Improved Tundra-Jet Valve Array

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Mike Kirney
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Improved Tundra-Jet Valve Array

Post by Mike Kirney » Mon Oct 06, 2003 5:18 pm

With the temperatures getting lower, pulsejet season has finally arrived here in the scenic Bonnechere Valley. I just finished doing the 'first draft' computer-generated layouts of the Tundra-Jet Losenge Valve system. These JPEGs are full-scale so you can print them off and make your own, although be warned, the page with the nine 'losenges' came out a little wierd. The centre-punching marks don't line up with the ones on the valveplate and the reeds are all a couple of millimetres oversize (don't ask me why). With an exhaust outlet of 12 cm diameter (113 cm2), I'm hoping the total 103.5 cm2 of inlet area will be enough. I'm planning on holding the losenge-shaped reeds to the valveplate with 1/8" pop-rivets and maybe a little JB Weld here and there. The hole in the centre of the valveplate is to accomodate the old welding torch I use as fuel supply.
Attachments
valveplate1.jpg
I hope the holes are not too close together.
(30.37 KiB) Downloaded 1003 times
losengesheet.jpg
Eight losenges, with one extra just in case.
(19.85 KiB) Downloaded 1005 times

Mike Kirney
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Opinions Please

Post by Mike Kirney » Mon Oct 06, 2003 5:24 pm

Each losenge comprises two individual reeds. The reeds are about 3cm long and 2 cm wide. Do you suppose these will be too big? I think I'm going to build this thing this afternoon, so I hope I get some replies before its too late!

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Re: Opinions Please

Post by larry cottrill » Tue Oct 07, 2003 12:26 am

Mike -

I don't see how they could be too close together. The valve ports on the Dynajet are a small fraction of an inch apart. The main thing is to make sure the total area is what you think is just right [and, of course, that the reeds open sufficiently to get the air in freely]. Big is good, I think, because bigger means more opening [and closing] force for the same pressure difference. I'm not understanding how you intend to limit the travel on opening, and for that matter, keep sharp bends from occurring.

L Cottrill
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Mike Kirney
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Hadn't Really Thought About It

Post by Mike Kirney » Tue Oct 07, 2003 12:51 am

"I'm not understanding how you intend to limit the travel on opening, and for that matter, keep sharp bends from occurring."

Hadn't really thought of either of those two things. I still have about 35" of stainless shim left and I just got a 4 x 8 of 16 ga. mild steel, so I'm just gonna work things out as they happen. If anything, I was expecting the losenges just to flutter away and take care of themselves. I was just going to rivet them in place with no bends or anything.

Pieter van Boven
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Re: Opinions Please

Post by Pieter van Boven » Tue Oct 07, 2003 3:49 pm

Larry Cottrill wrote:Mike -

I don't see how they could be too close together. The valve ports on the Dynajet are a small fraction of an inch apart. The main thing is to make sure the total area is what you think is just right [and, of course, that the reeds open sufficiently to get the air in freely]. Big is good, I think, because bigger means more opening [and closing] force for the same pressure difference. I'm not understanding how you intend to limit the travel on opening, and for that matter, keep sharp bends from occurring.

L Cottrill
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Big isn't good I think because the reeds will be blown out trough the valveholes. For example: The pulse-jet 90 design is also used for bigger engines (just like the one that is for sale on the "old" forum). I also made a bigger valveplate with a diameter of 120mm (it's on my site) but was adviced not to use it because of the wide valvehole surface. I should have made it with 13 valves. If I had to make my PJ90 again, I would make it with 13 holes also because I think this would give much longer valve-life.

Pieter.

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Post by Pieter van Boven » Tue Oct 07, 2003 3:52 pm

Here you can see my 120mm valveplate. Lot of work for nothing..

Pieter.
Attachments
onderdelen.jpg
onderdelen.jpg (6.29 KiB) Viewed 10323 times

Mike Kirney
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Have You Tried It Anyway, Pieter?

Post by Mike Kirney » Tue Oct 07, 2003 11:53 pm

I hope you've tried using it at least once. You never know, it might work just fine.

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Post by Pieter van Boven » Wed Oct 08, 2003 3:44 pm

No I didn't. It's the first pulsejetpart I made and it was ment for a big engine. After some reading on the forum and some advice of several visitors I thought it would be wise to start a bit smaller and with a proven design.
The other parts aren't used either. The dynajet valvehead is complete with retainer and combustion chamber/pipe but I still didn't put it together. I don't like the metering jet (very small parts) and don't want to run it on propane. I should learn to finnish things....

Pieter.

Mike Kirney
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You Should Try One Out

Post by Mike Kirney » Wed Oct 08, 2003 10:26 pm

Your pieces look very well-made. Its too bad you haven't tried any of them. Is propane very expensive in the Netherlands?

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Re: You Should Try One Out

Post by Pieter van Boven » Thu Oct 09, 2003 4:02 pm

Mike Kirney wrote:Your pieces look very well-made. Its too bad you haven't tried any of them. Is propane very expensive in the Netherlands?
No, it's the cheapest fuel you can drive your car with over here....I just don't like to use it for a pulsejet.

Pieter.

Ivar
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Post by Ivar » Sat Oct 11, 2003 11:01 am

Too little intake area versus entire valvplate area \ ratio.

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Post by Pieter van Boven » Sat Oct 11, 2003 11:46 am

I don't think so Ivar. The retainer can be made with a small diameter if you are using thicker valves. It will work but with 13 holes, valvelife would be higher. Ofcourse a V-grid valve assembly would be better for combustionchamber diameters above 120mm.

Pieter.

Mike Kirney
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Valve Area

Post by Mike Kirney » Sat Oct 11, 2003 1:51 pm

I think he might have been talking about my jet, Pieter. Ivar, I'm not sure if I have provided enough valve area either, but if it doesn't work I have plenty of room to make more valveholes. The important ratio is effective valve area to exhaust area. Right now the aggregate total area of all the valveholes is 103.5 cm2, and the tailpipe has an area of 113 cm2. This equates to an intake/exhaust area ratio of 0.916:1 . I checked some other jets and many of them are very near 1:1 and some are as high as 1.9:1 .

Ivar
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Post by Ivar » Sat Oct 11, 2003 4:17 pm

It CAN be used but think of what diameter the jet will be where the plat is located.
Wear will NOT be decreased as in V grid the valves are not hit "head on" but like 45 degrees or so.
Asymmetric location of valves will give different wear-out time too, and make the fluid flow much more decentralised.

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arabian sneaker effect revisited.

Post by Troy R. Legner » Fri Oct 17, 2003 7:39 pm

Gentlemen,
There was once a posting called the Arabian sneaker effect. This is what happens to valves without a retainer that will limit the travel and contour of the warping effect of the heat. I have had this happen to one of my designs. When I took it apart the valves were warped up in a curl like an Arabian sneaker. Ivar commented on the angle the valve sits in the grid relative to the axis. Valves at angles are less likely to experience this problem as those that sit flat on the grid plate, 90 to the axis. I would think that a proper retainer would prevent these types of problems. You might try clamping a reed flat down and lifting the leading edge to get an idea of the correct shape to make the retainer to match the curvature of the opened reed.
Troy L.

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