Scrap Queen's first foray into valveless pulse jets

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ScrapQueen
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Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Wed Oct 28, 2020 7:08 pm

Hi folks, just joined and finally made my first jet. Been meaning to do one of these for *years* . Once I got to TIG in my welding class I knew what I had to do.

I made this fella without any real plans and just winging it. Its bad and poo.

Image

So next I made one off *actual* ratios from Pyro Joe's design.

Image

Image

The intake is real fugly, the intake pipe had some nasty stuff that smoked when I welded it that I forgot to brush off. Fingers crossed it runs! I'll be buying fuel system stuff really soon.

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Re: Scrap Queen's first foray into valveless pulse jets

Post by metiz » Wed Oct 28, 2020 8:02 pm

That's more like it! Did you sleeve the intake with a 2nd piece?
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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Wed Oct 28, 2020 8:05 pm

I did add a thin sheet metal sleeve and tack welded it around the bottom then did a small weld around the lip of the intake.

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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Mon Nov 02, 2020 3:46 am

I tried running my engine today! I think I got it to sort of idle I suppose. It made a low rumble and there was a flame pulsing in the bottom of the intake but no earth shattering roar or red hot chamber. It felt SO CLOSE to running! I ended up putting the injector about an inch outside of the intake and that got it to sustain its idle. It might not help that it was something like 35F outside today here in Minnesota :lol: . I don't have anything like a leaf blower or compressor which would be a big help I suppose. I don't suppose there's some way to start it that is cheaper than buying a whole cordless leaf blower just for starting it.

I'll try flaring the intake a little more and fixing the injector some more but I'm afraid without a compressed air source she won't start.

I'll upload the video of it idling when its done processing. It was a learning experience to see what might work and what won't.

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Re: Scrap Queen's first foray into valveless pulse jets

Post by metiz » Mon Nov 02, 2020 2:42 pm

What kind of injector did you use? A Rosscojector should be able to start an engine of this size without the need for compressed air, if you find the sweet spot. I'm looking forward to your video. If it's possible, also post a picture of your injector, injector setup and fuel delivery system.
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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Mon Nov 02, 2020 3:57 pm

A rosscojector is that pinched narrow slit tube right? I had a 1/4" hose adapter straight on the propane tank. A rubber tube leading to the copper tube. I had the injector about half way down the throat of the intake and that didn't work. I manually held it about an inch away and that almost worked. Ill get more pics when I'm back home from welding.

This is how it was set up before I left to try it.

Image

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Re: Scrap Queen's first foray into valveless pulse jets

Post by metiz » Mon Nov 02, 2020 4:31 pm

The Rosscojector is that pinched tube, yes. I've linked to it in the other thread. It looks like your copper pipe is kinked. Try bending it in a bigger loop to prevent that. Also use 2 hose clamps to secure the injector and make sure the injector is pointing straight into the intake. See my masterfully crafted paint schematic below.
Attachments
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ScrapQueen
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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Mon Nov 02, 2020 5:04 pm

Thats a very high quality blueprint. I was afraid it was too kinked ive got plenty of tubing left so I'll try it again, thanks! I suppose my injector was that far down the intake after all. I'm scrounging for a big enough piece of sheet steel to roll the exhaust cone on my new engine.

Thanks for all the help too, I don't suppose this place has been as active since its heyday.

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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Tue Nov 03, 2020 9:31 pm

https://i.imgur.com/Xp19VJp.mp4

I made a new injector and it runs! I think!? It roars louder when I jam the torch down it while its running. I feel like it could do more for its size.

Edit: crimped the injector nozzle even tighter and it makes an extremely loud roar for a split second before backfiring. Gonna have make another injector because I feel this one isn't long enough into the intake. Now its getting exciting!

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Re: Scrap Queen's first foray into valveless pulse jets

Post by metiz » Tue Nov 03, 2020 10:39 pm

Is there no sound or is it a problem on my end?
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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Tue Nov 03, 2020 11:29 pm

I dunno, it had sound when I uploaded it. I'll just put it on YouTube. I've gotten rusty at these old types of forums:P

https://youtu.be/Gb6abseTDIg

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Re: Scrap Queen's first foray into valveless pulse jets

Post by metiz » Wed Nov 04, 2020 12:26 am

That's better. It's not running though. You need a lot more gas, like, x3. I don't know if you are wearing any hearing protection but if you're not: for the love of tinnitus, do. When it does lock in, it's going to be the loudest thing you've ever heard.
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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Wed Nov 04, 2020 12:59 am

I can open the gas all the way and it blows out the flame. I don't have a regulator on the tank. I think the rosscojector(?)'s slit was too wide. I pinched one tighter after that video and it makes this phenomenally loud roar for about a half second before backfiring. I think THAT injector wasn't far down the intake enough. I made a third one with about a 1mm slitand its resting about a half to 1/3 way down the intake. I feel like I got a taste of it running for a split second. I feel so close!

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Re: Scrap Queen's first foray into valveless pulse jets

Post by metiz » Wed Nov 04, 2020 1:11 am

If you're using a rosscojector, the injector needs to be positioned farther out instead of in. Pretty close to the flare actually. If the flame blows out, you have your injector positioned incorrectly. To find the sweet-spot, hold the injector in your hand and light it. Hold it in the intake in a position where you hear the motor is growling (like in the vid). Then increase the gas flow. If the growling stops, start repositioning the injector until the growl's back. If the growl increases in intensity, hold it there. once the engine starts running (you'll know) you have the right position.
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Re: Scrap Queen's first foray into valveless pulse jets

Post by ScrapQueen » Wed Nov 04, 2020 1:22 am

Ahhhh further out, I missed that tidbit! Oops. I'll try it again tomorrow after welding is out. Im halfway done with the 4th Pyro joe design just need to roll out a cone for the tail!

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