What is a pressure jet?

[Viv]

What is a pressure jet?

Let me just state quite categorically and unequivocally that the pressure jet is in fact a valveless pulse jet

I know! I am committing the worse kind of heresy but the fact remains that it is a valveless pulse jet! weather you like it or not, it is a none steady combustion device.

Intermittent combustion taking place in a engine designed and constructed to be resonant, well we normally call that a pulse jet now don't we!

You may like to think of the engine as a Logan/Chinese combustion chamber with a pressurized fuel system, thats not the complete story but its enough to characterize it for you.

Viv

[luc]

Hi Viv,

THERE .... YOU GO AGAIN ... He he he ...

What the hell does it matters what type of engine this thing is.

For me, pulseJet, pressurejet, valveless jet ... They are all the same.

All those are God damn engines that burn huge amount of fuel, produce heat and thrust .... That it.

Hooo ... By the way my dear old friend ... Don't be to convinced about your "None Steady Burner" theory. When I have tunned engine #4, and was playing with one of the stage and I saw something radder strange, that I will investigate more, while tunning engine #5.

If you remember the osciloscope graphics pictures posted when the engine was delivering thrust, you could see an oscilation that goes from 0 to 130 pnds of thrust. That's the engine normal pulsation frequency and it seem the engine push and release, push and release. This is were the "None steady burning" come from. It pulsate.

Welll ... It seem from what I have seen on my last engine tunning, that depending were you located one of the stage, the engine change from a pulsating engine (from no thrust to full thrust) ... To a less pulsating state
(i.e : from 60 to 120 pnds aprx.)

What I mean by that, is the pulsations peaks flatens and the engine never drops its thrust to the 0 mark. What you see on the scope is a more even and less oscilation. Of coarse, the price you pay for that is in thrust figure, but the engine get smoother and the burning is always ON.

But again ... I need to bring a picture of that for you guys to beleive me ... And I will. The reason I did not pay attention to it before, is because I was to focused on thrust. So ... I did tunne the engine to 130 pnds, over shot my adjustment, saw this fenomena but braught the engine back to 130. It is only after that I realised what I saw.

He he he ... I can Imagine Viv now ... Going Bursurk and saying "Why the hell did'nt he tell me that before" .... Ouuupsssss .... Sorry Viv ... Forgot ... he he he.

Bye the way Viv.... Sorry for the Bomb in your camp ... he he he.

Cya Budy

Your friend

[Viv]

Hi Viv,

THERE .... YOU GO AGAIN ... He he he ...

What the hell does it matters what type of engine this thing is.

For me, pulseJet, pressurejet, valveless jet ... They are all the same.

All those are God damn engines that burn huge amount of fuel, produce heat and thrust .... That it.

Hooo ... By the way my dear old friend ... Don't be to convinced about your "None Steady Burner" theory. When I have tunned engine #4, and was playing with one of the stage and I saw something radder strange, that I will investigate more, while tunning engine #5.

If you remember the osciloscope graphics pictures posted when the engine was delivering thrust, you could see an oscilation that goes from 0 to 130 pnds of thrust. That's the engine normal pulsation frequency and it seem the engine push and release, push and release. This is were the "None steady burning" come from. It pulsate.

Welll ... It seem from what I have seen on my last engine tunning, that depending were you located one of the stage, the engine change from a pulsating engine (from no thrust to full thrust) ... To a less pulsating state
(i.e : from 60 to 120 pnds aprx.)

What I mean by that, is the pulsations peaks flatens and the engine never drops its thrust to the 0 mark. What you see on the scope is a more even and less oscilation. Of coarse, the price you pay for that is in thrust figure, but the engine get smoother and the burning is always ON.

But again ... I need to bring a picture of that for you guys to beleive me ... And I will. The reason I did not pay attention to it before, is because I was to focused on thrust. So ... I did tunne the engine to 130 pnds, over shot my adjustment, saw this fenomena but braught the engine back to 130. It is only after that I realised what I saw.

He he he ... I can Imagine Viv now ... Going Bursurk and saying "Why the hell did'nt he tell me that before" .... Ouuupsssss .... Sorry Viv ... Forgot ... he he he.

Bye the way Viv.... Sorry for the Bomb in your camp ... he he he.

Cya Budy

Your friend

Jeez you guys would just not believe how hard it is to collaberate with a canadian! every thing is a bleeding secret till you work it out for yourself when they proclame "oh didn't I say?"

