Designing a 200lb thrust engine, anything majorly wrong?

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TonyG
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Designing a 200lb thrust engine, anything majorly wrong?

Post by TonyG » Thu Dec 04, 2003 1:12 am

I am working on my first pulsejet engine, and it seems I decided to start big. I am hoping to produce around 200lb of thrust, and yes it will be mounted on a gokart. I am doing this as my welding project at my highschool, and have access to several mig welders, stick welders, a tig welder, plasma torch, brake shear and a few other tools. I have already purchased the stainless steel, type 304, and have 3 peices of the following dimesions, 2 24"x60" and a 32"x60" sheet, all 20 guage.
I am basing the dimensions on Eric Beck's pulsejet generator program, and formulas from the "Inside the Pulsejet" papers.
Total length: 81.25 inches
Exhaust Tube Lenght: 48.75 inches Diameter: 8 inches
Combustion Chamber: 16.25 inches Diameter: 11.625 inches
Reducer: 16.25 inches
Valve Flow Area: 24.299 square inches
Thrust, figured at 4.4lb thrust/square inch: 217lb thrust
Exhaust Velocity: approx: 440ft/sec or 300miles/hour
Engine Frequency: 98.73Hz

The valve flow area is what I am most unsure about, along with the exact valve setup, the number just seems to small to me, but maybe not. I am using a valve grid setup, just unsure about the best angle to use when building the valve plates and what not.
If you have any advice, please let me know.
Also, I am planning on making the valve plates out of aluminum, but the thought of titanium has crossed my mind, lightweight and strong, but would it seal correctly with both the spring steel valves and the titanium valve plates being hard materials?

Thank you,
Tony

Mark
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Re: Designing a 200lb thrust engine, anything majorly wrong?

Post by Mark » Thu Dec 04, 2003 3:59 am

TonyG wrote:I am working on my first pulsejet engine, and it seems I decided to start big. I am hoping to produce around 200lb of thrust, and yes it will be mounted on a gokart. I am doing this as my welding project at my highschool, and have access to several mig welders, stick welders, a tig welder, plasma torch, brake shear and a few other tools. I have already purchased the stainless steel, type 304, and have 3 peices of the following dimesions, 2 24"x60" and a 32"x60" sheet, all 20 guage.
I am basing the dimensions on Eric Beck's pulsejet generator program, and formulas from the "Inside the Pulsejet" papers.
Total length: 81.25 inches
Exhaust Tube Lenght: 48.75 inches Diameter: 8 inches
Combustion Chamber: 16.25 inches Diameter: 11.625 inches
Reducer: 16.25 inches
Valve Flow Area: 24.299 square inches
Thrust, figured at 4.4lb thrust/square inch: 217lb thrust
Exhaust Velocity: approx: 440ft/sec or 300miles/hour
Engine Frequency: 98.73Hz

The valve flow area is what I am most unsure about, along with the exact valve setup, the number just seems to small to me, but maybe not. I am using a valve grid setup, just unsure about the best angle to use when building the valve plates and what not.
If you have any advice, please let me know.
Also, I am planning on making the valve plates out of aluminum, but the thought of titanium has crossed my mind, lightweight and strong, but would it seal correctly with both the spring steel valves and the titanium valve plates being hard materials?

Thank you,
Tony
That's ambitious. Pulsejets are the simplest engines in the world. You should have no problem banging one out. You will be surprised how everything falls in your lap. But then again you may not be surprised. You may wish you selected something smaller to practice on first.
But small pulsejets can be harder than big pulsejets. Most of the people on this forum are probably amused by your ambition. When do you have to complete your project or what time frame are you planning to test fire this baby?
Mark

TonyG
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Post by TonyG » Thu Dec 04, 2003 4:53 am

I am hoping to have it up and running by the end of January if at all possible. I will have about an hour everyday to work on it while at school, so hopefully I will be able to finish it. I am planning on entering it in the TSA contest, in one of the metal fabrication categories, and am pretty much guarenteed to go to state contest with it, as the school I am attending is one of the few in the area to have a metal shop. I also plan on getting a website setup, if I can find the time, to show my progress with the engine and post some info on some of my previous projects.

