First ramjet from scratch

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heada
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First ramjet from scratch

Post by heada » Sun Mar 11, 2007 5:39 am

So, here is my first ramjet design from scratch. I have the templates printed out and will start cutting some 22 ga mild steel to weld up (also my first time using a welder). I hope for it to be small enough to use high pressure air from my compressor. Initial fuel will be LPG but moving up to MAPP gas, kerosene, white gas (coleman fuel) and 20% nitromethane. I'll run each one with the same amount of air (as close as I can) and measure thrust on my 44 lbf load cell. I'll be using a spark plug and coil from the hobby aircraft industry to keep the hair on my arms intact.

Suggestions on flameholder placement?

Thanks,

-Aaron
Attachments
base ramjet.zip
dxf file in zip as dxf isn't allowed (why?) and the cad program I'm using wont let me export it to anything other than dxf
(2.08 KiB) Downloaded 723 times

Irvine.J
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First ramjet from scratch

Post by Irvine.J » Sun Mar 11, 2007 1:52 pm

Hi Heada,
I think the biggest mistake with my ramjet of similar design that I built was putting the flameholder right behind the aerospike. It really seems to work against your airflow and destroy any advantage that aerospike has given you in airspeed/ pressure terms. From looking at many other designs I'd advise to try initially putting your flameholder about 1/3 to 1/2 way down your CC. Probably start at 1/2 and move it foward if necissary, as many similiar designs employ the flameholder that far back with aerospikes, why? I don't know, I'm assuming you need to give the airflow time to revert back to a workable pressure region from that high velocity intake. It would be very interesting to see, if it works well for you I might change mine to that arrangement also. I'd say seriously try it smack bang 1/2 way down the CC, if you don't want to go that far not more then a few CM foward. Just tack weld it in place so you can dremel it off and move it if need be.

I hope you have a nice big petrol blower, it absolutely powers over the electric ones bar none.
Goodluck
James- Image KEEPING IT REAL SINCE 1982
http://pulseairdefence.com
[url=callto://project42labs]Image[/url]

heada
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flameholder

Post by heada » Sun Mar 11, 2007 8:24 pm

What was the design of your flameholder? I was thinking of using either concentric rings at a slight angle (think of a expanding cup, but in the flat mode) or a waffle pattern (lots of 90* angle iron, laid out so that the point of the angle iron is facing the incoming air)

I have a 2 cycle leaf blower that produces 245 mph air at 425 cfm. I was going to use my air compressor and a smaller version of this to test it out at high speeds. The air compressor with the blower nozzle should produce air flow near the speed of sound, just not very much volume. I'm also working on a 45 hp 4 cycle engine with a 48" bi-blade prop to create fast air AND high volume.

-Aaron

Irvine.J
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Flameholder

Post by Irvine.J » Mon Mar 12, 2007 3:30 am

I think the idea for the flameholder is good. Remember don't choke the walls and give it a bit of distance between the first ring and the wall of the CC. Your Angled rings will be pushing air outwards as it passes through, creating a nice pressure zone there anyway. Leave a small area in the centre that is not impeded at all too. If by angled you mean 1cm length cones or similiar you'll have a small divergent nozzle in the centre region which will work well.

I think you may need to make 2 or 3 flameholders of the same nature with different spacings/angles or 2 or 3 completely different designs. I think its more important to create a rolling vortex for mixing directly behind the flameholder then slowing down the airflow too much. Objectively I think it would be better using 6 to 8 small rings then 4 big ones, know what I mean? Make sure you calculate the surface area of those rings combined to the surface area that you have to work with, start with about a 1/3 third area and play from there.
Goodluck. Look foward to seeing how it goes.

Ps Your blower kicks @ss
Give it a little distance between the nozzle of the blower and remember you can taper the blower nozzle down. I used a big piece of rolled cardboard and nozzled it down to about 1.5/ 2 inches D, and wrapped the hell out of it in scotch tape. The airspeed coming out was awesome.
James- Image KEEPING IT REAL SINCE 1982
http://pulseairdefence.com
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Vermin
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Post by Vermin » Tue Apr 03, 2007 8:38 am

Hi Guys
Just curious heada have you used nitromethame before..... it is not nice stuff in any way shape or form, there are very specific aspects for the aplication.
Vern
A desire to destroy as many man made hydrocarbon compounds as possible in one lifetime.

heada
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NM

Post by heada » Wed Apr 04, 2007 6:51 pm

I've used 10% mix for R/C cars, but that was years ago.

