external valved engine

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Jim Berquist
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external valved engine

Post by Jim Berquist » Sun Apr 29, 2007 8:23 pm

I came across this today. Anyone know who made this?

I like the idea. As you can see someone place there hand behind the engine, the thrust must be rather low. I like the idea of the valves being out of the C.C. and away from the heat. With the three sets of peddles, the work load is being shared so to speak. If the valves was place forward unlike they are would that assist breathing in flight?

Jim

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dynajetjerry
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External valve

Post by dynajetjerry » Thu May 03, 2007 2:30 pm

Jim,

The p-j arrangement to which you referred does, indeed lengthen valve life but at Curtis Dyna-Fog, Ltd, in 1953-54, we came up with a similar system (at the time, the company was Curtis Automotive Devices.) We separated the small chamber holding the valve from the much larger combustion chamber. They were connected by an elbow whose I. D. was slightly smalller than that of the 4 foot long tailpipe.

This system kept the valve cool and, with the long tailpipe, greatly reduced impact damage to the reeds. The result was labelled "Dyna-Fog, Jr." and was the second DFG, Jr. The first was devised by Jerry Nolin and me in 1952 and was similar the the original DFG, though smaller, and was kept cool by being immersed in a water bath. (I still have the latter in my backyard shed, along with the prototype DFG, production S. N. 101, and 121.)

The air-cooled Junior is still produced, having been discussed in this Forum previously. Of course, today's DFG, Jr. is much superior to our original, having benefitted from 40 years of "tweaking" the design. In my experience, the most significant change has been been the ability to operate on gasoline that has a much lower vapor pressure than the gas of 1954. I have a 1956 DFG, Jr. but I can't get it to function unless I use the older type of fuel.

Jerry
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Jim Berquist
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Post by Jim Berquist » Thu May 03, 2007 2:53 pm

Dynajetjerry:

The back grounds of some of the people in this forum never cease to amaze me. It's people like you that make up the heart of the forume.

I really would like to know more about this one. I need to chase down some links and check it outl

Thank you Jim
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dynajetjerry
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external valve pulsejet

Post by dynajetjerry » Thu May 03, 2007 9:08 pm

Jim,

Whatcha wanta know about the DFG, Jr. or the original?

Jerry
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Jim Berquist
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DFG jr or original

Post by Jim Berquist » Fri May 04, 2007 12:30 am

I know nothing. That's why I need to learn. I am on this forum to learn and learn I will. Thank you to the people that will teach me! People like You!

All I know as of so far is External Valves , Less Heat on the Valves, Less Compression exerted on Valve, Less Damage Due to Same, Valves could be set as to except some ram air. I have not as of yet Googled It . I will do it now!


Jim
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larry cottrill
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Engine Sticking Its Neck Out

Post by larry cottrill » Fri May 04, 2007 2:30 pm

Jerry -

Did you/they ever try the valves at the front of a short CONICAL front chamber? That seems (to me) like it would enhance getting the air-fuel mix back into the combustion chamber proper (nozzling), and it would slow down the portion of the explosion mass that gets kicked back toward the valves (some diffusion effect, plus the shear and turbulence you get with a "neck" pipe between cylindrical chambers). Just a thought.

I have seen a plan (not necessarily to scale) of that two-chambered Dyna-Fog arrangement and wondered how it could help. But, obviously, it does. What are the downside issues (if any) to that design? Does it slow down the engine cycling from what it would otherwise be (i.e. with the same overall length, but without the "neck")?

L Cottrill

dynajetjerry
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External valve p-j

Post by dynajetjerry » Fri May 04, 2007 6:59 pm

Larry,

The downsides to our 2-chamber p-j is important, mainly, to its use for thrust and/or in aeromodelling.

Obviously, weight is much, much greater than traditional designs and thrust is less; never having tried to measure the output, I don't know how this design compares with the similar-sized Tigerjets. (I am referring to tailpipe cross-sections, not length or weight or power or efficiencies.)

For our application in the DFG, Jr., the 2 chambers prevented heat from reaching the reed valve and valve head assembly. In fact, as I probably mentioned before, my early endurance tests on the prototype DFG, Jr. resulted in its valve head icing up and stoppage of the engine. I was running it on a cool, damp day and the vaporizing of the gasoline cooled the intake to well below freezing. Another consequence of the cool intake was condensation of moisture on the valve, leading to rust spots on those made of the blued spring steel that are also used on most airplane p-js. Our cure was to adopt a spring-temper stainless material.

I don't think cycling frequency was much affected by this design, being about the same as a standard, small p-j of a similar length (slightly less than 5 feet,) about 125 cps.

We did make a crude version of this arrangement for an original DFG engine, also incorporating a wedge valve design to permit casting of the valve head. It turned out to be a pretty worthless exercise and nothing came of it.

Jerry
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dynajetjerry
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External valve p-j

Post by dynajetjerry » Fri May 04, 2007 7:12 pm

Larry,

I forgot to address your question about a conical valve head chamber. The front of the main combustion chamber is conical, as is the rear, where it merges with the tailpipe. But the exact shape of the separate chamber appeared to be rather unimportant. We varied volumes and downstream shapes of the chamber, also making use of valve retainers that had various downstream shapes and thicknesses. In fact, the the engineer in charge (Paul A. Frank, an alumnus of Aeromarine,) opined that our keeping the clearance between the retainer and the inside surface of the chamber served to "wash" away any tendency for fuel to accumulate. Thus, volume seemed to be of little importance but the cross-section and effective length of the connector between the C-C and valve head chamber was.