Yes I fully expect the cycle to flatten out as it gets better at burning Luc its all part of the theory of operation!

Viv:-)
Ps oh did I not say why I thought so!:-)

[Mark]

Luc,
That was interesting about the stair-stepping nature of your Gluhareff. And Viv, that was interesting about the sheet of plywood affecting thrust levels from 2 feet away was it?
Mark

[Mark]

I wonder how a Logan compares to a Gluhareff thrust and fuel-wise? I read in Foa's book that there has been no better method found for mixing air/fuel than that of a side-ported Logan? The two engines seem to be cousins in most respects.
I wonder if a really large Logan would be tempermental or if it would be happy to go up and down the entire thrust range without the stair-stepping qualities of the Gluhareff and the melting of the 2nd stage if not careful. Seemingly, a Logan would be easier to tune and to make.
I have only toyed with a small Logan, but it really tickles me how peppy/loud this primitive little valveless is, with a combustion chamber made from 3/4 inch diameter plumbing pipe. It can go from a dead silent zero to full grease instantaneously, if I use methanol.
In this picture it is running on acetylene, and I could slow it way down or bring it up to a high pitched whine, by turning the knob on my acetylene/oxygen torch tip.
Finally, I wonder how super-heated fuel at a high velocity would affect a Logan, or if a typical room temperature fuel-injected substance such as gasoline would fare just as well? There's that weight penalty of having heavy fuel tanks if you are propaning it and flying.
Mark

[steve]

After staring at that picture for awhile I now have an overwhelming desire to build one. Could you tell me what pipe components you used?
I still don't have a summer job so anything that you can give me to play with (to prevent boredom) would be much appreciated!

[Mark]

Well the basic pieces are:

1. The tail 12'' section of 1/4" diameter plumbing pipe
2. The bell or neck 1/4" to 3/4"
3. The combustion chamber a whopping 3/4" diameter by 4" long
4. The side port 1/8" diameter plumbing pipe by 1.25 inches long
5. The head either a 3/4" cap or a 3/4 bell reducing to accept a spark plug or methanol fuel line if you go that route.

For the side port, you will need to drill a hole and tap it with a 1/8" NPT tap, it's a very common tap found at most hardware stores or in tap and die sets at Sears, auto stores, etc. (national pipe thread = NPT I think) The smaller spark plugs will screw into this threading nicely too, ones such as the CM-6, (10 mm) if you later want to use your side port for a spark plug.
I used some silicone tubing for the gas to flow through and then cut a tiny piece of very tiny copper tubing for the fuel injector. The side port gets a tiny hole drilled in it very near where the side port screws into to body. The hole is just big enough for the tiny copper tubing to fit snuggly into and flush with the inside of the intake port so as not to interfere with the in/out flow. With gaseous fuels you will need a spark plug. If not you will only get blow torch action out the tail, it's nearly impossible to get the flame to charge down the tail to light the combustion chamber. I used an air compressor too to puff in air at times assisting starting.

I was never successful using propane, however MAPP gas did OK and acetylene is down right a breeze to start it up with. With methanol, I had to angle the jet like in this picture of it running cool blue and I only had enough methanol in the tubing for short runs. Hot humid weather makes methanol a poor choice, wait till it gets cooler if you want to go that route.
Mapp gas is available at Walmart or most any store that sells propane canisters.

All the parts are pretty simple to make or come by comparatively. Really, you only have to drill a hole and tap it. And the 1/8th inch side port you will have to cut to length and smooth the insides so it doesn't have an internal lip if you cut it with a pipe cutter or hacksaw. Drilling the tiny fuel hole is nothing much in effort, a 1/16th inch drill bit should be about right for that.

The last two ingredients are patience and sensitivity. You will have to find the right fuel flow and accept a failure or two before it "starts right up."

Here's some cheap 10mm spark plugs but you can also find similar ones at Lowe's, Home Depot, or in various stores that sell small gasoline lawn care engines.
http://www.ngk.com/more_info.asp?AAIA=&pid=3291

In this picture I used a fly tying clamp to hold the tiny copper tubing and just positioned the copper fuel line flush at the tip of the side port and 90 degrees to the intake/exhaust. I filled the tubing by spraying in several pumps of methanol until the clear tubing was full. Methanol gets pushed from the tip of the jet over to the side intake port when it starts up. With a prime you can start it by just lighting the tail. It runs for about 10 to 15 seconds this way, it was just something that worked. The fuel is sucked in the side port around the edge even though the exhaust would seem to make you think otherwise.

