the use above me who posted a question...got a problem with that? please pm me with your isssue
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Unread postAuthor: noname » Fri Aug 03, 2007 11:36 am

Did you manage to miss the pictures of my setup (which dongfang is describing) while reading the whole topic? Seems like it.
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Unread postAuthor: spanerman » Fri Aug 03, 2007 11:46 am

no, i saw them but they seem unclear to me, i had to look at them for a while to see what each component was.....regulator...sock pump ect. so i thaught that i would post a simple diagram to be of some help, sorry if you feel ive done something wrong please notify me and il editmy post or request that its removed.
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