Running a no-weld pulsejet

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GRIM
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Re: Running a no-weld pulsejet

Post by GRIM » Tue Sep 01, 2009 11:47 pm

Butane is not so bad , it gets a bad reputation because the pressure drops to pretty well zero in cold weather and usually comes in very small containers , think disposable , these really are of little use to pulsejets , especially of the size engine you have there ,

I agree with Simon try a rosscojector , cheap and not so nasty , he refers to lighting the rosscojector THEN insering it in the hole, this Sometimes works with valveless , but i have my doubts it will work with a valver,

I also agree with Simon about a piece of tube about the same size as your cc diameter and form a venturi using clay or firegum , both will work ,

Rule of thumb for the venturi diameter is area < the sum of the area of the valve ports,

Any large supermarket will have a whole range of potential venturi devices , they look like salt and pepper shakers sometimes , other times they are disguised as metalic flower vases , sneaky little suckers , :lol:

The soft soldering I was refering to was for a fuel injector /metering device , I will try to take a better photo of what I have so you can see what I mean,

James OS
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Re: Running a no-weld pulsejet

Post by James OS » Wed Sep 02, 2009 8:57 am

Ok, I'll put together a rosscojector and try another run with the butane (Summer here looks about the same as Winter, so I may also have to warm up the tank).

I'll also put together a venturi like you say from some cups or shakers or something - will any thin tube work for the venturi to work? I've got plenty of 0.6mm thick tubing.

This is the intake I was talking about - any chance of that working???
They're not in focus - camera's battery was about to run out...
IMG_0065.JPG
IMG_0067.JPG
Ok rosscojector is now on - but it's pouring with rain...
When it stops I'll give it another shot with gas.

GRIM
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Re: Running a no-weld pulsejet

Post by GRIM » Thu Sep 03, 2009 2:23 pm

Hi James , the ventri looks good ,
have attached a couple of photos an a pdf , this should give you an idea , very crude , but works ,
the flow control is something you will have to find , there are many different types , pretty well any of them should work, you just need some way of adjusting the mixture, and this is very important , just a couple of turns makes the difference between a runner and non runner,
the threaded rod is just a fixing device , you could use anything , think mole grips , or something
hope it helps
Attachments
fuel metering.pdf
(7.89 KiB) Downloaded 348 times
IMG_1256 (Small).jpg
IMG_0776 (Small).jpg

James OS
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Re: Running a no-weld pulsejet

Post by James OS » Thu Sep 03, 2009 4:38 pm

Ah, I see...
Thanks, Grim. I should be able to solder together something along those lines - I'll run my jet again this weekend and post the results.
Again, many thanks for all your help.
James

James OS
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Re: Running a no-weld pulsejet

Post by James OS » Sat Sep 05, 2009 2:51 pm

Tried the gas again - it ran out before I could get a proper run in. I'm now focusing on a venturi.

I drilled two 1mm holes in a short aluminium sleeve - this fits in the base of the venturi. For a flow regulator I used a cheap radiator off cock which fits snugly into the top of a water bottle - I'm hoping this won't dissolve. A hose will fit onto this and connect it to the sleeve - this should allow some flexibility if I want to move the fuel bottle.

I also forgot to ask - why did you put a copper tube inside another tube? (Sorry if the answer is blindingly obvious).

Anyway this is how far I've got (please tell me if you think it hasn't got much of a chance) :
Gas off-cock.jpg
The black bitumen-like stuff is leak sealant
Venturi 2.jpg
Venturi.jpg

GRIM
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Re: Running a no-weld pulsejet

Post by GRIM » Sat Sep 05, 2009 3:54 pm

Hi James ,
The venturi looks good ,
I am not too sure about the tube sticking in the side, I tried various versions of this, IT SEEMS A GOOD IDEA , but I couldnt get it to work well ,
heres a pic of how I set the fuel metering device in the venturi , ie axially down the centre line ,
you asked about the tube inside a tube , this was more than anything just so that the various diameter fittings that I had would easily fit together I am sure one tube diameter would work ok ,

