External valve grid

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GRIM
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Re: External valve grid

Post by GRIM » Wed Nov 26, 2008 12:27 am

Here are some photos of the valve grid fabrication,

The four square tubes were cut off at 45 degrees , then spaced apart with some flat bar, clamped , tacked , and then fully welded, including a “build up” on the valve seat face,

6011 welding rods were used These rods dont leave a pretty bead but do have very good penetration and leave a good pore free deposit that is really quite soft and easy to work ,

I left the tubes that stick out the back in place until I had virtually finished the valve seat faces , they are useful for holding in the vice ,

Only when the valve seats were ready did I cut them off and finish the backside ,

I would not recommend this fabrication technique , I only used it because I wasnt sure the valve grid was going to be succesful , and was reluctant to pay for machining work, for an untested design ,

If I make another one it will be machined from billet aluminium ,

The rest of the engine started out based on Erics calculator , I then
shortened / lengthened , modified the reeds , and fuelling , etc,

Now I have a runner , I am heading back to the original dimensions , that little engine really kicked , even though it wouldnt sustain, (fuelling and reed problems I am certain )

Will post more once I have some firm data ,

G
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Johansson
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Re: External valve grid

Post by Johansson » Wed Nov 26, 2008 12:50 pm

Congratulations! A really nice looking engine. :D

How long has it been run so far, and are there any visible damage done to the reeds?

GRIM
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Re: External valve grid

Post by GRIM » Wed Nov 26, 2008 9:05 pm

Hi Johansson

I have ran this engine about 5 times, allways static , on gasoline for about 30 seconds each run
The reeds are showing damage, see photos ,

I initially thought they were burned, closer Inspection shows they are shattered/fractured, but only on the extreme tips,
You may be able to see in one of the photos the witness mark that the port leaves , I am tempted to cut the reeds back to the minimum maybe only 1mm overlap and give it a go like that,

any thoughts / experiences with this?

G
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Mark
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Re: External valve grid

Post by Mark » Thu Nov 27, 2008 1:56 am

To me that little bit of blue on the reed and examining a photo on page 1 of this post seem to show some overheating of the reed tips. I've blued the edges of some of my reeds, gotten them too hot when leaning out the engine.
If the engine isn't running on its own, forced air or such, sometimes that too can put a strain on the reeds, they don't flex regularly perhaps or that creates conditions not normally seen, like the valves not closing in time and fire or hot gases sneaking past them. Then too, if your engine is really red or yellow hot and is stopped, that heat from the engine can migrate to your valve plate stressing the spring steel, warping the reeds imperceptively or making them brittle.
One other thing comes to mind, a mirror smooth flat surface really helps. I've spent a long time with very fine sandpapers doing figure 8's getting every last flaw or pit out of homemade valve plates.
Oftentimes I've noticed on those really big square pyramid reed banks, you see a valve plate that has a rubber coating for the reeds to strike against, whether the older metal ones or the newer carbon fiber or nylon impregnated ones.

This simple pulsejet of mine, (no welding), the metal is so thick on the 3 inch diameter plumbing pipe that you could come back in 20 minutes and it might still burn your hand to touch it. ha
After it stopped if I ran it a long time, the first thing I would do is whack the head with my pipe wrench to loosen the bell and then unscrew the head from the engine with a very large set of channel lock pliers, get it off before the heat warped the reeds I made for it.
I'm glad to see some valved engines being built, for a long time it seemed nobody was interested. I really liked the proportions of your engine and watching it run. It's as if it's alive almost or processing information at a high rate of speed. Whatever it is, it's something hypnotic.
PS That closeup of your chipped reed reminded me of this piece of art for some reason. Maybe you could bang out some miniature skylines by using this technique with larger reed valves and sell them or have a gallery showing. ha
http://www.flickr.com/photos/gailontheweb/5091531/
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Last edited by Mark on Thu Nov 27, 2008 5:02 pm, edited 1 time in total.
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WebPilot
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Re: External valve grid

Post by WebPilot » Thu Nov 27, 2008 4:20 am

If you continue to decrease the effective vibrating length of each valve, you will
  1. increase its natural frequency, thus reducing the driving frequency ratio thereby allowing the valve to close before +tive pressure ensues in the combustion chamber. (you knew that)
  2. reduce the valve's average tip speed. (you may not know that)
You are running out of length at the free end, so you may want to think again about a cover clamp plate at the fixed end.

