Valve Intake Area

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cbromano
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Valve Intake Area

Post by cbromano » Thu Dec 25, 2003 8:08 am

I'm trying to build a pulsejet and I have a few questions-
How big of a valve area do I need to keep my jet going?
I am using more or less Chris Beck's Calculator based on a 25 lbs thrust engine-
The tail pipe is galvanized 3-inch pipe w/ a 2.82 inner diameter
(YES I do know the zinc can kill me but finding stainless steel pipe in my price range has been fruitless)
I have access to CNC machines so I am trying my hand at making trapezoid shaped openings.
Size has become the issue because I have little knowledge of how wide of gaps the spring steel can span and how much to let the valves move.
Any suggestions?

Also I am very interested in the research Schmidt did with the V-1 does anyone have any of his papers in English? All I can find locally is a collection of Reynst’s papers on Pulsating Combustion.

Thanks
CB Romano

PS- Does anyone know the PSI of a propane tank?
I don't wish to know everything.
I just wish not to be ignorant.

Mark
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Post by Mark » Thu Dec 25, 2003 11:51 am

If you are running a pulsejet outdoors, I don't think you would ever have to worry about zinc or galvanized pipe in the least.
Mark

Viv
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Post by Viv » Thu Dec 25, 2003 12:44 pm

Merry Christmas

The Argus zip is a bunch of drawings and the Schmidt Gosslau zip is a very good set of extracts originally provided by Andrew.

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

Viv's blog

Monsieur le commentaire

Mark
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Post by Mark » Thu Dec 25, 2003 6:04 pm

Mark wrote:If you are running a pulsejet outdoors, I don't think you would ever have to worry about zinc or galvanized pipe in the least.
Mark
Often, most hardware stores offer stainless steel, galvanized pipe, and something called black iron which is the cheapest of the three. It rusts easily though but who cares if you are going to use it for prototyping.
Mark

Eric
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Post by Eric » Mon Jan 05, 2004 4:59 am

It is Eric Beck's calculator! ;)

If you have access to CNC equipment then you shouldnt have a problem getting the wedge shaped intakes accurate. I am assuming that you are going to use the "high efficiency" petal valve system, for an engine producing 25 pounds thrust I probably would of picked a valve grid system because it might be a little more simple. The only down fall of such a valve grid would mean you would probably have to weld the aluminum valve plates to create the shape.

If you are going for the improved petal valve system then try to pack as much valve area into the valve plate as possible. Having too much valve area is not as big of a problem as having too little, if you have too much you could always make the valve plate a little more restrictive. The span that the spring steel must cover could become a problem, you will probably have to use at least 12 valve petals AT LEAST... probably more along the lines of 14. This is one of the reasons why a circular array system becomes more difficult to scale up.

Make sure to make everything fit nice and snug so that there are no leaks which keep the engine from running, and make sure the fuel system is well made, these are probably the main things in making sure the engine runs. I am beginning to think the valves dont really matter much since I was able to run my little dynajet on a valve that only had 9 of its 10 petals.. then again when that thing runs orange hot its pretty hard to stop short of yanking off the fuel line ;)

Good luck with everything, email me if you have any questions about the calculator or design stuff...

Eric

Mark
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Post by Mark » Mon Jan 05, 2004 6:03 am

Eric wrote:It is Eric Beck's calculator! ;)

If you have access to CNC equipment then you shouldnt have a problem getting the wedge shaped intakes accurate. I am assuming that you are going to use the "high efficiency" petal valve system, for an engine producing 25 pounds thrust I probably would of picked a valve grid system because it might be a little more simple. The only down fall of such a valve grid would mean you would probably have to weld the aluminum valve plates to create the shape.

If you are going for the improved petal valve system then try to pack as much valve area into the valve plate as possible. Having too much valve area is not as big of a problem as having too little, if you have too much you could always make the valve plate a little more restrictive. The span that the spring steel must cover could become a problem, you will probably have to use at least 12 valve petals AT LEAST... probably more along the lines of 14. This is one of the reasons why a circular array system becomes more difficult to scale up.

Make sure to make everything fit nice and snug so that there are no leaks which keep the engine from running, and make sure the fuel system is well made, these are probably the main things in making sure the engine runs. I am beginning to think the valves dont really matter much since I was able to run my little dynajet on a valve that only had 9 of its 10 petals.. then again when that thing runs orange hot its pretty hard to stop short of yanking off the fuel line ;)

Good luck with everything, email me if you have any questions about the calculator or design stuff...

