problems starting a lpg/propane pj

[drhammer]

Hey guys, Im sure im repeating a question thats already been asked a million times but Im at a loss.
I just built my first pj. Its set up to run on propane from those small 16oz campstove tanks and I used the engine calculator on this site to design it for 10 lbs of thrust. I work 8-5 as a fabricator so I made it all from scratch from the fuel valve to the tail pipe and it came out looking pretty good.
Only problem is I cant get it to start...admittedly I dont have it set up with a sparkplug, Im using a torch and trying to light it from the end but the best Ive been able to get was the occational bang. Most of the time it just has a flame coming out the end of the tail and when I hit it with the air blower it makes a bigger flame, turns to a blue flame and then makes a humming sound before going out. Is there too much propane, too little air from the air blower or am I just missing something completely?

[tufty]

I assume you have removed any regulator and flow restrictions. I'd try with a big tank first. If nothing else, by the time you've got the hang of starting it, if you have a small tank (and 16oz is very small), you'll be out of gas.

And remember, no regulator.

[metiz]

a 16 oz bottle won't do, an air blower won't do. Use an unregulated camping propane bottle and a leafblower/ shopvac/ or aircompressor

[drhammer]

Camping propane bottles are 16 oz (16.4 by the label). Not using a regulator, I had read about the issues with them and opted to make a ball valve that screws directly onto the bottle and the other end attaches directly to front of the valve head via the 3/8 fine thread on the fuel injector. This ball valve will be operated by a servo on the flying platform to control the power and provide an emergency shutoff...that is if I ever get this thing running
Going to borrow a leaf blower and try that.
Will post some pictures when I get off work

[metiz]

I'm not familiar with the "oz" scale. every time I punch in 16 oz propane bottle I see the small bottles. If you have a big one, no worries then. You'll need one of these:

[Bruce Simpson]

Firstly, be aware that unless it specifically states otherwise, there's a fair chance that the camping gas will contain high levels of butane which sucks as a pulsejet fuel. It's boiling temperature is too high so it produces very little vapor pressure. You really need good propane.

Secondly, you're going to need a decent sized cylinder, especially if you intend to run on propane gas rather than liquid propane.

Do a google for "latent heat of vaporization" to see what's going to happen as soon as you start drawing any significant amount of gas from a propane cylinder and why (as a result) the pressure will soon drop, which in turn will produce a reduced flow.

I find that a 9Kg BBQ cylinder is the most cost-effective fuel source.

[drhammer]

Thank you guys for all of the advice thus far. I hooked it up to a regular grill sized tank tonight and used an electric leaf blower. I can get it to make a vibrating noise similar to all the videos Ive seen of a pj working but without the blower right by the valve head it stops. I know I have some good fire going because I can see it past the edge of the valves when they are vibrating (bright blue flame) but once again it wont work without the leafblower directly on it. I think it could be one of two things...
1. I bent the valves slightly back towards the valve head so they would seal tightly against it with the retainer in place. Maybe this wasnt a good idea or maybe I did it too much so that the low pressure phase cant pull them open to breathe and its not getting any O2 without the blower assisting.
2. Its not able to pull enough air through the valvehead (ie. the holes arnt big enough)
I will post some pictures so you guys can see. Once again thank you all for taking the time to help a newbie
PS. the tank in this picture was the one I was going to use originally. Ive since moved up to a regular sized (20# ?) tank

[drhammer]

This is the tail pipe. disregard the clutter on the table, various shop projects and such

[drhammer]

This is the valvehead fresh out of the machining center

[drhammer]

Here we have the valve head installed with the fuel injector in place as well as the 0.006" blue tempered spring steel petal valve. The injector has a 1/4" hole for the fuel and screws into the valvehead with 3/8"-24 threads

[drhammer]

this is a poor quality pic of the ball valve that attaches the tank to the injector. Its powdercoated "wet black" which makes it look weird in the picture. I set this to the side to hook up the larger tank with an adapter I made up after work. The valve retainer and fuel injector set up is done the same way as shown on Bruce Simpson's site here: http://www.aardvark.co.nz/pjet/newvalving.shtml
P.S. Bruce, I spent hours scouring your site for info and ideas before making this pj. Its awesome to hear from people as knowlegable as you and the others here!

[drhammer]

well at this point im getting pretty discouraged. Ive moved up to a bigger tank, tried for two days with a leaf blower, and beat my head on the wall for hours hoping something useful would come out but im stuck. Remeasured the tailpipe and all the measurments check out. Not using a regulator. Tried less fuel to the point that there is next to nothing coming out, tried more fuel till the fireball coming out of the end was bigger than I was and the leaf blower was pointless. Just about to the point of throwing it away and heading to the bar. What do I do? Are these things always this much of a headache?

[Bruce Simpson]

Can you take some video and post it to YouTube so we can see what it's doing?

[drhammer]

got a video on my phone, will upload it after work. tried flattening the petal valve last night and it was easier to get it going (at least I think it was going) but it still isnt self sustaining and quits when I take the leaf blower away. It also isnt as loud as I was expecting, in the video you can barely hear it over the leaf blower

[drhammer]

http://www.youtube.com/watch?v=_Qvm5KQM ... tube_gdata