Valveless Pulsejet Engine

[Axt]

Been thinking about them for the last couple days, trying to think up one that is easily manufactured. Below is what I may try -

<img src="http://ww1.altlist.com/~52497/rogue.altlist.com/images/jetengine.jpg">

Is the hot intake going to be a big hinderance? thats the only possible flaw I can see. Even if its not a terribly efficient design do you think it would run at all?

If anyone has any experiance at all I would like to hear it.

Heres a mpeg of a valveless pulsejet in action - <a href="http://www.brainvirus.org/jetrun2.mpg">MPEG</a>

Another - <a href="http://www.aardvark.co.nz/pjet/images/kartrun2.mpg">foot on brake mpeg</a>

[Tuatara]

Funny thing is, the moment i saw the title of this thread i thought of all the U shaped designs I've seen on the web, and wondered if some sort of concentric design would work. And Lo! theres your picky of a concentric design.

There are two possible issues I can see:
1. In any heat engine you want the coldest intake air you can, because of the Carnot efficiency limit and the greater air density.
2. that section of the exhaust tube which sits inside the inlet tube is going to get bloody hot.

However The hotter inlet air may allow you to use a less volatile fuel, eg Kerosene. You could also use your fuel to cool the exhaust tube by either wrapping a metal fuel line around it or using a double wall tube. The spark would then be placed where the fuel entry is on you diagram and the fuel would be injected back towards the spark from the inner end of the exhaust tube.
You might also be able to add a third tube out side the inlet tube to act as a venturi driven by the short pulse that comes out the inlet, in order to draw cool air from the front of the engine (pure speculation here).

Hope you've got good ear protection! I understand these things are insanely loud. Would that make it qualify as an improvised weapon?

[Axt]

Noise is the main reason I want one .. I like loud noise (when im making it). .. heh heh. That second movie is a New Zealander, you may have heard him. (check out his <a href="http://www.aardvark.co.nz/pjet/">site</a>, making a cruise missile)

I would use propane, as valveless engines need to be fuel-injected, and there no room for fuel feeding problems. Gaseous fuel seems like a far easier way of doing it.

It may not get that (relatively) hot, considering how the intake from the U designs never goes red like the rest, the constant air flow keeps it cool. The ribs aligning the exhaust will also aid in cooling (perhaps).

Tests will have to be done!

[kingspaz]

the problem i see is, how the hell is it going to suck air into it if the air intake is facing the opposite direction of travel. the intake MUST be on the front since the engine cannot draw air into itself. being on the front allows air to flow in as the thing moves. also in your design there is no reason why it can't exhaust out of the intake.

[Axt]

Ummm...

Did you download the movies? The air <b>IS</b> sucked in the back and the combustion gassed <b>DO</b> come out the air intake, hence the reason intake is at back - to add thrust.

[Tuatara]

Kingspaz, what you describe is essentially a ramjet. The pulse jet only works because the moving mass of gas heading out the exhaust can create a negative pressure behind it. This would normally open a reed valve to draw more air in. The valveless pulse jet relies on the mass in the inlet being less than in the exhaust. The are also resonant factors at work. And air, being a fluid, will happily go around corners :p

Actually Axt, you might want to make the length of the inlet tube adjustable, with a close fitting outer sleeve. I would not be surprised if there is an optimum length ratio between inlet and exhaust. Make one tunable and you wont need long hours in front of a calculator

[Axt]

Ive actually been thinking about that Tuatara, while the design is simple to make (ive since found out it HAS been done before), its near impossible to modify if not made exact the first time. Theres most definately an optimum length, and seemingly quite a narrow one from what ive read.

Ive redisigned it to be easy to modify and take down. Hopefully if made with the exhaust/intake longer you could just chop them back until it resonates, no point getting fancy when the likelyhood of it working is slim.

<img src="http://ww1.altlist.com/~52497/rogue.altlist.com/images/streamjet.jpg">

Its also just joined via a flange so easy access to the fuel line.

[Axt]

Intercooled concept -

<img src="http://ww1.altlist.com/~52497/rogue.altlist.com/images/intercooled.jpg">

I think you meant to say wrap the fuel line around the intake rather then the exhaust tuatara. Sounds like a good idea thats easy to test.

The thing im finding hardest to design is delaying the ignition, as the red hot steel will ignite the gas as soon as it hits air, out of sync with the pulse - fuel injector placement will take some thought (im guessing).

