Valveless pulsejet material

[owens65]

Has anyone considered using other materials to build a valveless pulsejet? I've read the biggest drawback for these engines is the noise level, I think this is due to the accustics of the metal being used.

[Viv]

I garantee it is not the metal that is making all the noise!

Its an explosion in a tube after all, it does not matter what the tube is made of the noise is going to come out of it.

We have had a number of threads on the old forum regarding materials even concret has been suggested.

Viv

[Psignorian]

Isn't it a deflagration rather than a detonation, which is what I think of when someone says explosion?

[Viv]

Isn't it a deflagration rather than a detonation, which is what I think of when someone says explosion?

Ok picky but true:-0 it is deflagration not detonation but we also have the front mode combustion half way house too:-)

Viv

[Mike Kirney]

We have had a number of threads on the old forum regarding materials even concret has been suggested.

Viv

Interestingly, nobody has suggested castable refractory, which is readily available for $35 a bag (55 lbs.) down in Ottawa. I'm eventually going to make a cupola furnace or an iron forge or both sometime this winter. The stuff I got is good to 2500 deg F, but the same company also makes Dukast 2800 and Dukast 3000. I would have got the 3000 deg stuff but I didn't know it existed and the guy just handed me this other stuff when I asked for 'fireclay'. Castable refractory is basically a mix of portland, alumina, silica, and vermiculite. The amount of alumina determines its maximum usable temperature. There is harldy any portland in it, just enough to bind everything together.

[Stuart]

Interestingly, nobody has suggested castable refractory, which is readily available for $35 a bag (55 lbs.) down in Ottawa. I'm eventually going to make a cupola furnace or an iron forge or both sometime this winter. The stuff I got is good to 2500 deg F, but the same company also makes Dukast 2800 and Dukast 3000. I would have got the 3000 deg stuff but I didn't know it existed and the guy just handed me this other stuff when I asked for 'fireclay'. Castable refractory is basically a mix of portland, alumina, silica, and vermiculite. The amount of alumina determines its maximum usable temperature. There is harldy any portland in it, just enough to bind everything together

Do you have to fire this stuff? Sounds like no.
Is it someting you could slip mold somehow, I wonder? Sounds like great stuff, especially for cones.

[Mike Kirney]

[quote="Stuart
Do you have to fire this stuff? Sounds like no.
Is it someting you could slip mold somehow, I wonder? Sounds like great stuff, especially for cones.[/quote]

The data sheet from the manufacturer claims that you should use only 3 litres of water per bag. Each bag contains about 11.5 litres of dry matter, so it sounds like a pretty stiff mix to me, but you could add more water if you wanted. You would get a less viscous mix but the dry strength of your item would be greatly reduced. Apparently, the material is workable like wood once it has set. As for firing etc., it is recommended that you air-dry your casting for at least 24 hrs, then bake it for a couple of hours at 400 or 500 deg F, then, in the case of a cupola or forge, pack it with coke/charcoal as if you were going to do some melting, and gradually bring the temp up to operating max over several hours. You want to drive out the excess water gradually so that it does not boil all at once and blow the thing apart. With a pulsejet I think I would air dry it indoors fro a night or two, then bake it in my kitchen stove for four or five hours, then fire it up with minimum fuel flow for the first few runs, then I would crank it up full blast. Obviously, the sectional thickness of your cast item would dictate how much pre-heating you would need to boil off the excess moisture. Cupolas and forges usually have refractory layers of over 2" thick, so they take hours to dry out, but perhaps you could make a valveless jet duct that is only 1/2" thick or so.

[Mark]

Has anyone considered using other materials to build a valveless pulsejet? I've read the biggest drawback for these engines is the noise level, I think this is due to the accustics of the metal being used.

As with experimental automobile engines made of ceramic which have less vibrational energy to deal with than a vibrating pulsejet, it's a tough pickle to make something ceramic that doesn't vibrate itself apart. What is needed is some rip-stop ceramic, like the rip-stop nylon, nylon's name coming from chemists in New York and London, (NY-LON) you know how glass likes to cleave like a diamond with just the merest scarification. Or like those tough plastics you can tug and strain and they don't tear, but cut them with a scissors to start it and it goes like soft butter. Crumbling is what holds this back. Why even metals must fight hard to hold together. Poor Hanna flew to find rivets vibrating out, was it?
Mark
Mark