can't ignite

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walker925
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can't ignite

Post by walker925 » Sat Jan 29, 2011 5:48 pm

i've got everything i thought i needed: propane, sparkplug, air gun, etc. but it won't ignite. I'm using a magneto from a weed eater to spark the plug and i've got a copper line running through the intake to the combustion chamber for the propane. is there anything i'm forgetting to do?

keith mcconnell
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Re: can't ignite

Post by keith mcconnell » Sat Jan 29, 2011 6:16 pm

What's it doing? Get some good video that will help.
keith

walker925
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Re: can't ignite

Post by walker925 » Sat Jan 29, 2011 6:51 pm

it's not doing anything really. i'm trying to upload a video now, but my internet is slow. my spark plug won't ignite the propane
100MEDIA_IMAG0038.jpg

metiz
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Re: can't ignite

Post by metiz » Sat Jan 29, 2011 7:37 pm

open up the sparkgap
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walker925
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Re: can't ignite

Post by walker925 » Sat Jan 29, 2011 8:34 pm

i filed down the nut thats holding the sparkplug in place and opened up the gap, but it is still not working

walker925
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Re: can't ignite

Post by walker925 » Sat Jan 29, 2011 10:26 pm

alright now i've got it to ignite, but all it is doing poping and banging. how do i get it to sustain?

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Re: can't ignite

Post by HPSCL » Sun Jan 30, 2011 5:07 pm

  • °- The length of your tailpipe should be 11 times the I.D. (Inside Diameter).
    °- The INSIDE of the end of the tailpipe should be filed, so that there is a smooth taper.
    °- Calculate the volume of the finished tailpipe. ( Pi x R² x length)
    °- Your combustion chamber's volume should EQUAL the tailpipe's volume.
    °- The intake should be 1/6 of the length of the engine ( length of combustion chamber + length of tailpipe = "X" ... "X" divided by 6 = intake length.
    °- The INSIDE of the end of the intake should be filed, so that there is a smooth taper.
    °- Your spark plug's electrodes should not be shrouded. ( They must protrude into the combustion chamber )
    °- A spark plug is really not necessary, as you can simply light the end of the tailpipe.
    °- The end of fuel line needs to be pinched so small (for an engine of this size) that there is just barely enough gap to blow air through... A lot of trial-and-error.
    °- The end of the fuel line will need to be placed about 1/4" to 1/2" inside the opening of the intake and centered.
    °- The "pinch" in your intake (just before combustion chamber) will disrupt airflow and make it harder to sustain.
    °- A regulator will be required for the gas. ( IT will REALLY helps to sustain a CONSTANT pressure, which will help [ a LOT] to get it running.

walker925
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Re: can't ignite

Post by walker925 » Sun Jan 30, 2011 9:39 pm

how do i start it with an open flame at the tailpipe? i made the changes to it that you suggested.
100MEDIA_IMAG0043.jpg
we're not getting kind of pulsation. just fire. i don't have a regulator for it, and i'm not getting any poping like i was before

HPSCL
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Re: can't ignite

Post by HPSCL » Mon Jan 31, 2011 1:40 am

It (more than likely) won't, with the way you have it set-up now. The reason being, is that you have it configured "Shubert"-style. (With the intake and tailpipe "inline". The engine's flame-front will cycle straight back-and-forth, rather than circulate. I've found that kind of configuration extremely difficult to sustain combustion.

The flame would be better cycling back-and-forth. (With the entrance to the intake and the exit of the tailpipe facing in the same direction). I am truly sorry that I failed to mention that your intake pipe's I.D. should be HALF of the tailpipe's I.D. - - - But your first image (before you modified the engine) appeared to have a smaller intake, than the exhaust?

Try these mods (shown in the included picture)

To light, simply use a BBQ Lighter to light the opening at the end of the tailpipe.

EDIT: Please note, that there's no guarantee, that this'll work. It's simply a suggestion.
Attachments
pipe pj.JPG
MODS

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Re: can't ignite

Post by Mike Everman » Mon Jan 31, 2011 3:31 am

so, is that 1.5" nipples on the CC? I doubt very much this can work. A 2" CC is hard enough, and I've made several. Bent or straight doesn't matter much.
Random notes:
Sealing on small PJ's is critical. You really need to gronk on these fittings to have a chance.
1.5 is too small, sorry.
But if you are going to continue, that fuel line needs to go down to 1/8 od if you can find it.

The main reason Mark's Logan runs is that he's using methanol which has a higher flame speed and allows a smaller cc dimension. The only valveless I've seen work on propane at 1.5" dia is a thermojet style.

the small size makes for greif on a first effort. I fear it will kill your enthusiasm.
Mike Often wrong, never unsure.
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walker925
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Re: can't ignite

Post by walker925 » Mon Jan 31, 2011 3:44 am

yeah it did have a smaller intake. I got rid of it because of it's poor bending and tried the Shubert way, but my dad bought the wrong size pipe. We tried it anyway though. thanks for the help though, I'm going to buy those new parts tomorrow and see if it works then

HPSCL
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Re: can't ignite

Post by HPSCL » Mon Jan 31, 2011 5:01 am

As Mr. Everman stated; If you're not able to achieve a leak-free joint, it'll make the engine much more difficult to get running. Even if by some chance you do get it running, a small leak will severely limit it's throttle range. - Another downside is the fact that you're using galvanized pipe. I've been told that the fumes (from the hot pipe) are toxic.

If there is any way at all that you and your Dad can possibly weld some pipe together, then the availability of exhaust tubing will make any valveless pulse-jet project, pretty easy to build.

I've built several, if you care to check some of them out: El-Cheapo pj's

walker925
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Re: can't ignite

Post by walker925 » Mon Jan 31, 2011 6:57 pm

i don't plan on running the pipe over like 5 minutes, but i do have access to welding materials. do i need a bigger combustion chamber? i could weld the two couplings together and get rid of the nipple in the middle, but if that's not big enough then i could just try to make a bigger one. I'll just have to recalculate the lengths and volumes of the intake and tailpipe. and also my tailpipe is 3/4 inch diameter; will a 1/2 inch intake be good enough? or does it need to be smaller?

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Re: can't ignite

Post by Mike Everman » Mon Jan 31, 2011 7:10 pm

No problem if you want to make a pipe fitting jet. Just follow the "pipewood" plans. That one's been run successfully by several people. It is a 2" chamber.
Mike Often wrong, never unsure.
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walker925
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Re: can't ignite

Post by walker925 » Mon Jan 31, 2011 7:18 pm

where do i find that?

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