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PyroJoe
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Re: External valve grid

Post by PyroJoe » Mon Dec 01, 2008 12:51 am

Grim,
Have you tried putting a shield of some type between the core of the CC and the valves? If some of the hottest gas core finds it's way back to the valves it could fast temper the valves with the next cold air surge. Basically tempering the edge akin to glass. Have you tried bending the cooked edge with a pair of needle nose pliers? If so does the edge snap like a twig or bends nicely without cracking. Great build.
Joe

Viv
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Re: External valve grid

Post by Viv » Mon Dec 01, 2008 1:11 am

Hi Joe

Interesting peace of lateral thinking and one that I actually know about but had not applied to the problem, glass hard is some thing I learned about in tool sharpening as a professional wood turner (another life now) interesting that you applied it and could be a part of the problem, can I add another surface hardening method to your thinking called peening, could also add to the edge problem.

Viv

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"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke

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GRIM
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Re: External valve grid

Post by GRIM » Mon Dec 01, 2008 2:10 am

Hi Joe
Good feedback ,
I tried the needle nose pliers test , the “burned end” bends about 80 degrees then breaks off,
However It doesnt “snap” as one would expect if it were hardened and not tempered ,
I tried the same test on the Clamped end , same deal , about 80 degrees ,
Also tried some virgin shim , from the same stock , same deal ,

I tried some 10 thou , shim That I obtained recently, that will actually bend 90 degrees without breaking , if I try to bend it back it breaks off ,

In light of these tests I am somewhat suspicious of the 8 thou shim ,
It measures 0,0085” and it doesnt have the same nice even dark blue temper that the 10 thou has, It is slightly streaky , and I suspect that it may be Reject material ,

Time to try some 10 thou reeds I think , In actual fact they are allready made , fitted and awaiting an oportunity , dfr 0.5 , one step at a time ,

Thanks for posting ,

G

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Re: External valve grid

Post by PyroJoe » Mon Dec 01, 2008 3:05 pm

Not sure what valve material should be, but that material sounds a little brittle or to high in carbon content. Bet this stuff is cold rolled and therefore somewhat hardened. One thing you may want to try with the 8 thou, is to take a valve sized piece and heat it up to slightly red heat and immediately bury it in a bowl of dry ashes letting it sit in there for hours, slowly cooling. After cooled see if it will then bend near 170 to 180 (with about 2mm radius on the bend) and back without failing. If she still fails at 80 deg. then she probably has to much carbon.


Also check the grain, see if the grain is oriented parallel to the bend or perpendicular. This is easy for some material, just bend it over a tight radius and watch how the tensile side starts to fail. One direction it should fail easily and greyish cracks start appearing parallel to the bend. May need a magnifying lens for this thin stuff. It appears in the picture that the grain is oriented correctly in the damaged valve.

Joe

GRIM
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Re: External valve grid

Post by GRIM » Mon Dec 01, 2008 9:30 pm

I would like to mention at this point some of my ¨thinking¨ behind this concept,

Many years ago, I had a motorcycle that had reed valves; these were steel reeds installed in aluminum valve blocks located almost immediately after the carburetors,

The valve grid and reeds I have used in the G59 are not unlike the Yamaha setup,

To come to the point, these valves had a useful life of quite literally, YEARS! Considering daily to and from work use,