Jerry
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Jim Berquist
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dyna jet

Post by Jim Berquist » Fri May 04, 2007 7:52 pm

All I found so fare is that the company that made the Dyna Jet now makes bug foggers!

Do you have any more? Out lines, Plans, Photo's, else? Did you find a formula related to the valved intake manufolds and the tail, CC, that would fire up and run? What kind of thrust was available?

I wonder it the basic shape and CC of the chines, with out intake would lend it's self as a snorkled valved breather?

Jim
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leo
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dyna jet fogger

Post by leo » Fri May 04, 2007 10:31 pm

Jerry is the noise off these Dyna jet foggers the same as from a Dyna jet pulsejet, or is it much less.
Is the noise a real problem for users or is it acceptable.
I ask you because I think you have a lot of experience with them.
Would it be a big improvement to reduce the noise much?.

dynajetjerry
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external valved engine

Post by dynajetjerry » Sat May 05, 2007 4:06 pm

Jim,
In the p-j design we are discussing, thrust was not a factor so we did not try to measure it. I would guess it was pretty near to 1 lb., based on its exhaust pipe and the performance of small, conventional p-js.
I have some photos and drawings but have not been able to post any of them on the web. And, so far as I can remember, there were rather few true calculations made by Aeromarine personel during development of any of their products. Most designs were the result of "trial and error" work or "cut and try" to come up with devices that were suitable for the proposed applications. In those days before computers, none of us even required a slide rule!

Leo,
Noise levels of these long p-js are much less than the Dyna-Jet, mostly because of the lower cycling frequencies and less sharpness of their explosions. While somewhat disturbing to a few people, the noise levels of our insecticidal generators, though substantial, were not annoying to most of us because of the lower frequencies.
Reducing noise is certainly possible but not at all practical. During our development of pulse-jet based smoke-screen generators for the Navy and Army in 1951-52, we untilized housings that completely enclosed the p-js and that acted as mufflers. You can go to the Web and type in "M157A2 smoke generator" to call up today's copy of our 1952 design. You will see the discharge end of the generator, on a motorized carrier, as equipped for Army use.
Whereas our Dyna-Fog generator was unmuffled and weighed about 110 lbs., dry, our E19R1 (predecessor to the M157A2,) weighed about 150 lbs. Fabrication costs were approximately 3-4 times that for the DFG, though the smoke generator could produce fog from 25% more oil than the DFG.
(Part of the increased costs were due to our need to conform to military standards.)
Jerry
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Dj Nafets
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No advanteges

Post by Dj Nafets » Thu May 10, 2007 3:54 pm

I don´t see any advanteges in this design of a engine. In my opinion there are nearly only disadvanteges.

- The fuel/air mix isn´t good, as you can see at the yellow flame
- The mass is even higher than with traditional design
- The engine ist much complexer then a normal one

If you want to increase the lifetime of the valves, there are much more effective ways.
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Jim Berquist
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external valved engine

Post by Jim Berquist » Thu May 10, 2007 4:36 pm

DJ

Valve life is the akilies heal of the valved engine. People have tried various fixes. They have coated them with neoprene rubber. Tried soft valve seats. Placed baffles between the valves and the C.C... They have all but exhausted the materials list for valves.

Give me 20 hours!

What are the other ways?

Jim
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Dj Nafets
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Post by Dj Nafets » Thu May 10, 2007 6:03 pm

Ok, you are now checking seriously my english language knowlage ;) ;)

There ar two problems that are limiting the valvelife:

- the thermal stress
- the machanical stress

The first problem is nearly completely disolved by the arangement of fuel nozzles an attached flameholders.

So, there is only the mechanical stress wich consists of two problems:

- the bending
- the impact force

Bending is not that huge problem because the materials that are used can resist it very good.

The major problem is the impact force. It can be reduced, but not be eliminated with valved design. Ways to reduce the force are:

- soften the valve seats
- soften the valves
- reducing the valve velocity
- reducing the valve way

As you can see in the pivture below, I tryed a layer of 1mm Viton on my valveplates. But it isn´t reliable enough. A few days ago, I got a rubber coated valve.
The effort to coat these parts is to high in my eyes.
Increasing the valve area, reduce the velocity of the valves by decreasing the valve way that is necessary.

And that is exactly what has be done at the pulsejet in the video.

It has nothing to do with external valves and the temperature of them. I´m going to follow that way using "normal" design in the future. But it will take time.
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ventilplattemitgummi.jpg
Viton coated valveplate
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Jim Berquist
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external valved engine

Post by Jim Berquist » Thu May 10, 2007 6:47 pm

I wish I could speak deutchlander as well as your English.

Cool . I agree larger valve area could stem off the problems to a point. What kind of life do you expect from the coated valves? There are better matiarials out there then in the past. As we both stated, soft seats would help. A larger valve face, with more serface area would help as well. Some new carbon fiber materials hold promis and are used for other outboard motors and motorcycles. They just are not ready for the beating required within the P.J.

Soo! Your Idea is to inlarge the area and limit the motion, travel of the valve.

Tell me more!

Jim
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