Eric
Here's these V-petal valves. I bought a set of them but never have gotten around to using these store-bought designs. Each V-valve bank is held on the plate with just two 1/4 20 common screws. I bought an almost new 6 pack of these for much less on ebay a long time ago, but never had a big enough pipe to fit them in, they are a little over 4 inches wide. I suppose I could have angled them on the sides of the pipe and sanded them till they curved flush with the inside of the hypothetical pipe.
Anyway maybe someone on this forum could come up with a clever use for this style of reed. I thought about using just one and squashing the front end of a pipe to widen it to fit inside and cut out a plate of aluminum to mount the reeds to the pipe. The jet might look like some strange gulper sea creature. Or maybe a square or triangular piece of odd pipe might do.
http://cgi.aol.ebay.com/ebaymotors/ws/e ... 2451829866

Eric, did you start the Dynajet with 9 petals as a lark or did one fly out the end and it just kept running? Have you tried 8 petals yet, just to push the envelope?
Mark

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Post by Eric » Tue Jan 06, 2004 1:08 am

I started the engine with all the petals, one was pretty damaged and I knew it was not going to last. After the engine got orange the damaged petal flew out the back at about 600 mph! It kept on running. I was trying to get it to run until the valve failed completely but I never got that far, about a minute after the petal busted off I got a stream of sparks out the tailpipe that rivaled many fireworks spark fountians, yet it was still running. I quick ran over and pulled off the fuel line. The rest of the valve was more or less ok, the retainer didnt fair so well though. If i can figure out how to post this picture you can see for yourself.

Eric
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Mark
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Post by Mark » Tue Jan 06, 2004 1:44 am

Eric wrote:I started the engine with all the petals, one was pretty damaged and I knew it was not going to last. After the engine got orange the damaged petal flew out the back at about 600 mph! It kept on running. I was trying to get it to run until the valve failed completely but I never got that far, about a minute after the petal busted off I got a stream of sparks out the tailpipe that rivaled many fireworks spark fountians, yet it was still running. I quick ran over and pulled off the fuel line. The rest of the valve was more or less ok, the retainer didnt fair so well though. If i can figure out how to post this picture you can see for yourself.

Eric
That's an interesting story, looks like a melt-o-rama on the valve retainer. I'd have liked to seen the sparks fly. There's nothing like actual research. It reminds me of Larry's spark-o-rama by inserting tubing up inside a running Dynajet from the tail end, seeing how important cooling is inside the blast furnace of pulsating combustion. It's something to keep in mind when designing tubes within a tube.
Mark

Dmitry Petrov
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Sparks fly

Post by Dmitry Petrov » Fri Jan 09, 2004 5:05 pm

Hi all !


Sparks fly from a petal, but the engine continued to work. Even serious damages of an environment (a skin of combustion chamber, a shirt of the engine) do not stop his work. On old hearings (old narrator) on engine Argus by the end of flight was only 50 % of valves and it continued to work...


WBR
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my own engine
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Mark
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Re: Sparks fly

Post by Mark » Fri Jan 09, 2004 8:36 pm

Dmitry Petrov wrote:Hi all !


Sparks fly from a petal, but the engine continued to work. Even serious damages of an environment (a skin of combustion chamber, a shirt of the engine) do not stop his work. On old hearings (old narrator) on engine Argus by the end of flight was only 50 % of valves and it continued to work...


WBR
That's a good piece of information Dmitry. It is said a high speed pulsejet, perhaps going 450 mph, becomes a poorly running ramjet, this idea is presented in Foa's book, "Elements of Flight Propulsion." The valves at this speed don't get the opportunity to spring completely closed. Stick your hand out the window of your car at 75 mpg and feel the pressure, then imagine 6.5 or so times as fast.
And too let's not forget Chris's valveless trianglodyne. It created another breathing port where the spark plug mount separated and allowed further breathing from the side of the combustion chamber. Maybe it wanted to become/evolve into a Lockwood/Logan hybrid.
It's funny how a pulsejet can continue on with seemingly mortal wounds and keep fighting. And on the other hand, conjuring life out of a well-planned tube might just look the other way and be disinterested in what you think should happen. There's nothing like experimenting to gain insight. It took me a long time to figure out what was going on with my jumbo jam jar tank, why it just stopped out of nowhere.
I think it runs for 5 minutes plus now because I have lessened the combustion/heat process and it can tollerate long runs because it doesn't glow red hot and flame out with fuel left in the tank. I have reduced the amount of air it can breathe, combustion is slower with a skinnier snorkel, yet lasting, an even trade with fuel evaporating and pulsating combustion. The 2.5 gallon tank with snorkel makes occasional staccato popping sounds in succession, mixed inbetween the lower energy steady in/out jam jarring combustion, as if it were chomping at the bit, yet confined to live at the cooler combustion rate.
With five minute runs you can wander into your house, chit chat with company and then go back outside and continue watching the stop watch I have timing it.
But such a device is of little practical use, unless you find noise and exhaust flames entertaining. Oh, it might be good for inflating a small hot air balloon or baking/broiling some Gulf of Mexico fish or shrimp for five minutes against the stainless steel.
Mark

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