[Mr Cool]

I would love to make a pulse-jet engine. I don't have the tools though :(. My CDT teacher at school made a jet engine, a foot or so long, and that was cool. It made a deafening, whining roar and shot out blue flames :D.
There seem to be plenty of plans on the 'net for all kinds of engines, so one shouldn't be too hard if you have a spot welder and perhaps a lather and milling machine.
Fuck, I just watched those vids - look at 'em glow!! They look fucking sweet.
Axt, another great project if you like noise would be a copper halide vapour laser with a mechanical spark gap. You get a spinning wheel with deafening sparks shooting off its circumference at many hundred Hz, and intense golden green beams of light (several dozen watts in a big one, easily enough to burn holes through stuff) shinning out of a red-hot block of refractory - they're the stuff that Sci-fi horror movies are made of :D. Would be easy to make with a lathe and milling machine, if you're into that kind of stuff. I did have a vid, if I can find it I'll post it just because it looks cool.

Anyway, back to jets... I don't think I've seen this design before. I saw some that had slits at the front wich let the air in, and behind the slits were strips of metal, arranged radially around a central shaft. At the other end of the shaft was an impeller, with the combustion chamber between the two ends. The impeller spun due to exhaust gases passing over it, and this sequentially covered and uncovered the slits at the front. The thing was timed so that the fuel was ignited while the slits were closed, pushing exhaust out the back. When they were opened, the negative pressure sucked more air in and mixed it with fuel. The momentum of the impeller/shaft carried it round, closing the slits again and the cycle repeated. For this you would need to be a good metal worker, but this design looks much simpler - the kind of thing you might be able to knock together out of plumbing and tin cans, if you only wanted a small one (inefficient, but loud :)).

Edit: haha, that's made me a happy man. My computer crashed half-way through replying, and I thought my reply was lost. OK, so it isn't very useful, but it's still anoying when you type them up and they get deleted.

[kingspaz]

Tuatara, thanks for correcting me. i ALWAYS get those mixed up :(

[Axt]

What! ... a "copper halide vapour laser with a mechanical spark gap" .... now that would just make me a nerd! heh heh.. would like the vid if you can find it. Funnily while I like making loud noise, im the only one I know that cant stand any forms of music, its sends me insane!

I havnt seen a design like you posted, but its simular to most pulse jets which use valves, the valves on a V1 operating are easily seen on this <a href="http://www.aardvark.co.nz/pjet/images/v101.mpg">movie</a>. supposedly the valves need replacing every run, that really sucks since the valves are the only hard bit to make! valveless are less fuel efficient but dont need any maintenance.

I run the idea in the last pic I posted by some pulsejet gurus and they gave it the thumbs up, somewhat inspiring.

[Mr Cool]

Lol, yes it would make you a nerd. But you would be a loud nerd.

[mt1988]

he also making plan for a no weld pulse jet
http://www.aardvark.co.nz/pjet/noweld.shtml
for a donation you can see the draft copy of his book which has every thing you would want on pulsejets, once ive finished my Boosted dart project going 30,000 Feet, im build a ramjet with a soild booster

matt

[Axt]

The jet powered trike!

http://ww1.altlist.com/~52497/rogue.altlist.com/images/jet-strike.jpg

The lockwood (patent #3462955) power source was chosen because its something tried and true, no point trying something fancy so it doesnt work, getting all dismal about it and having the shits for a month.

Bike tyre / 1.5" tube construction, easy enough (i hope). Everything else i'll work out when I get to it.

Seems like im going to need massive twin 12" wide combustion chambers on the thing to get it moving spritely enough. With an estimated fuel consumption of 4 litres a minute.... damn!

[Axt]

Yes, im an electronics retard, so could someone answer the questions presented in the circuit diagram below. Is this circuit the best way of getting a repeating spark, or is there a better way of doing it?

http://ww1.altlist.com/~52497/rogue.altlist.com/images/circuit.jpg

Ive drawn up the likely configuration of the kart below, Ive inverted the wheels so that there is two at the front as its more stable and lets me use the back end of a motorbike - therefor readymade brakes and suspension.

http://ww1.altlist.com/~52497/rogue.altlist.com/images/framefulltwintank.jpg

[McGuyver]

I'd make it 4 wheels if I were you man. With only 1 wheel in the back it will still be pretty unstable. I would put two in the back and make the axles as long as you can. If this thing gets up to a decent speed you don't want it to roll for a mile if you have to turn sharp at a high speed. Maybe if your front tire has a very small turning radius but even so. You can buy like a go-cart axle and have really good hydraulic brakes and nice wide tires for more stability.

