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A DIY Mini Pulse Jet Engine
The valveless pulse jet engine or pulse detonation engine is the most simple type of jet and is therefore popular among hobbyists as a DIY project. it is often referred to as a 'tuned pipe' because its operation depends upon making the parts the right size and shape so that it fires, or resonates at the engines natural, fundamental frequency. This type of jet propulsion does not need any type of turbine, turbofan, or propeller, making it much less complex than a typical turbojet. In a turbojet the turbine or turbofan is used to compress the fuel/air mixture in the combustion chamber so that it is more efficient and powerful.
This jet engine has absolutely no moving parts and it relies on the simple shape of the combustion chamber and exhaust for it to function. The fuel to the jet is provided at a constant rate, but it is detonated in pulses. After each explosion there remains a lower pressure area inside the combustion chamber. This is immediately filled as air rushes back in and mixes with the fuel feed ready for detonation again.
This example of a homemade jet engine is about as simple as it gets, but it could not be used for propulsion purposes because it is only safe to operate for a short time. The main body of the pulse jet engine is made from copper pipes and various adaptors. The combustion chamber is made from two copper adaptors that have been cut and soldered together. Copper is an excellent thermal conductor which helps to spread the heat throughout the jet, but solder melts very easily so if the jet engine were allowed to run for more than a few seconds this part could come apart. This was enough to demonstrate the principles of operation which is all this DIY jet engine was designed for. If you wanted a working model for providing thrust, it would be necessary to consider different materials as a running jet will get very hot.
These images show the basic 'tuned pipe' without the spark plug and gas supply. Tuning was achieved by altering the length and width of the parts used. This was quite simple as there are wide range of plumbing parts that will easily fit together.
The fuel was provided from a cheap blow torch and was injected into the combustion chamber using fine brass tubes bought from a local hobby shop. This chamber also contained a tiny homemade spark plug. The spark rate could be controlled by varying the power to a HV capacitor connected in parallel with the spark plug.
The power supply for the tiny spark plug was made from a mini cold cathode PSU connected to a HV diode and capacitor. An alternative is to use an ignition coil and an ignition coil driver circuit.
The spark plug its self was just a single wire inside a small glass fuse. This wire was connected to one capacitor terminal (live) and the body of the jet engine was connected to the other terminal (earth). The spark would jump from the tip of the wire to the inside of the combustion chamber to ignite the fuel mixture.
The simple design and adjustability of this jet means that a wide variety of fuels can be used. The most common fuel used is kerosene and propane, but common lighter gas will work for this basic demonstration. Click here for More information on Jet Engines.
The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.
We replaced the large cone and connecting straight pipe with a cone shaped tube made from a rolled metal sheet cut from a large drinks can.
This improved performance and it would pulse nice and loud with a regular and rapid 'beat'. Unfortunatley the poorly constructed cone was soon destroyed. It may be better to use something more sturdy such as the metal sheeting available in DIY stores.
None of these parts were screwed in place. Some joints were soldered whilst others were simply crimped in place so that they could be adjusted.
To start the jet engine you must use some kind of air blower. For this example the outlet from a mini hoover from a PC cleaning kit was used.
I'm building a gas turbine aswell. Are u using a car turbo or are you building it from scratch?
For mine i'm going to use the turbo off a WRX the rest i will fabricate myself. I'm thinking of starting the engine on LPG then when it get warm enough switching to Kerosene just curious to know how far along you are with your engine.
IT has no curve and is a simle jet design.
please get back to me with some info on how to start it properly and or fix it.
I have just Added an image upload function to the comment forms. You can now include images in your posts.
When you say your jet has no curve, does this mean that it you are using a valve type system?
I was thinking of making the inlet bigger or repositioning the fuel inlet.
i'll send a pictuer when I get home from school.
Thanks for helping me with this.
I build the jet to get a better understanding of jet engine basics for example insted of narrowing down the combustion chameber and making the duct two tail plpe smaller i'll just make the two the same size and use a normal not narrowed chameber.
Your longest exauhst looks like it may be too thin. It might work better if it tapered outwards like a cone shape. This is also helpful for starting the jet as you can blow air in this end (not with your mouth!) to kickstart the pulses.
IT has no curve and is a simle jet design."
And i wondered if you could let me know how to make it or where the plans are.
thanx
Iain, Aitken91@msn.com
Just thought it would be a good idea to let you know how i'm getting along with my engine (everyone else thinks i'm crazy). I have done one successful test run to date on LPG an the engine has awesome power, the little bugger spools up like you would'nt believe and that was only at 60psi gas pressure (half throttle). The pictures I have included are the most recent of the engine and show my progress after aprox. 2 months. BTW nice job on you engine Justin just wondering if you have sorted out the problems you were having? Anyway, thats all from me,
Gene.
Thanks, Max
P.S. I'm 13! HA! Younger than ALL of you :D.
