Motor Jets!

Jets that defy normal classification

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Chadly33
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Re: Motor Jets!

Post by Chadly33 » Tue Sep 30, 2008 12:02 pm

Hmmmm? Yes well thanks for that.lol Just kidding! This is still very early stages, I was just experimenting with the whole idea of the vortex combustion to see if I could set up the self sustaining stable vortex. This is only a mixing, or initial combustion chamber for the engine I am still working on the rest of the engine design. I am only taking baby steps with this one and trialing different ideas as I go. :D
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racketmotorman
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Re: Motor Jets!

Post by racketmotorman » Tue Sep 30, 2008 8:44 pm

Hi Chad

Theres a guy Charlie currently on DIY Gas Turbines thats been sucessfully using a "similar" combustor for his turbine engine .

He's feeding the air in axially and then thru swirl vanes to create the "vortex".

Might be worthwhile checkin out his progress in the "New Photos" ..... http://tech.groups.yahoo.com/group/DIYGasTurbines/spnew

Though I can't see why he/you can't use more "traditional" ways of obtaining efficient combustion .

All the best with the trials :-)

Cheers
John

Chadly33
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Re: Motor Jets!

Post by Chadly33 » Sat Oct 04, 2008 3:26 am

Ok! Now have done a bit more, the original CC has now become a frst stage CC or mixing can that sets up the vortex and starts the combustion. This is now joined to a ramjet style body to allow for extra expansion. I still need to get more air into the engine to produce any great amount of thrust but the thrust increase from combustion is evident when I stand behind it. The secondary CC is only tacked together and tacked onto the first stage CC so will also have to finish this off before anything real will happen as I turn the fuel up it pressurises out the joins!lol I took a video of the combustion with the fuel down really low so I could get close enough to film it but even at full zoom the camera was starting to get hot so I had to stop!(not my camera)lol :lol:http://www.youtube.com/watch?v=U-6GQDXed2I
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Mike Everman
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Re: Motor Jets!

Post by Mike Everman » Sat Oct 04, 2008 6:08 am

racketmotorman wrote:Hi Chad
Theres a guy Charlie currently on DIY Gas Turbines thats been sucessfully using a "similar" combustor for his turbine engine .
He's feeding the air in axially and then thru swirl vanes to create the "vortex".
Might be worthwhile checkin out his progress in the "New Photos" ..... http://tech.groups.yahoo.com/group/DIYGasTurbines/spnew
Though I can't see why he/you can't use more "traditional" ways of obtaining efficient combustion .
All the best with the trials :-)
Cheers
John
Charlie's is a neat idea. To my mind it's better than a tangential duct. For a pulse combustor, though, different story? The way I see it is that there's damned little time for any tangential flow to get around the CC very far no matter how you set it up. And I'm going to assume that any flow structure is gone with each pop.
Just some generalities: If the inflow was 100 m/sec on average, and the chamber were say 100mm dia, and the frequency of the motor were 150 Hz, then there's 6.7 milliseconds per cycle, and the time that there is an actual inflow is 3.35 msec at 100 m/sec is .335 meters. So our tangential flow is approximately 1 revolution around the CC.
So "not very far" is about a full circuit. More than I thought, but still doesn't seem like much. Faaaascinating.
Mike
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racketmotorman
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Re: Motor Jets!

Post by racketmotorman » Sat Oct 04, 2008 7:29 am

Hi Chad

Interesting video :-)

Thrust is a function of the square root of absolute temperatures .

If your "blowers" are producing a certain thrust with ambiant air at ~300 deg Kelvin , then at say 2,500 deg K ,( about the max temp possible ), you'll only be able to obtain ~2.8 times the thrust of those base blowers despite burning huge quantities of fuel .

By the "colour" of your "combustor" , I doubt you've got half that max temp , so roughly twice the "ambiant/cold " thrust of the blowers ...............have you measured their "cold" thrust ??

Cheers
John

Zippiot
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Re: Motor Jets!

Post by Zippiot » Sat Oct 04, 2008 9:12 pm

I noticed that not much was happening in the center of your CC. What do you think adding a cone or rod to fill the space would do?

Otherwise it looks really cool, or hot.
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Chadly33
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Re: Motor Jets!

Post by Chadly33 » Sat Oct 04, 2008 9:52 pm

The flame vortex actually tightens and is visible at higher fuel settings but it is impossible to get close enough to video it due to heat. You can see it in the centre of the engine quite clearly at these higher settings the addition of a tube or cone would interupt this I think. :?
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racketmotorman
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Re: Motor Jets!

Post by racketmotorman » Sat Oct 04, 2008 10:56 pm

Hi Chad

Could you please explain why you "need" a vortex to obtain combustion , it appears to be a waste of internal energy to me .

What you currently have have is an afterburning "gas turbine" , your "compressor wheels "( fans) are being driven by "turbines" ( electric motors) , with the products being "burned" in a tube to increase temperature ,(with no increase in TOTAL pressure) for a velocity increase over "cold" operations due to the improved thermodynamics from the increased temperature , a bog standard turbine scenario.

That being said , you need the most efficient "afterburner" design to maximise your thrust output , and a vortex doesn't appear to satisfy that requirement .

I'd strongly suggest a different approach based on "standard" aero gas turbine afterburner design if you wish to maximise your output :-)

The fact that you are using pressurised gas as fuel with its own energy for the intimate mxing of it and the air , negates to a large extent the need to provide mixing by making the air "move about" ( vortex) with its attendant losses.

You're already running a very limited total energy in the air supply , any losses will soon degrade it to the point where the engine won't work , you need to supply the air to the combustor in the most energy efficient manner possible to maintain its total pressure because its that total pressure which makes thrust , not the heating of the air ........
no excess total pressure ........no thrust, no matter how hot the flames are :-)

Cheers
John

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