1. Those ends are where you need to connect your battery. Positive (+) 12 volts DC gets connected to the top, and negative (-) or ground gets connected to the other side.

2. The 1N4004 is a diode. On the diode there will be a line around the diode that is closer to one side than the other, put it the way it shows on the schematic.

3. For the capacitor, sometimes it doesn't matter what side gets connected where, I believe it has to do with the cap is made of, or it could be the low capacitance, not sure.

I have another circuit somewhere that makes plenty of spark and works on about 3V - two C or D type batteries. The only thing is you have to do is get a E type transformer form and wind your own transformer. Winding the transformer is kind of a pain. The rest of the parts you can buy or find, I'll scan it if you think you want it. I used the circuit to make a stun gun.

[Tuatara]

Well, maybe not the best way to get a spark, but it will work. Using an automotive ignition coil takes care of the hard part.

There are a few nasties in this circuit.
1/ there is no control of the peak current in the coil - it is limited only by the ignition coil resistance
2/ T2 will get bloody hot, so bolt it to a BIG piece of aluminium heatsink

On q3 the cap will likely be either polyester or ceramic type, so polarity doesn't matter. Only electrolytic (eg the 220uF one in your circuit) and tantalum caps are polarised


Love the pics! Are you sure you want your propane tanks that close to the engines?

[Axt]

Thanks guys..

Mcguyver, i would think that 3v circuit you describe takes too long to rercharge to give a repeating spark that I need, wouldnt it. And I think a 12v battery will end up being used to provide some starting air for the engines so 12v = good.

I dont think there will be great stability issues, it is a straight line machine. The inverted trikes are supposed to be nearly as stable as the 4 wheelers and have less ground friction. Theres a lot of homebuilt 3-wheelers here (http://www.ccpc.net/~jaho/3wheel2.html) and none look like slow machines!

Ive actually already stripped down an old AG100 to use the rear end, 1 fuel tank, a seat and an engine is nearly completed so its well underway.

As for the closeness of the tanks to the engine, the tanks are likely to last about 5min of run time. At that rate im hoping the tanks will get cold enough that the engine heat will have no effect on them and if they do it could well be a positive effect, keeping them warm so that they keep delivering pressure.

[priapo]

You have made a good choice with the dual wheel in front but if you have chosen this configuration trying to get less friction you have mistaken something.

Front wheels needn't be so thick as you are not going to get high speeds. I would use at least 19'' bike wheels. These, apart from having less resistance with the road have a bigger diameter than the ones you chose what leads in getting less vibrations in the vehicle (specially in the junction between the wheel and the chasis).

I would also place the wheels in having a small angle from their natural position (they would look this way /--\), doing this you will take better the curves, giving more stability to the vehicle too.

I am quite close to car projects that compete in the Shell Eco Marathon race and this is the configuration we use. I also have the project in IDEAs format if you want to take a look at it.

Again sorry for my English, if you have not understood anything of the above I will gladly rewrite it.

[McGuyver]

Okay, I didn't realize it was a straight line vehicle. The 3V spark system does charge kinda slow, but I think it may need a different capacitor, like yours, to change the rate of discharge. Not sure, but yeah 12V would be better all around for your vehicle.

The way your tanks are mounted looks fine. Since almost the whole tank is in front of the engine the air rushing past it should keep most of the heat away. Also the fast discharge of propane out of the tank should cool the tank itself plenty.

priapo, Axt didn't say anything about this thing being slow, why would it be slow?:confused:

[priapo]

I mean slow when speed doesn't get to 70-80km/h, which is quite a good speed for such a small vehicle that doesn't seem to weight too much and doesn't have a good bodywork. If speeds are greater than 70km/h discard common tubeless bicicle wheels as they won't work too well.

Shell Eco Marathon's cars can get close to 85km/h (at least one of which I know) and it gets really difficult to control when it gets more than 60km/h and it has a really well designed bodywork, high quality amortiguation devices, armwheels, ....

[Axt]

Im looking at 100-150 km/h or killing myself trying, go-karts are easily capable of these speeds. You must remember the design was made not to just work well, but some things are sacrificed so it can be convenient to make. Therefore the front wheels are off a racing go-kart for easy steering assembly, back of a bike for easy breaking etc.. no point designing some super-car then not being able to make it.

Note that in the link I posted earlier its stated that a very crap go-kart with a less powerful engine was taken up to 100km/h.