Now it has to be said that in the case of the motorcycle engine, the reeds are a kind of secondary valve, the piston port arrangement ensures that the reeds are never subjected to the combustion event, thus never achieve even ¨warm ¨ temperatures, they are only there to allow the fuel air to enter and, avoid that it comes out again , a check valve really ,

However, some simple math tells me that at 9000 rpm, the Driving frequency acting upon the reeds would have been 150Hz

The racing version redlined at 13500 rpm 0r 225 Hz

This style of engine is still being built in 2008 for competition use, and as far as I am aware, the reed valve is NOT one of the major ISSUES with regards to reliability,

True, they use carbon composites these days, but steel was common up to a few years ago,

The Timing of the valves would (I think) be quite different in a two stroke internal combustion engine “open less time, closed for more time per cycle” and they are likely subjected to much less violent shockwaves,

But The BIGGIE for pulse combustor use, seems to be the temperature, and How to minimize the effects of this on the valves,
Maybe what is needed is a second valve, prior to the reeds, not necessarily mechanical, not necessarily perfect, maybe an Inertiance type valve,

A Hybrid,

On the other hand it could easily turn into a OCNIGH, (over complicated, noisy, inefficient, garage heater), I have allready got a couple of them,

Any thoughts?

G

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Re: External valve grid

Post by PyroJoe » Mon Dec 01, 2008 10:47 pm

If my general thinking is correct, the stroke of the two stroke engine is compressing something like 1/4 of the crankcase, (of course a racing engine may be different) which should be producing compression of about 1/4 of an atmosphere. If so, those valves should be seeing something like 4-5 PSI max. It has been posted somewhere in the valveless section that many PJ should be capable of around 12 psi.

Also the piston sees the most of the hottest gas, after the gas has expanded and done its work. The exhaust gas is probably a lesser fraction as hot as core gas in a PJ.

Hope this helps some.
Joe

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Re: External valve grid

Post by Ghrey » Tue Dec 02, 2008 8:08 am

I would be inclined to agree with Viv, only we always called it work hardening, either way it can cause the material to become brittle and fail.

One other thought I had was an extreme case of valve over flexing ( lash if you will... ) due to too thin a stock...


This is the second thread that has gotten me thinking about the old "Lancer" .: download/file.php?id=10995&mode=view :.
may be I should pick it up again....
In the process of moving, from the glorified phone booth we had to the house we have.

No real time to work on jets, more space, no time.

Life still complicated.

GRIM
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Re: External valve grid

Post by GRIM » Tue Dec 09, 2008 1:37 am

Here is a short vid of my EVG 043 ,

Thats Eckstein Valve Glider , or External Valve Grid , whatever works for you , :D

This one has the valves tuned to dfr 0.43 ,

The photo is the valves after two, approx 1 min runs, there is NO fracture damage as was observed in previous runs with other ratios , In fact the valves are in perfect condition,

The gunk on the cover plates is a paste I use to seal everything up ,

I am very happy with this,

Thrust testing up next , I dont expect this engine to be incredibly powerful , there is not sufficient valve area , but thats just an engineering problem , the important thing is that the valves survive (very well )

By the way the duct was built to Eric Becks calculator , thank you Eric , very cool program

G
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Re: External valve grid

Post by Viv » Tue Dec 09, 2008 2:01 am

Hi Grim

Nothing wrong with that motor ;-) sounds nice and clean, I love the fact that you have built this using maths and are getting such good results

Viv
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WebPilot
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Re: External valve grid

Post by WebPilot » Tue Dec 09, 2008 4:45 am

G,

Am I dreaming? I keep pinching myself, and yes, I'm awake. This is infriggin'credible! :shock:
Here is a short vid of my EVG 043, that's Eckstein Valve Glider , or External Valve Grid , whatever works for you , :D
That's clever. I like it.

But then you are clever. You have demonstrated your mastery of engine building and have been a most excellent student of my valve glide theory. I give you an A+.

Thanks for the belated birthday present.

PS ... we've still got to make one fly.
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