Mark
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Post by Mark » Thu Dec 04, 2003 5:03 am

TonyG wrote:I am hoping to have it up and running by the end of January if at all possible. I will have about an hour everyday to work on it while at school, so hopefully I will be able to finish it. I am planning on entering it in the TSA contest, in one of the metal fabrication categories, and am pretty much guarenteed to go to state contest with it, as the school I am attending is one of the few in the area to have a metal shop. I also plan on getting a website setup, if I can find the time, to show my progress with the engine and post some info on some of my previous projects.
How did you become interested in pulsejets? 200 pounds of thrust is a lot of noise and energy. Have you ever seen a pulsejet running? It can be done, but I would design in some overkill in strength and what are you planning to use for fuel? There are so many little things to know that would be helpful. Wear eye and ear protection when you toy with starting it, just in case Murphy's Law happens to visit you.
Mark

Stephen H
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Post by Stephen H » Thu Dec 04, 2003 5:04 am

these things a EXTREAMLY loud and mabey to loud to be run for a contest! would be fun though, and you really gonna be going amazingly fast witha gokart, 100 lbs would be PLENTY for a gokart!

Stephen

TonyG
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Post by TonyG » Thu Dec 04, 2003 5:26 am

Yes, I understand that these things are extremely loud, and the inherent risks that come along with such a device. Unfortunately I have not actually been able to see one of these run, other then in video clips. I first became interested in the pulsejet engine about 3 or so years ago, but I didn't have access to the equipment to make one, so I had to put it off for a while, but now I have access to the needed equipment. I plan on using propane for the initial testing of the engine then running it off of gasoline, and using a small co2 tank mounted to the gokart to pressurize the gasoline so it will feed properly into the engine through an atomizer nozzle.
As far as the contest portion goes, I will enter pictures of the engine running, and possibly a video tape of it, along with the engine.
As soon as I get the valve design worked out, I will give detailed plans of it to a friend of mine who has been a machinist for Owens-Corning for the last 25 or so years, and he will machine them for the cost of the metal, if not for free.
I am open to any and all advice you might want to share about this project.

Stephen H
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Post by Stephen H » Thu Dec 04, 2003 7:15 am

TonyG wrote: using a small co2 tank mounted to the gokart to pressurize the gasoline so it will feed properly into the engine through an atomizer nozzle.
correct me if i am wrong here, but the vacume in the combustion chamber aswell as opening the valves for air it pulls the fuel though into the chamber so no pressure is needed? so the co2 tank wont be needed!

Stephen

TonyG
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Post by TonyG » Thu Dec 04, 2003 10:00 am

Stephen H wrote: correct me if i am wrong here, but the vacume in the combustion chamber aswell as opening the valves for air it pulls the fuel though into the chamber so no pressure is needed? so the co2 tank wont be needed!
I have read that it would, but then I have also read of not having a high enough flow rate without using some sort of pressurization method. I am thinking that fuel atomizer/sprayer I am looking at may require the fuel to be pressurized to work correctly.

Hank
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Sheet Gage

Post by Hank » Thu Dec 04, 2003 10:24 pm

Hello, TG- I do not know which gage system you are using to denote your sheet material. Let me state that if your material is a 20 gage of .032" you are using material that is too thin. You want .080" or better thickness for your duct. 304 is the right material. Strange as it may seem the thin material will implode.

I notice that some of the same old questions and wonderings appear as a new crop appears. Read this:

The correctly tuned pulse jet duct should be self-sustaining in its operation.There should be no need for external support as far as intake flow rate.

The pulse jet engine moves gases both ways (in and out) at the exaust end. This is the phenomenon that gives the engine compression.

The following is a description of a way to graphically check your duct for proper tune.
Draw your engine to scale in plane side view half-section (side view).
Describe two points at 1/7 duct length at the opposing points of the view from the intake end.
Draw a line from each of these points to the centerline at the end of the exaust duct. These lines should parallel the walls of the combustion chamber. If these lines intersect the combustion chamber your duct is not tuned correctly. The lines denote the mean lines of the thrust wave.
Now place two points opposing at the end of the exaust duct. Place a third point at 1/7 duct length from the intake on the centerline. Draw two lines from the opposing points at the end of the duct and meet them at the point you placed on the centerline 1/7 duct length from the intake.
The plane form of the conic section you have just described is the mean (averaged) line of the compression wave.

Please read some of the documents available on the internet regarding the operation of these engines.

Well, damn if I haven't earned dinner. Later, Hank

Graham C. Williams
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Post by Graham C. Williams » Fri Dec 05, 2003 12:52 am

Describe two points at 1/7 duct length at the opposing points of the view from the intake end.