This is definatley not a jet you should make for propulsion as the materials used make it quite dangerous.
The best material is usualy steel as it is tough, and the parts can be welded together. You could also find many parts that can be screwed and bolted together, or you could make them youself if you have acces to bench machinery.
I must say though that a 13 year old kid with two homemade jet engines strapped to his bike sounds like bad idea. :O Whatever you decide to do, be careful! :)
thanx
http://www.vhp.co.uk/turbine/pulsejet.shtml
You are welcome to post links, but you must just paste the address (without any html code) as links are not automatically parsed (made clickable) because this would make us prime target for spammers.
can rmc please give instructions on how to make your spark plug
When switched on the spark jumps from the tip of the wire to the jet casing.
From what i've read about valveless pulse jets they seem to run off a concept known as "resonant frequency." This means that the speed of the explosions ie. the amount of detonations per second, has to be close to the frequency at which the jet pipe naturally resonates when you tap it with something. Looking at you engine i see that you have two 90 degree bends. Unfortunately not only will this impede exaust gas flow it probably also means that the engine will not run, and if at all only for a very short time - at which point the fuel mixture will become too rich and combustion becomes impossible. Also i agree with RMC, that gas you are using is not ideal. It is probably stored at a lower pressure that would be found in say a BBQ cylinder - and if that is for lighters then it will be propane, which is not as volatile as LPG (in my experience). Anyway hope i helped in someway.
Gene
I know u probably dont have the tools but i would also suggest round tube bent through 180 degrees with a pipe bender. It would also be useful if you have a system of sliding pipes so that you could change the length of the exhaut quickly, that way fine tuning will become way easier.
Gene
it took 5 hours hows that for customisation.
I wanted to thank you both and sorry i write too much.
The easiest way i can think of is to use what i used for my engine - two 90 degree exhaust pipe bends welded together should do the trick. Look in places that do car exhausts, the bends should'nt cost very much, if anything. That way you'll have smooth bends and eliminate any restrictions in gas flow. The only thing that might be a problem is the diameter of the pipe, the smallest i could find was 50mm ID, but you might be able to find something smaller, if thats what u need. Good luck
All I can say is HOLY CRAP!, dude that was fast considering the amount of work you put in. I'm 19 and at you age i could'nt even weld, that should work very nicely. Might pay to finish it off with the ajustable exhuast, if the engine dosn't run already that is. Good luck and happy i could help.
I couldn't say what the best way is, but the method used for the jet on this page was to feed in the gas via some thin brass tubing that was inserted through a hole in the combustion chamber
Unfortunately thats were my help runs out because i've never built a valveless pusejet before (Although plan to in the near future). All I can suggest is trail and error these things never work to an exact calculation especially with homemade stuff, i'm sure with a bit of mucking around with the engines different dimensions you'll get it to run. On the safety side can I recommend that if you cannot achieve ignition with a small amount of gas do not solve the problem with more gas - you know what will happen there! Just take your time playing with the amount of air you put into the engine when starting an pay attention to the ignition system (thats what gave me the most trouble on my engine). Anyway have fun.
BTW i'm sure you've been to this site but just in case -
http://www.aardvark.co.nz/pjet/mylockwood.shtml
thats the page where that project is located.
This may not make it on this site..but I believe that site maybe relevant to your viewers. If not sorry for even stopping by.......Be cool..keep it hot!!!!
mine starts for a while { couple of seconds} on low pressure and when i add gas it cuts out.
what should i do rmc?
Here are a few links that may help you figure out your problem. This page, Troublshooting PulseJets, is for the valved type but most of the principles still apply. You can also get a range of PulseJet Blueprints, but the preview links on that site seem to be broken, the download ones are ok though.
im worried the guy at the top will have the same problem. the tail pipe might be restricting air gas flow down the curve. could this be the problem? please help me rmc.
When making a pulsejet you will need to 'get a feel' for how different design aspects affect performance.
This page shows another DIY Pulse Jet Engine and shows the dimensions used for the pipes. It has a squareish U-bend with a relativle narrow diameter.
my hole jet dosent work.
i think this is due to the fact that the comustion chameber is too small.
Scroll past the stuff a the top to the silhouettes showing different designs. A few will have links below for more details.
by this imean dose it create the right sonic frequency.if so can you paste your dinamics
This one is very small in comparison and can be very difficult to get to run using just butane or propane. With some persistance it can be made to resonate at "the right sonic frequency".
A major drawback of this jet is that by the time it gets started it is allready quite hot, so the gas needs to be cut as soon as it begins to buzz.
Even if the solder joints did not melt, I don't think that this jet would self run contuously for any useable length of time as it was vey difficult to get it to buzz without misfiring.
