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can't get my first thermojet to start?

Posted: Wed Oct 27, 2010 5:00 pm
by cactvs
First try with no math involved.
CC is 4.5" long and 3" in diameter. Intakes positioned on either side of the exhaust are 5/8" by 3.5" (flared).
Exhaust is 1" by 16.5". Propane injection from two 1/8" copper lines positioned in the flare of the intakes. Spark plug mounted opposite exhaust on other end of CC.
Won't start on spark, won't start with flame to one injector and air to the other, won't start with air and flame to one injector,
won't start with flame to the exhaust. I have a high pressure regulator so I have tried anywhere from zero to 60 psi.

Am I even close with the dimensions?

Just a newbie trying to learn by trial and error and FAILING so far.

Re: Please put your "I am new and need help" question here.

Posted: Wed Oct 27, 2010 7:45 pm
by metiz
It's a thermojet so you're always pretty close :lol:

I'd say decrease the intakes by 33mm. add a couple of mm to that to get a decent flare on your intakes
remove the restrictor from your propane tank
either make some rosscojectors or move your injectors further inside your intakes, say 30/50%
if you can't get the gas to light with your sparkplug, light a sparkler and toss it through the tailpipe into the cc, that'll get things started. don't be to agressive with the air, you'll only need a puff with a thermo like that

Re: Please put your "I am new and need help" question here.

Posted: Wed Oct 27, 2010 8:15 pm
by PyroJoe
I agree with metiz,

Intake looks a little long by about 0.71", also my stuff shows the tail is about 1.5" to short to start easily.

I would adjust the intakes first, an see how she does, if no joy, would weld a 3" extension on the tail and start shaving 0.25" slices off until she starts easy.

Echoing the above: remove the restrictor from your propane tank

Best of luck, an keep trying, its really nice when they fire up.

Joe

Re: Please put your "I am new and need help" question here.

Posted: Wed Oct 27, 2010 10:28 pm
by cactvs
Thanks guys.
I will try shortening the intakes and deepening the injectors first.
Hopefully I will get some pops to at least let me know I am making progress.

Thanks again...

Re: Please put your "I am new and need help" question here.

Posted: Wed Oct 27, 2010 10:43 pm
by metiz
you must also do away with the restrictor. this is rather important if you want your engine to run on a higher setting than stationairy. It will also help greatly with starting attempts.

Re: Please put your "I am new and need help" question here.

Posted: Thu Oct 28, 2010 1:16 am
by cactvs
No regulator? Even if it goes to 60 psi?
I guess I am unclear if need more volume of fuel or more velocity.

Re: Please put your "I am new and need help" question here.

Posted: Thu Oct 28, 2010 11:26 am
by metiz
Yep, even if it goes to 60. Tbh, you'll probably get it going with the regulator but it will not go a lot higher than stationairy, and that is asuming your engine has all the right proportions to run at low throttle. Just get rid of it to be sure. You can get some direct feed fittings for under 5$.

And to answer your question: you need more volume. and with volume comes speed if needed

Re: Please put your "I am new and need help" question here.

Posted: Thu Oct 28, 2010 9:55 pm
by nickwilson
Ok this is what i think. I dont know a quarter of what metiz or pyrojoe knows but with my expernce your injectors seem a bit large and when i first started thies things i used a shopvac and you have a small pj so that would work to not force feed it too much air and you did not say what type of injectors you are useing or what your gap is on the injectors that could be a big part of it not runing I have made some crazy thing run with trail and error

Re: Please put your "I am new and need help" question here.

Posted: Fri Oct 29, 2010 1:42 pm
by cactvs
Haven't had time to work on it yet.
Thanks again for your help, guys.
I will keep you posted.

Re: Please put your "I am new and need help" question here.

Posted: Mon Dec 06, 2010 2:43 am
by NeoFast
Hey guys, I am a newb and I hope I am putting this in the right place. I have been doing lots of reading on here as well as other places. I have been compiling a list of drawings, formulas, ideas etc. One thing that I have not seen, however, is a discussion on various fuel types. Any ideas on a good place to get information a various fuel types?

I have seen several using propane to run and or start. Also methanol, and even a comment about using straight diesel. I am interested in how valveless pulsejet engines react with different fuel types. I.E. run stability, ease of ignition, etc.
Any help would be a great. Thanks and have a great day.

Re: Please put your "I am new and need help" question here.

Posted: Wed Dec 22, 2010 12:37 am
by Zaitsev
How much Thicker does the steel that makes up the combustion chamber compared to the rest of it?

Re: Please put your "I am new and need help" question here.

Posted: Wed Dec 22, 2010 2:15 am
by Mike Everman
No need to make it thicker. You go thicker with carbon steel to get your engine to last longer before rusting out. On stainless, you can go quite thin, like .03" (.75mm) on motors that are less than 1m in length. You need more thickness to resist collapse on the low pressure part of the cycle.

Re: Please put your "I am new and need help" question here.

Posted: Thu Dec 23, 2010 12:15 pm
by alf
hi,

i am a total beginner, and i want to make a pulse jet engine, i dont particularly want the engine to be useful for propulsion purposes, or efficient for that matter, i just want it to work reasonably well lol, what engine is the best engine for a complete beginner to build?, should i use atomisation or direct injection?, and a few questions -

i want my engine to consist of a tail pipe, combustion chamber, air intake pipe, and a spark plug for starting, and a fuel pipe going into the intake pipe, like this one - http://www.cottrillcyclodyne.com/ElektraI/Elektra_I.gif,

i have a piezo electric sparker to use for starting ignition, and i can find a sparkplug lying about, thats not a problem, but my question is -

once the engine is started and running, is the propane gas supply constant?
can the propane canister be directly connected to the intake pipe, via a valve?
and will the engine suck in its own air once its running, and also -

do i have to build the engine correctly so that the fuel air mixture will be adjusted automatically when throttling,
or do i merely have to build the engine, find the correct fuel amount, and when its running, increase the fuel amount being supplied to increase its thrust?


thanks in advance, Alf.

Re: Please put your "I am new and need help" question here.

Posted: Thu Dec 23, 2010 1:48 pm
by metiz
alf wrote: i am a total beginner, and i want to make a pulse jet engine, i dont particularly want the engine to be useful for propulsion purposes, or efficient for that matter, i just want it to work reasonably well lol, what engine is the best engine for a complete beginner to build?
This one
alf wrote: once the engine is started and running, is the propane gas supply constant?
Yes.
alf wrote: can the propane canister be directly connected to the intake pipe, via a valve?
No.
alf wrote: and will the engine suck in its own air once its running
Yes.
alf wrote: do i have to build the engine correctly so that the fuel air mixture will be adjusted automatically when throttling,
or do i merely have to build the engine, find the correct fuel amount, and when its running, increase the fuel amount being supplied to increase its thrust?
Increasing or decreasing fuel wil throttle the engine up or down.

Re: Please put your "I am new and need help" question here.

Posted: Sat Jan 29, 2011 10:33 pm
by walker925
i'm only getting pops and bangs now. anything i can do to make it sustain?
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