Supersonic Propane nozzles

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Supersonic Propane nozzles

Post by Viv » Thu Jan 22, 2004 11:07 am

As the propane nozzle is one of the most critical components in the pressure jet I thought I would start a new thread to discuss it and its design, the job of this nozzle it to produce a stream of propane gas moving at supersonic speed.

Liquid propane is first fed in to the heat exchanger coil, this turns the propane from a liquid to a superheated gas at about 1200f

This gas is then expanded through the nozzle at the supply pressure (100psi off a normal tank) down to the pressure in the first inlet stack element (less than ambient?)

Expanding the gas through the nozzle lowers its temperature, if the gas had not been preheated to such a high temperature first it would have turned back to a liquid as it left the nozzle! see the teperature plot in the link below.

Its this supersonic stream of propane that will drive the engines operation, it not only entrains air as it passes down the inlet stacks to provide a stoichiametric mixture for combustion but will also help to compress the mixture along with the pressure waves from the engines natural resonance.

I will start another thread to discuss acoustics and how they influence the engine.

The pressure in a normal propane tank is decided by the vapor pressure of the liquid propane, thats about 100psi so unless a pump is available thats what we have to work with:-)

The pressure in the top of the first inlet stack element will be a bit lower than ambient due to the vacuum caused by the gas stream entraining air, but we do not have any measurements for this as yet, its this figure and the supply pressure that will decide the maximum velocity of the gas through the nozzle.

The design rules for DeLavel rocket nozzles apply but the DeLavel is not the only type of nozzle that can be used, what about the airospike?

This link to a NASA page looks very promising and also has some very important mechanical advantages.

A free technical pack is available to registered users but you have to be US resident to register! if some one in the US could download it and email it I would be grateful.

The attached image is probably copyright to Nasa

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Post by Rossco » Sat Apr 03, 2004 7:46 am

Hey Viv. Good thread

I had a play with some consepts of supersonic nozzles with air conditioning gear.

I was thinking of making a pressure jet of my own loosely based on an old patent i saw in a book years before. I didnt have any dimensions or reall idea of allowable tollerances. But in my opinion at the time i had a perfectly sound idea of the whole concept.

With the exeption of the super sonic nozzel.

I don't think at the time i had any pulse jets running. (my first attempt, a now amusingly out of proportion little chineese that was just never going to run!)

Nevertheless i thought that i was capable of producing a pressure jet straight of the top of my head. Even though i didnt know that was what it was at the time!
So i started playing with some liquid/gas flow ideas.
Do you just have to buy these things?
I froze a lot of things, and had lots of fun with different gases, but never had much success.

I was pumping gas with a compressor to about 300 pound through a check valve into a condenser. An old copper tube one that i converted into a heat exchange over a fire. I didn't have a gauge to see pressure after that but in the end it busted my set up so it must have been pretty high. I played with a lot of different adaptions of fittings that i had at work, but didnt get anything as fantastic as i expected.
I gave the idea away and havnt gone back to it again.

Im not sure if i understand the concept still seeing the diagram.
I understand that the gas has to speed up toward the outer smaller area to maintain a constant flow at a higher pressure, i think, but then as it drops pressure does it not slow down and the energy is used by drawing in heat? Im confusing myself now, as its not a liquid at the higher pressure cause of the pre heating? So theres no change of state? and no energy change?
Does the convergance maintain pressure, or does the thing pulse?

how about you give me a quick rundown, or direct me to a good site or desription!

Thanx. Please exuse my ignorance.
Big, fast, broke, fix it, bigger, better, faster...

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