With very small pulsejets it is often neccesary to use a more volitile fuel such as hydrogen. I've just been making a very tiny one, that will probably need Hydrogen fuel. I'll post it if I get it working.
and design wise.
can u if it runs paste the plans or meassurements?
Acceleatien would also be a good source of fule.
Notice the massivley over sized spark plug is the same as is used in the main jet example on this page. The graph paper in the background is 5mm to give you an idea of scale. The final dimensions may change so theres no point in posting exact details yet.
I'm wating to get the conical tailpipe made and I also excpect I'll need a source of hydrogen such as an electrolyser.
In regard to the fuel to use i'd recommend lpg first (because it is the cheapest and easiset to get). Don't even bother with hydrogen - you'll probably never make enough. If you need a really volatile fuel then Acetylene is your best bet like Joe also recommends. Hope i was of assistance.
15mm combustion chamber made from a section of standard copper pipe. Slits were cut in the ends so that the could be squeezed to make fittings for smaller pipes.
8mm air intake.
6mm Tailpipe.
2mm fuel pipe.
I don't know how wide the tail pipe will taper to yet, but it will just depend upon what I can get.
The fuel is injected into a collar around the air intake which may or may not help with the mixing of the fuel and air. The flow of the fuel should also induce air to flow in, allthough I think the low fuel pressure will mean that it doesn't make much difference.
The fuel pipe is brass, so I've bent it around so that it also acts as a stand for the jet
PS: Here's some data that may be useful to you guys. The upper and lower limits for the percentage of fuel in air to produce an explosion.
Propane
HI - 9.5
LO - 2.2
Butane
HI - 8.5
LO - 1.9
I got these numbers from a forensic report about a fire in a building. If anyone has figures for other fuels please post.
Gene:
I've not used LPG before, I'll probably try a few different fuels if I can't make enough H2.
Here's some more useful numbers. This shows the relative calorific values (in MJ/kg-1) of various fuels (data mostly from here);
Ethanol - 30
Methanol - 23
Diesel - 46
Petrol - 47
Kerosine - 47
Butane - 49.5
Propane - 50
Methane - 55.5
Hydrogen - 141.8
Making jet engines at home is very dangerous so you should think carefully about what you put together, and make sure you fire it up outside your house. Pulse jets often 'flame out' which is where a big fireball shoots out due to a buildup of fuel, or problems starting, so you must keep your distance from them.
If you want to build one, make saftey your number 1 priority.
Look i don't know if its my place here, and i certianly don't want to discourage anyone but don't you think 13 - 14 years old is a bit young to start playing with volatile fuels in confined spaces? I mean, obvious dangers aside, have you consided the skill and tools requied for such an undertaking? My advice start with something easy, learn to fix your bike, figuring out how a lighter works would also be a good start, after you've done that then you can build a "jet engine" - you're 14 right? Then there is plenty of time.
Has anyone played with using parts taken from brass musical instuments ... im thinking slide trombone ... as an engine chassis ? The even taper of the horn pipe, up to a bell, should make an awesome coupling for air pressures and provide lots of surface area for thrust. The finely machined tuning slides on these instuments may also be great for adjusting your effective pressure pulse frequency (pipe resonance) along with your fuel injector flow, to extend throttle range.
Any ideas or suggestions, as far as :
1) brass engine chassis
2) high voltage present on engine frame
3) intake / exhaust pointing downwards
any or all comments welcome ... thanx
A bull bar would be ok but only if it is steel. Most are aluminium so you might have difficulty welding it. Aluminium also has terrible heat handling capabilities it will expand, crack and deform under the high operating temps of a pulse jet. Glad to be of any help.
TURBO LEAKING OIL = PERFECT FOR GAS TURBINE
My turbo leaks oil from both the compressor and the turbine and it runs perfectly. I should mention that it is safe to start as long as the comp and turbine wheels don't touch their housings.
With larger pulsejets people often use a rolled sheet of steel that is welded at the edges to make your tapered section. This is not always practical though in smaller models.
It is more than 80 000rpm.
These are a few things I have that are in working order or never used :
-Briggs coil (Magneto)
-Chainsaw coil (Magneto)
-Chainsaw condenser
-Harley Davidson Condenser (Golf Cart)
many more...
I have heard of a "Buzz Box" such as the one in the picture, and dont understand how to wire it or something like it.
I have many more things to use AND the tools. Please tell me any ideas,plans, drawings, etc.
Thanks, Andrew.
You can see a few examples of circuits on the ignition coil drver page or the pulse controller page.
This can be very difficult in practice as there are many other factors (such as atmospheric pressure!) that can effect the flow of fuel.
The resonating sound from a pulsing jet comes from the resonant frequency of the air space inside. It 's like when you blow across the top of a bottle you hear a note that depends upon the volume of air inside. Less air = higher frequency. These tiny jets will have a notabley high tone.