Dear Hank.
What do you mean by this?
Graham.

Bruce
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Post by Bruce » Fri Dec 05, 2003 12:58 am

Something else to consider -- with an unoptimized pulsejet of that size, your fuel consumption will be around 800lbs per hour -- or something like two gallons a minute.

This means:

a) you'll need a fuel pump that can deliver 2 gallons a minute at whatever pressure your nozzles require

b) you'll have to pay for and carry at least four gallons of fuel for a brief 2-minute run.

Be warned also that you'll be spending a lot of time swapping valves in and out :-)

And don't stand directly behind that engine when it's running -- not only will it damage your hearing (regardless of the hearing protection you're wearing -- because it'll rattle the bones of your skull) -- but there's a very real risk that one of those valves will come loose and get spat out the back at a velocity that will cause it to slice into your flesh good and deep.

I believe that when it comes to *big* pulsejets, valveless engines are often a better alternative.

mk
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Post by mk » Wed Jan 21, 2004 9:04 pm

Hello.

Please don't misunderstand me, but I don't think that building a 200lb is a very good idea, 50 to 100lb would be more than enough for your first pj.

The biggest problem I see is the huge amount of the explosive mixture, especially during the starting process. If the relation between O2 and fuel is optimal your engine could splatter in pieces by igniting the mixture. If you don't consider this in construction, it can be really dangerous. Take a look at "www.aardvark.co.nz/pjet -> 100lb pj".

Another thing is the valve plate in such an engine. Making this for my 170N (~42lb) engine was a very time-consuming matter, it took almost 4 days of work. Work you don't see at all...

So I don't want to play "Mr. Headmaster" or s.th. and I think it would be great if your 200lb engine would finally run, but the problems aren't too small.

Valves:
If you are using V-valves, I would advice you to use a "V-angle" of about 30°. Don't forget the retainer plates, which will have to be at least half as long as your valves. Then plates should get some holes (just some little ones) spread over the area. They should get a curved form, by simply bending them along/over a 75...80mm diameter pipe, so they'll get the right angle (~15° when you take them as a straight line) and a kind of diffuser form as well. 30° of the "V-angle" are in my opinion optimal, because the completely opened valves won't decrease the valve-flow area, that can simply be calculated with a cos relation, if you know the real slit area under the valves.
Valves constructed like that are working very well in my tuned motorcycle engines.

Good luck

MK

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Post by cbromano » Thu Jan 22, 2004 6:27 am

MK-
How did you fasten the spring steel to the valve plate? Also- I am probably wrong but wouldn't the valves not carry enough momentum to go past a line parallel with airflow? I would think the retainers would not be necessary because the valves move a lot less then petal valves.

CB Romano
I don't wish to know everything.
I just wish not to be ignorant.

Eric
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Post by Eric » Thu Jan 22, 2004 5:35 pm

I agree that building a 200 pound thrust engine is not a good idea for your first engine. I would go for a 100 pound thrust engine and if that works well then maybe make a second one if you want your gokart to launch like a v-1... Remember that the V-1 engine only produces about 800 pounds thrust and even with the high mass of the missile it still reached very high speeds. Now take the power to weight ratio of your go cart and have 1/4 as much thrust as the v-1 and you are asking for problems.

Your frequency calculated from what I imagine to be equations from inside the pulsejet seem off. If you use my calculator it will give you a frequency of about 60 something hertz. This takes in effect the speed of sound in the high temperature pipe and works for every pulsejet I have found operational frequencies to compare.

As for the valve area it is the "theoretical" ammount that you would need to run the engine if the valve area was 100% efficient. With a valve grid the goal is to stuff as much valve area in the smallest space possible because no valve system is 100% efficient. Just put as much area as you can in the diameter combustion chamber supplied by my calculator and it should run well. If anything you can "tune it down" by making the retainer plates more restrictive. If you want help with the valve system I can send you some sketches of what you should do... email me if you want more info...

Eric

Pieter van Boven
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Post by Pieter van Boven » Thu Jan 22, 2004 5:54 pm

Hi TonyG,

For a big pulsejet like you want to built you should make a v-grid valve system I think. Here is a drawing of a V1 valve-grid. It's based on original drawings. Send me an e-mail if you would like to receive the CAD drawing.

Pieter.
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