Hagen's Big PJ

[hagent]

Hey Thanks Eric for the info.

I was wondering what happend to you. Glad to here you have so many projects to keep you busy, if you get $1 for half of those projects you can adopt me:)

I don't have any round stock on hand... So I'll have to get some or think up a different solution.

Thanks for the injector idea. So I seem to remember that one of your injectors produced a liquid umbrella of propane, and this liquid would help cool the intake air mass. So is it better to have it liquid or vapor?

I guess a hot vapor would be best since mixing would be faster.

I have to admit that my injector is pretty lame.

And I'll be trying a different one next time.

I'll post a few ideas and you could tell me which one would be best.

Thanks,

[Eric]

With this big of an engine on full throttle there will be an enormous cooling effect from that much liquid propane.

Propane expands 280 times in volume from liquid to gas, so it has a massive potential for cooling.

With an injector internal expansion ratio of 20, even if you super heat the fuel in the injector, once it expands the rest of the way the temperature is going to be pretty cool, not as freezing cold as injecting liquid directly though.

The bit of preheating and expansion in the injector gives it the perfect combination of cooling, while keeping the vapor temps high enough to mix and burn extremely well.

Here is a sketch of the "bullet" part of the injector that you can make. Basically you just need some round stock, probably 1.25" and some 1/2" round stock to make the central shaft, as well as some 1.25" OD tube.

Once you make the bullet section you can weld the large part of the fuel tube to the back of the tube part of the bullet.

So you would have 1/4" OD tube leading to 5/8" OD tube, Leading to a 1.25" OD injector.

That should give you an expansion ratio of 35 or so.

What would you say the throttle level was in the you tube video? I'm interested to figure out how your current max throttle relates to the engines max potential. I suspect that it could be below 50% even.

When you get near full throttle you will know it, you will have the uncontrollable urge to run away and curl up into a fetal position to minimize sound absorption, and the ground will litterally be shaking. If you have ear plugs and ear muffs, and jump, the sound will be greatly reduced because you will not be absorbing it from the vibrating ground.

The 180's running at max throttle are truely a scary experience.

I have all of those sizes of tubing and round stock available, I could cut off a few inches/ feet of whatever you need if you cant get any there.

Eric

[hagent]

Hey Eric,

Thanks for all the good info.

Based upon your discription of earth shattering force, I do have to admit that my pulse jet was not at that level. So with that said I probably was flaming out because of bad fuel setup. It did seem to be putting out a good amount of thrust but I didn't have a scale on it so I really don't know.

I do have one important question though. I set this up so the fuel can be fed into the intake from the side. As you know I can remove the intake and change the fuel injector if needed. I can also change the length of the intake by a few inches at will. Is it better to insert the injector from the CC or the intake? If I do the CC then it becomes more of a permenant feature and much more dificult to swap out and try new things.

Thanks very much for posting the drawing.

[hagent]

Ok here is a drawing of an injector that I was thinking of.

The small fuel tube enters the intake and make a 90 deg turn.

It then enters a larger tube, at the end of the large tube the small tube has holes in it to let the propane out. The propane expands and flows into the large tube and towards the other end where it exits out of a number of small round holes in a circle. The propane then hits a semi circle disk and get evenly dispersed back into the CC.

The propane should pickup a lot of heat energy.

What do you think?

I'm just trying to get around putting anything directly into the CC.

[Eric]

You could set up the injector I drew so it could be in the intake. I dont like putting them in the intake because it obviously blocks more flow, but with a big engine like yours it wouldnt be much of a problem.

you could even put the tubing in a vice to make it an eliptical shape for less drag.

The problem with holes, and why I havent used any injectors with radial hole patterns in a very long time, is that even with a lot of holes, you cant get as good of mixing as with the infinijector style anular fuel gap. The anular gap gives you more fuel spray surface area, more air sucked up into the fuel, more turbulent mixing, faster mix time, faster burn rate, and tons more power.

Having a lot of the injector stick into the engine to gather heat only works to a point, unless you put more of a restriction in the system than the 1/4" tube so you get an even larger expansion ratio, but then you lose the ability to start on an upright tank. A few inches will probably get you plenty of heat. Without a higher expansion ratio, the propane is just going to heat up to whatever the max temp is and not pick up any more heat from the injector.

Eric

[hagent]

Thanks Eric,

I think I might just have to take you up on your offer to send me some short pieces of tubing.

Let me know how much I owe you for shipping, materials, and your troubles.

Oh and if you have some of that 1/8" 304 round stock for me to put on the exhaust that would be of great help. I don't mind paying.

I don't get a chance to go too often to the metal supply store.

And again thanks for your help.

Hagen

[hagent]

Here are some photos of the extra bracing that I did to the frame that holds the PJ. It doesn't look like much but it seems to be working well.

As Eric pointed out there is a harmonic flexing at the very end of the exhaust that I will have to dampen out with some added support.

I didn't have any rolling type tools, so my cones are not perfect, they were all done with brute force.

[adam]

hey eric, the engine you built me cracked where the injector is welded on the cone section, i was thinking this is because there is a lot of heat there but right now i am currently building another exact replica of the one i have now except every thing is going to be made with stainless steel tubing that is all 18 guage thickness instead of using rolled sheet metal, good idea or bad idea since i beleive that even a perfectly round pipe has a weld or seem that runs down the length of it instead of a big jagged weld, you think heat can affect the seem or weld on a pipe worse than a thicker weld on rolled sheet metal?, im just going for a more prettier look i guess with the pipe stock i have. well back to the subject, like in hagents drawing, would it be allright to mount or weld the injector or tube that connects to the injector right threw the intake pipe so that way it wont be prone to crack easy because there isnt as much heat there as the cone section on the combustion chamber or would this interfer more with the air flow resistance since the intake tube is a smaller area and is being blocked by some tubing that runs threw it possibally causing turbulence? please help!! here is a sketch.

[Eric]

18 gauge stainless tube should work well.

You can put the injector in the intake like that, it shouldnt be too much of a problem.

I've been thinking about the crack at the base of the injector. That area should be cooled quite a bit by the propane, where the sorrounding sheet metal would be red hot. I think also over all the time that you ran the engine, the injector may have been vibrating back and forth a tiny distance, which has lead up to some work hardening stress along the weld which would remain cooler.

If the injection tube were doubled, so there would be an identical tube on the other side, connected in the middle at the injector, that would keep the air flow from flexing it back and forth.

If you have the injector in the intake, the temperatures will be much lower, but also the local air velocity will be much greater, so there will be more drag and more flexing, so It may not last any longer.