Yes, I think a flared tail pipe should help the fuel mixture to reignite itself as it helps contain some of the hot exauhst. This hot exauhs must be sucked back in to detonate the fuel.
I'm still waiting for my tailpipe to be made, but it looks like its not coming. It looks like I may have to pay for it! :)
It does sound like you are on the right track, let us know how you progress with it.
This is similar to the pulse jet operation, but the fuel/air mix needs to be better so that it burns much faster (i.e. explodes)
Please be careful, and dont try making jets with fuel and plastic bottles.
because you need a capacitor to give a pulse
i need help so what capacitor?
PLEASE HELP
I have spent nearly 2 hrs. looking, reading etc. especially liked the links to both the "maggy muggs" and the " jet boat" projects....nice to see such creativity...just don't blow your collective A$$ up ;-)
Rochester, New York.
The glass is then inserted into a hole in the combustion chamber so that about 2/3 of its length remains outside.
This glass tube serves as an insulator so that a thick wire or metal rod can be inserted without it touching the metal body of the jet.
When the power is on, the spark jums from the tip of the metal rod to the nearest part of the jet engine casing.
It is glass, so it is fragile and will melt if your jet gets hot enough.
To convert 12V DC to a high voltage for a spark you will need an inverter of some sort. This project used a cold cathode tube power supply a HV diode and a small HV capacitor
A better method would be to use a proper ignition coil and a driver circuit.
I do have a bit of mechanical know-how, so I'm going to try a turbo engine for my next project. Does anyone know any good web sites on building a jet engine out of an old turbo?
But...
What about a bicycle, with 0 wheel hubs and road slicks? I've got a bike that one of these could be mounted on.... the way I see it, I could build the engine around the bike. And anyways, I'm going to be limited to what parts I can get from a junkyard; I don't have a welder and my budget is somewhere around 50 bucks.
Phil
to build pulse jet plans/blueprints
to get a jet engine to power a go kart u cant glue,paste,tape,etc. but on this site ifound jet engine plans that use muffler sealant http://aardvark.co.nz/pjet/noweld_pulsejet.shtml
hope fully this helps :D
im only 13 but this works really well for effects or braging rights.for fuel i used a 95% alchohal trate but u should use a lower grade (kerosene).And injcet the fuel in a mist.(sry about no pictures my computer wouldnt downlaod them??? have fun :D
I'll take "any" info you guys have.
Thanks; Keith
Thanks,
Spam
Usage of household kerosene as a fuel .. Pressurise the fuel tank. Preheat the fuel by coiling the fuel line around the exhaust to gasify the liquid kerosene. Allow the resultant gas to enter the combustion chamber through a fine nozzle.
Thanks..
Also the comustion chamber is cooled to a lower temperature from the outside container, therefore more oxygen is alowed in during the intake cycle at a higher density. Of course it would only work untill the water was boiled out, but would it work in theory or em I a retard ?
But you can try it... try is for free ...almost :D:D:D
On the contary though, a bigger tank with more volume + water would take longer to heat up. So lets say i have a heat source of x amount. It would take x twice as long to heat up 2 gallons of water then 1 gallon, also the water would evaporate twice as slow - thus less pressure. The less volume and water = more pressure - if that makes sence.
I didnt know about the water in gas form to water in liqued form ratio though. Thats actualy sounds pretty promissing, 1 / 220,000.
I am interested to design a valveless pulsejet engine of 0.5kg thrust can u suggest a method to estimate geomery of that engine
I have built and sucsessfuly ran two Gr-1's Four Gr-5 (turbo shaft) three pulse jet (one 15 feet 184 lbs of thrust)(two 6 foot) and a pen jet (realy cool "but realy hot")
Contack me @ Christopherkoen@yahoo.com
Hope I can help.
That looks like a reaction thruster for some kind of rocket. (I.E. That is a real rocket motor!)
Hey If you are working with fusion you better watch your ass that is verry unstable engineering your risking your life 100 fold of a pulse jet if your core cracks even if its a hair line!
1st question: Which material should i use to make pipes for this engine?
2nd question: Is there any proportions of thickness/lenght of pipes?
3rd: How big and long it have to be that the RC car can go about 60kmh (24mph) or a bit faster, remember that i would place a two of them and everything shouldn't be heavier than 5kg?
Sry for bad english, if it is :)
2,3. Yes. The dimensions of the pipe have to fit with the ferocity of the explosions. You'll have to figure out those dimentions yourself. You'll find some good info from others above.
this is all part of an experiment i am about to start, if your wondering...
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jet
obviously not completely to proportion. i can figure out fuel tanks. i can figure out putting a high powered fan in the top of it to get some start up for launch. just need help to put something like the engine in the picture at the top into a rocket. that will weigh no more than 20 lbs. so 50+ lbs would be preferred but enough to keep it moving without falling
They are typically made from steel. They are typically not used for vertical liftoff as they are not powerful enough.