And yep.. as I said, these tanks are likely to be exhausted within 5 minutes so they are more likely to freeze up then overheat from the engines. There is likely to be a heat shield behind the seat (not shown in picture) that will reflect a lot of the heat back onto the tanks but its still an unlikely problem.

[McGuyver]

I figured you were going for some decent speed. :)

Do you know what frequency that circuit will produce sparks? I would think you would need something pretty fast. I don't get how your going to control that or if you need to. If your looking for something constant there are better ways to get a constant spark. Maybe spark isn't even needed after the engine gets going?

[Axt]

The spark is just to start the engine, no need for it once its running. But since its unlikely to start first go, im guessing you want a fairly constant spark to help it hit its right beat


... fuck, I just dropped the bike on the engine and dented it....

[McGuyver]

Well if your looking for constant 10KV oil burner transformers are easy to find. They produce a spark about 1 inch long and it's constant. Try some air conditioning repair shop or someone that does air conditioning repair.

There are also neon sign transformers that produce 15KV. These are just made to power neon signs. These two tranformers if you can find one will light just about any fuel/air mixture.

[Axt]

12 volt? It has to be battery powered.

[Tuatara]

Oops. Silly me, forgot about the freeze factor with high drain on your propane tanks. Chances are you will have to heat the buggers to keep the pressure up! What are you going to do for a regulator? Ordinary propane tank regulators seem to be capable of only 2kg/hour throughput.

Forget neon sign trannies, or oil burner trannies. Primary volts too high. Use automotive ignition coil - they are designed for the job!

[McGuyver]

Yeah you would have to have an inverter to get 120VAC. Not to big of a deal if you want the constant spark.

Ignition coils aren't too bad of a choice they work off low voltage but their spark is way colder and won't light your mixture near as easily.

[Axt]

I'll go for the coil .. this way ill just incinerate myself as opposed to electricuting myself as well.

The tanks will more then likely be inverted to inject liquid propane, should be able to get enough fuel into it that way. It does sound dangerous but!

[McGuyver]

You know depending on where you do it you might have some electrical outlets nearby. You could reduce your weight quite a bit without all this starting shit. Batteries weigh a ton. You planning on doing this on some kinda track or what?

[Axt]

It would be quite impractical to have to plug the vehicle into a powerpoint to start it, its not like im after the land speed record. You could probably carry around a starting box containing the battery/air blower/ignitor circuit etc. but I really like the idea of sitting in the "cockpit" hitting some buttons and starting the engine.

As for the starting components, what I had in mind was a rechargable gell-cell battery and a 12v vacuum cleaner to provide the air, not that heavy.

http://www.absbattery.com/images/slapic.jpg http://www.iowa80.com/iowa80/images/S35747.JPG

[Axt]

Just a picture update:


http://ww1.altlist.com/~52497/rogue.altlist.com/images/jetstrike.jpg

[Axt]

Better picture:

http://ww1.altlist.com/~52497/rogue.altlist.com/images/jetstrikeside.jpg

The back will be built up more with engine mounts, heat shield etc. but that pretty much shows the scale of this thing. While a fibreglass body would look nice, I think the possibility of needing a quick exit rules out that.

[Mr Cool]

Nothing to say, except that it's looking nice so far!

[McGuyver]

Looks awesome but it appears that the whole rear assembly is like off center? You are still planning on two jets right? If you really want to get some decent speed I wouldn't think you'd want more thrust on one side of the vehicle pushing it to the right or left. Maybe it won't make a huge difference but it would seem better to have everything lined up, maybe I'm just seeing wrong.

[Tuatara]

Looks as though that engine is untested. (no heat marks!) Don't you think you should do a static test on the engine before leaping into building a complete cart? It would be sad to have a flaw in the engine ruin your vehicle on the first run. It would also be well worth measuring everything you can on the running engine - thrust, center of thrust, thermal, fuel consumption rate etc... Something may come up that requires a change in the overall design. (I speak from my years of experience as an engineer:D )

[Axt]

Actually none of the back end is even mounted on the frame yet, hence its off centre look. I still plan to have everything centred with twin engines flanking the rear wheel, though im unsure if the engines will be independant of each other or joined through the combustion chamber.

To take static/thrust tests I would still have to build a wheeled platform with engine mounts - which is about all ive done thus far anyway. Im sure to test one engine first to make sure its correct before worrying about the second.

[Axt]

Its getting there ..... slowly.

<img src="http://ww1.altlist.com/~52497/rogue.altlist.com/images/jetstrikef.jpg">