The idea is to blow compressed air down the tube with the blue plastic on it , this creates a negative pressure in the fuel tube as the air flows over the holes , thus drawing fuel up the tube from the fuel tank , once running the venturi effect creates a similar low pressure , thus no need to pressurize the fuel , and the compressed air is essential to open the valves to allow the fuel air mix to enter the cc

I worry about your water bottle , please try to find a small metal container , I used a brake fluid tin , maybe a coffee can or something , LIQUID FUEL IS DANGEROUS , you will quite likely have some "unexpected events" i did, everyone does, make sure you got a fire extinguisher at hand and some old towels soaked in water to smother any little liquid fires before they become big fires ,

You are on the right track with the radiator valve , but I think it will be too coarse wrt control , an alternative is to use a small clamp on a piece of flexible tube , mole grip , or similar , that way you can have fine control of the fuel flow ,
Attachments
fm (Small).png

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Re: Running a no-weld pulsejet

Post by James OS » Sat Sep 05, 2009 5:35 pm

Ok, I can get hold of a metal bottle and maybe buy/make something to control fuel flow finer - a hoffman clip or something similar perhaps. I'll mount the venturi axially like yours - I just thought most people used a tube from the side.

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On the right track?

Post by James OS » Sun Sep 06, 2009 2:39 pm

Ok - here's how i'm doing - what do you think?
Axial Venturi 1.jpg
New axial fuel pipe setup - air will have to come from a manually aimed tube.
New fuel tank 1.jpg
Empty wood stain can - used to contain petroleum-based solvents. Off cock used as a hose connector and can still be used to cut fuel flow.
New fuel setup 1.jpg
Just found the old mole grip - I'll use this as a fine control

vturbine
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Re: Running a no-weld pulsejet

Post by vturbine » Mon Sep 07, 2009 3:21 am

Looks scary to me, man.

I don't like the plastic hose anywhere near the engine with gasoline in it. I'd want to see a few feet of metal tubing at the inlet end. Maybe that's just me. If you break a valve, and or flood the engine with a leak, and it's hot, using gasoline. I don't know. Who knows what all the possibilities are -- I don't.

Just don't like it.

You know, nobody is going to be able to tell you something is "okay" or safe to do. And it's even unlikely people can spot every problem for you, and also not their responsibility to warn about what they personally would be uncomfortable with that you are trying.

Don't get me wrong, I'd really like to see you be successful in making a pulsejet. But I personally wouldn't feel comfortable with what you show at present.

Also why a gallon, instead of an ounce or two?

That's rhetorical -- I don't need or want an answer. You need to ask yourself safety questions and imagine unforseen problems and scenarios yourself -- that's where personal responsibility comes in.
No problem is too small or trivial if we can really do something about it.

Richard Feynman

GRIM
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Re: Running a no-weld pulsejet

Post by GRIM » Wed Sep 09, 2009 2:54 pm

Hi James ,
Sorry for not replying , been busy , I too worry about the garden hose , that stuff is not suitable , its not fuel proof , and please do try to find a small can , about the size of a soda can would be good 250cc or so, and they are best not sealed , apart from the fact that you need to allow air to enter (breather ) it is safer to have them open to atmosphere , worst case they just burn in a contained fashion , not explode,

Let us know how it goes :D

Mark
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Re: Running a no-weld pulsejet

Post by Mark » Thu Sep 10, 2009 12:24 pm

I made a lifting device using parts from a camera tripod to elevate a plastic PET bottle of fuel to the right level. It has a little crank handle and locking feature. With the store-bought Dyna-jet, the instructions say to bring the fuel level about a third of an inch from the metering jet. With clear tubing you can see what's going on with your fuel or if you have any bubbles in the line. A few times I have started a fire in the throat of a Dyna-jet or my homemade valved pulsejets. If you have a damp cloth ready you can plop that over the fire before your fuel line melts.
Once you start puffing in air you can watch the level of the fuel get drawn into the metering jet or getting pushed back down the line. On homemade jets I have on occasion mistakenly designed the metering jet and/or air injection method and instead of drawing in fuel, the fuel was driven back down the line. In this respect, it is helpful to see what the fuel flow is doing so you can associate this with what sounds the starting engine is making.
For gasoline I use Tygon fuel line and silicone fuel line for methanol, which is far more forgiving in the rich or lean department. Tygon is yellow but you can still see what the fuel is doing.
http://bonzisports.com/catalogue/images/fuel.line.jpg
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vturbine
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Re: Running a no-weld pulsejet

Post by vturbine » Thu Sep 10, 2009 9:10 pm

Garden hose is generally 1/2" to 3/4" in diameter. The green braided vinyl is usually 1/2" ID.

