New way of building a valveless pulse-jet: integrated intake

[metiz]

I just got back from testing a new engine. It's based on a 4/5 pound Laird chinese with a couple of heavy modifications. The choke cone has been removed. In place of this, there is a 2nd cylinder, wich in this case is the same D and length of the combustion chamber. After these 2 cylinders, there's a small choke with the sole intention of reducing the pipe back to the rectifier D

The intake is where it gets interesting. It has been integrated inside the "super choke" (2nd pipe) to act as the compression/ restriction device or what the choke cone normally does. The outside of the intake acts as resistance. The intake is positioned in the centre of the super choke and faces the dome of the combustion chamber. It is free floating so no metal can get hot enough to desintegrate. The cold air flowing through the intake should be just enough to prevent it from breaking down.

I tested it and it runs (starts as easy as a normal engine) but only on forced air. When I got back from testing, I notices that the injector was pointing towards the wall of the intake and not straight down, so that might very well have been the problem.

Other theories are:

The combustion chamber starts functioning as part of the acoustic length in the same was as my pipe jet did. To solve this, i might need to shorten the tailpipe

The injector might have been off, other then being positioned wrong, The Rosscojector could have been to tight or to far/ not far enough positioned inside the intake.

The intake is not giving enough resistance to alow for enough compression. To fix this, the
super choke could be reduced in D.

As you can see in the photo's, the actual intake still sticks out quite a bit. This has been done simply to make my build less challenging. It could very easily be made so that the flare is flush with the super choke, appearing as a simple hole. This could be usefull in reducing drag in possible flight engines. It would also leave room for a small augmenter withouth increasing the drag a whole lot more then a traditional intake would have done.

Please ignore the shoddy welds.

I can't disclose the dimensions yet since it has been based on an engine that has not been designed by me. I aslo do not know if they have been published. When and if I get permission to post the dimensions, Ill do so.

Leave some feedback, suggestions or improvement ideas.

[Eric]

I would shorten the combustion chamber, and use a domed cap with the center pushed into a spike shape, and lengthen the center tube.

I still think that if you get it running at its full potential, its going to melt unless you use a fuel like methanol.

Will be interesting to see how it turns out.

[metiz]

I would shorten the combustion chamber, and use a domed cap with the center pushed into a spike shape, and lengthen the center tube.

I still think that if you get it running at its full potential, its going to melt unless you use a fuel like methanol.

Will be interesting to see how it turns out.

Can you elaborate on the changes you are suggesting?

[PyroJoe]

Would be interesting to see the internal configuration of the intake. Curious how performance will compare to a well designed augmenter?

[metiz]

Would be interesting to see the internal configuration of the intake. Curious how performance will compare to a well designed augmenter?

the .gif drawing, although not to scale, is pretty much how the intake looks. It might give a slight increase in thrust due to better mixing but it will most likely not compare to any augmenters bolted on a traditional Laird engine.

[PyroJoe]

Ah, thanks, missed the .GIF (below the third picture)

[Mike Everman]

Rossco did a bunch of work on linear versions like that. Cool. Though I like the idea, I think the exhaust can be larger diameter than normal confinement ratio thinking, since it's tough to push gas out that intake. As you know, it's very much about getting the gas out in a hurry, to make the lowest partial vacuum for the next cycle. Faasssinating

[Eric]

Well from your drawing, the space around the intake and behind the intake will still want to behave as a combustion chamber volume, filling with fuel air mixture ( if the chamber is shorter) otherwise it could potentially just be a big 'dead air' space that has hot non combusting gases that sap the energy from the combustion pulse as it is transmitted to the exhaust expansion.

I would make it so that the intake is near the combustion chamber dome, so that the air comes out, splashes off the dome and fills around the intake and back to the choke cone section, with the chamber cap being a shape to help the flow hitting it curl around and flow smoothly.

In some designs turbulence can be a good thing, but in small laird type engines you want things to be pretty smooth, since the rear facing chinese type intakes are at a disadvantage as far as chamber filling.

As a result of shortening the chamber, you would probably want to make it fatter since the intake would be taking up a portion of the volume. I'll sketch something up in paint. Also dont be afraid of long tailpipes, too short and they wont properly harness the combustion chambers output.

[metiz]

Ok I fixed the injector problem and tried again. I also tried a thrust reading but the sun was shining on the display so I can't see shit on the video. fantastic.

Anyway, I've got a small vid of the engine running. It starts a lot easier, I had throttle controll and all but still no sustained run. So out of the modifications suggested, what would be the best idea to start with: decreasing CC size (with pointy endcap) or increasing rectifier length?

[Thor]

Ok I fixed the injector problem and tried again. I also tried a thrust reading but the sun was shining on the display so I can't see shit on the video. fantastic.

Anyway, I've got a small vid of the engine running. It starts a lot easier, I had throttle controll and all but still no sustained run. So out of the modifications suggested, what would be the best idea to start with: decreasing CC size (with pointy endcap) or increasing rectifier length?

Greetings Metiz and the rest of the board.
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Straight to business:

After watching your recorded video I noticed a immediate glow right at engine start-up on the bottom mid way down the CC-Choke section (Right at a seam weld by the looks of it).

Could it be possible that a hole has burned through there and acted as one factor for the engine not sustaining?.
Might want to check that.
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Just my two cents worth.
Cheers.

*PS: Great build

[metiz]

Could it be possible that a hole has burned through there and acted as one factor for the engine not sustaining?.
Might want to check that.
Cheers.

Nope. thats my wooden skateboard starting to glow from the radient heat

[metiz]

Whats that? "try shortening the CC and putting a modified encap of first"?
Sure thing!

[metiz]

Ok I modified the engine and tested it again. same result. I have a vid but not uploaded it yet
When I returned home on my gokart, I was greatd By a farmer that has his buisness pretty close, telling me that I had upset his cows and that if they produce less milk, I'm getting the bill. I REALY REALY hope nothing comes from it, otherwise I'm royally screwed. Didn't help that a freaking helicopter flew over his farm at 150 meters 2 minutes after testing, either.

Anyway, any other suggestions I can try SOMEWHERE ELSE when this blows over or when I'm bankrupt?

[Eric]

Got a picture? What mods did you do?

[metiz]

Got a picture? What mods did you do?

Thanks for the reassuring words

I cut off about 25mm from the back of the cc and replaced the endcap with a concaved inwards one, 23mm.