You can see the faint blue flame of methanol as it is running loudly.

[Mark]

The MAPP gas set-up, ..... maybe you can get propane to work, I felt I could have with more work and patience, if you could figure a way to pre-heat the propane fuel line first perhaps. I got the fitting off of a camping stove made for propane.

[steve]

thanks for the info!
by the way, how did you work out the dimentions for this thing? did you calculate it or did you use the TLAR method? (that looks about right)

[Mark]

Yes, I used the acronym TLAR, the CAT method, (cut and try), and the forever popular KISS adage. A few years ago these 5 easy pieces, little pipe fitting parts were only a few dollars each from the hardware store.
I had reved it up many times with methanol sprayed onto the inside walls, but left it on the shelf for several years and only took to actually running it with a gas tank of some sort recently.
It makes an interesting sound, I don't know how to post sounds but if you would want to listen to it, I can email you a short sample. Every so often when I am in the garage I spray a shot of methanol in it, (no fuel tank), and then just light the tail with a lighter just to hear it rev up for a short second or two. It's just interesting to listen to it go from zero to full grease so suddenly. It is by no means optimized, but the decibel level is enough to startle any unsuspecting onlooker. You would want to wear muffs if you ran it for any length of time.
Mark

[steve]

Those components are EXPENSIVE!
2.50 for an end cap is robbery especially when you considder it only costs a few cents to manufacture the stupid things

the real problem is that none of the hardware stores around here even stock 12 inch lengths of quarter inch pipe. I had to connect two 6 in. lengths. I also couldn't get either of the connectors on the ends of the combustion chamber because they are aparently exotic parts for the crappy hardware stores.
curently I am trying to figure out how I will attach the spark plug without the right components. I'll get it eventually and post pics if it runs.

[Mark]

If you want, you could start with a common 1/2 inch pipe and use some larger size such for a combustion chamber, those fittings are everywhere. I made another crude Logan with strange proportions. The tail pipe was 3/4 and the combustion tube 1 1/4 inch and a very small/short 1/4 inch side port. Perhaps a 3/8ths or 1/2 inch side port would work too.
You can cut and try, but the larger sizes are even more expensive. If you look around you can find some industrial supplier for these parts. Or perhaps you can come up with your own design from some other pipe pieces. The nice thing about them though is that they all screw together.
I've always wanted to make a pulsejet out of that common copper tubing and connectors. Some copper connectors are made with pipe threading at one end. You would get a pretty green/blue colored flame using copper. It's neat to see a flash of dazzling color out the tail pipe.
You can see the 1 1/4 inch diameter Logan at the bottom of the wooden stand on the floor. The exhaust tube is 3/4". I put a little tail bell on it which seemed to help, perhaps because the exhaust tube was a little short, it added length. I just used what I had.
Mark

[steve]

It's Done!!!

There are a few diferences but I think it is close enough to your version to run well. I'm especially proud of the endcap/sparkplug. While everyone else was watching fireworks, I was welding. I probably saved about five bucks too, because I used stuff that I already had rather then getting a tiny sparkplug and an "exotic" bell.

I will test it tomarrow and hopefully post some pics of it glowing.

[Mark]

Not a bad likeness! Your side port fueling looks better than mine. Be sure there are no lips on your pipe especially on the tail end, in fact you could drill or flare it with a drill bit so inflow is smooth.
If you have a bottle of HEET, (methanol) and a finger pump sprayer, you can just coat the insides and light the tail end with a lighter, it may rev up if it is not too humid. I had a hard time with propane, but MAPP gas worked with some gentle tweaking and puffing from an air compressor into the side port as the gas is flowing.
The tail pipe might be a bit fussy with a connector, but I hope you have good luck. The little guy can be finnicky; I and Gary in Australia found that it helped to angle our valveless puslejets about how I have it in the vise, for some unknown reason it likes this angle best for starting, tail up somewhat.
You're in the ballpark.
Mark

[Mark]

One other thing is that I put the jet in a vice and snug up all the parts, you can test to see if it is air tight or leaky by blowing in the tail covering the side port with your finger. Plumbing pipe really has to be tight to seal well enough. Small jets are really sensitive to leaks. A hand and a wrench aren't enough, you will need to vise tighten it or use two wrenches at the same time. May the gods of feedback be with you.
Mark