My full size John Deere Model M tractor uses a 3/16" ID gasoline fuel line with a gravity feed of a few inches. Green braided garden hose is 7 times that ID area. I doubt the Tygon line is much more than my tractor's fuel line ID, as well. The extent of a leak (and likelihood of a leak, as well) of a Dynajet using proper sized fuel line is considerably less than the danger of a gallon can of gasoline connected by a garden hose and glue to a homemade jet of this sort.

I think a small can connected to some flexible tube of proper diameter and then enough length of metal tube to the inlet to give good thermal separation from the engine would worry me less than the present setup.
No problem is too small or trivial if we can really do something about it.

Richard Feynman

Mark
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Re: Running a no-weld pulsejet

Post by Mark » Fri Sep 11, 2009 2:11 am

I agree the garden hose is a bit large in diameter. I have about 50 ft of silicone tubing that is 3/4 inch inside diameter and several other diameters I bought on eBay. The smallest is about the width of spaghetti. I have 3 or so "normal" sizes of Tygon. But I suppose if you use the large diameter tubing you could do away with the fuel tank and just use the hose for a tank. ha
I once thought of using a meter of my thick-walled (19 mm inside diameter) quartz tubing as a fuel tank in the verticle position.
One time I used a way larger than necessary tubing/fuel tank for my little Logan and developed the most interesting fuel hammer effect where the pulsejet would rev up and down instantly and erractically like a scalded duck quacking. That was the funniest sound I ever heard out of a pulsejet. Strange what can come about when you are just tinkering.
At many auto parts stores you can buy neoprene tubing in several sizes/selections if you wanted to scale down from the garden hose. Here's a few of my silicone colors. I had to laugh reading an old post, Mike said he liked the hot pink color, although it is "so two-hours ago"/out of fashion now. ha
To digress, here you can see how the air pulses from the engine drives the fuel into the side intake where it is ingested. This size tubing/fuel tank produces a steady high-pitched whine whereas a fatter tubing made the fuel hammer effect that was so dramatic. That little bit of tubing filled with methanol would run the jet for about 10-15 seconds. You can't really see the alcohol fire but it is running loudly in the picture. I also ran the little Logan on MAPP gas and acetylene with a CM-6 spark plug in the tip instead of the pressure feed brass fitting.
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Re: Running a no-weld pulsejet

Post by vturbine » Fri Sep 11, 2009 5:44 pm

Mark wrote:I agree the garden hose is a bit large in diameter. I have about 50 ft of silicone tubing that is 3/4 inch inside diameter and several other diameters I bought on eBay. The smallest is about the width of spaghetti. I have 3 or so "normal" sizes of Tygon. But I suppose if you use the large diameter tubing you could do away with the fuel tank and just use the hose for a tank. ha
Hey Mark, that just reminded me of Free Flight model planes where duration was limited by using thick tube as a tank. :)
No problem is too small or trivial if we can really do something about it.

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Re: Running a no-weld pulsejet

Post by James OS » Sat Sep 12, 2009 7:06 am

The 5l tank and short aluminium sleeve are now gone - I've now got a metre of copper tubing and a small coffe can - I guess that was pretty stupid of me :D .

Actually - do you really think I could just use the hose as a fuel tank? If so it would save me alot of trouble.

The garden hose was all I had - remember I've only read about pulsejets, so go easy on me if I get loads of things wrong. I never realised liquid fuel (I'm using parrafin oil now) was so much more dangerous than calor gas - so far I've never used either for anything prior to this... No worries though - I'll take any suggestions on board.
I'm also trying not to get carried away with getting this thing to work, and remembering that I don't want to barbecue myself and my dad (who has actually been the safety inspector throughout this project - understandably he won't let me use real petrol/gasoline)
Cheers

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