Pulsejet Variation Question

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Rbuck
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Pulsejet Variation Question

Post by Rbuck » Sun Apr 06, 2014 6:56 pm

Hello,
I am building a pulsejet engine. But during construction I started to wonder about some things.

About The Pulsejet
Firstly, it does not use a petal valve. It uses four shutters, 1/8-inch thick steel sheet metal, each 2 inches across (for an overlap of 1/2 inch between shutters).
The shutters are vertically oriented and symmetrical.
My pulsejet casing is simply a 6-inch-bore steel pipe. I may (have to) narrow it down into a 3- or 2-inch tailpipe.
I punched holes in the pipe end to fit 1/2-inch steel rods. I plan on using 1/4-inch rods, bent at the end, to secure the shutters to the rods.
I have some basic questions on this, such as
1. Will it work?
2. What kind of fuel will it take, and what sort of fuel injection system can I use?
3. How much power can I expect from it?

Preamble
While I was doing research for the jet, I and my grandfather came across a YouTube of somebody flying a FUTURA jet. My grandfather told me it used a ramjet. But I had seen it taxiing around on the video, and ramjets require forward movement to generate thrust. So I wondered... I'm building a pulsejet, what happens if I slap a large air intake onto it? If I put an intake onto my jet, it would accelerate the air through the combustion chamber. Now, surely if the air goes fast enough it will tend to force the valve open even during the combustion shockwave. Wouldn't my jet (with a little adjustment for fuel feeding) effectively become a ramjet? So I looked up ramjets, but all I found was that they operate at a minimum of .5 Mach. However, none of my sources appeared to have intakes on their ramjets... which gave me a headache trying to figure it out.

The Big Question
Well, what does happen, in terms of thrust, efficiency, coolness, etcetera, if I try to make my engine a pulsejet/ramjet? I've looked online, but all I found was some half-hearted "I'll have to try this sometime" answers in response to a guy who had wondered the same thing on a site called the "half bakery". So maybe you guys out here could say more?

Epilogue
I may build a test vehicle, sort of like a go-cart, to test this idea.
Thanks in advance!
Okay, here's my idea... Now let's see some of you bright engineering minds shoot it to pieces.
I'll be keeping score.

Rbuck
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Re: Pulsejet Variation Question

Post by Rbuck » Sun Apr 13, 2014 10:56 pm

...hello? Anybody home?

Has everybody no better idea than I of this system?
Or are people testing it even as I type? :wink:
Okay, here's my idea... Now let's see some of you bright engineering minds shoot it to pieces.
I'll be keeping score.

metiz
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Re: Pulsejet Variation Question

Post by metiz » Sun Apr 13, 2014 11:05 pm

There aren't a lot of people left on this forum unfortunately Some knowledgable people are still lurking around you know who you are! I know you're watching! :lol:
I'm not an expert on valved designs (...or valveless, realy...but I digress) but I MIGHT be able to answer some of your questions. It would help if you drew a picture (Sketchup?) to make your idea clear. Just from the getgo, even though I don't realy understand your shutter-valve idea: 1/8" is realy thick. That's a lot of mass to move in a very short amount of time (hundreds of times a second)
Quantify the world.

Mike Everman
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Re: Pulsejet Variation Question

Post by Mike Everman » Sat Apr 26, 2014 3:28 pm

Hello rbuck,
A straight pipe will not work. I suggest you look to Eric's pulsejet calculator and learn a few things about the proper shape of the duct.
As to thick and heavy valves, again, you are taking things in the wrong direction. They must be light as possible, while still strong enough to contain the pressure pulse.
Mike
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