-Aaron

Bill Lubarsky
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Test: Ramjet images

Post by Bill Lubarsky » Fri Apr 06, 2007 11:46 pm

Can you see them now?
(my fifth try).
WEL
Attachments
kitchen_ramjet_1.JPG
Kitchen with ramjet
kitchen_ramjet_1.JPG (53.11 KiB) Viewed 9434 times
kitchen_ramjet_2.JPG
Up the back end, classic sink strainer
flameholder
kitchen_ramjet_2.JPG (57.21 KiB) Viewed 9436 times

Bill Lubarsky
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Test: well that worked!

Post by Bill Lubarsky » Sat Apr 07, 2007 12:00 am

Not quite from scratch, but off-the-shelf and found components.

The diffuser and combustor part of the shell are from Burns Stainless:
a 2" ring, a 2"x4" megaphone and a 12" long section of tubing expanded at one end to an I.D. of 4".

The nozzle is a 2"x4" S/S concentric reducer from A and N Vacuum products.
The inlet is a 2" air amplifier I have played with for years, it is coupled
to the diffuser with a rejected thingy from the machine shop at work.

Internal plumbing (not visible) by McMaster Carr.
Attachments
kitchen_ramjet_3.JPG
Inlet.
Air amplifier and scavenged thing.
kitchen_ramjet_3.JPG (47.7 KiB) Viewed 9429 times
kitchen_ramjet_4.JPG
What every kitchen needs
kitchen_ramjet_4.JPG (58.44 KiB) Viewed 9435 times

Irvine.J
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First Ramhet

Post by Irvine.J » Sat Apr 07, 2007 5:46 am

MATE THAT IS A DOOSEY!
Wow am I impressed!
So are you injecting the fuel into the cavity around the outside of the flameholder? Very interesting indeed, if using propane this will probably may not combust completely... (Dont freak out i'm just thinking aloud)
And I'm sure your aware of this.

Give it run and post videos and pics, it should be pretty easy to see how its mixing once going. I JUST CAN"T WAIT FIRE IT UP NOW!

If you can't get it to run properly, try injecting your fuel 1/2 way along the big long inlet with a good couple of nozzles, (for instance a straigh copper pipe with a huge number of tiny holes so you can get plenty of flow.) (dont worry about soldering/welding it in, just rest it in there about 1/2 way up the inlet and hold it (or get a friend to) so its centre.

Ideally, when your FULL on your propane bottle, you want to be FULL ON out of the nozzles too :D

As always begin with propane. If your airspeed is high, and you throw a sparkler or 5 (twisted together to make a nice star looking thing) in the back of the engine, you should find the combustion is easy and wont beat that flameholder...which is sooo damn nice man. Nice build, nice work, and I'm looking foward to your initial tests.
James- Image KEEPING IT REAL SINCE 1982
http://pulseairdefence.com
[url=callto://project42labs]Image[/url]

Bill Lubarsky
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Not quite from scratch

Post by Bill Lubarsky » Sat Apr 07, 2007 1:30 pm

I didn't photograph the internal plumbing, it is maybe not what you expect.

The pipe nipple coming out of the side of the ramjet goes down to a "T"
fitting. A 6" long 1/4" pipe nipple goes toward the inlet and terminates
in a small spray nozzle. A 2" long pipe nipple on the back end ot the "T"
is capped and supports the sink strainer flame holder.

The fuel is sprayed upstream towards the inlet to provide a longer mixing
distance before it is burned, hopefully just behind the flame holder.

I don't see any problems starting the thing since continuous air will be coming
from the air amplifier, right up to the limit my 5 HP air compressor's tank in
full dump mode .I have close to 15 lbs Propane in a 600 psi rated tank with separate
valves for vapor or liquid. I can hook a Nitrogen cylinder to it and pressurize if need be.

I don't however have a video camera to record a test or neighbors who
could stand for me running the thing more than once! I will have to
get it the first time!

Please note that this is a direct-connected ramjet for test purposes.
There are two ways to test a ramjet: One way is to put it in a wind tunnel
with the design inlet and measure the free-stream operation
(like the engine is attached to an air frame and in flight.
This is true ramjet operation. You can also plug it into an
air supply (direct connection) andessentially run it as a honkin'
big blowtorch! What I will have to do.

Bill Lubarsky
Attachments
General Ramjet_1.jpg
(86.14 KiB) Downloaded 458 times

Eric
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Post by Eric » Tue Apr 10, 2007 12:44 am

Very nice job.

I would put the fuel injector farther up stream, pointed back, especially if your tank is being pressurized to 600 psi. There isnt much point having the propane fight the incoming air, and also if you run out of air or dont provide enough its going to push the flame way forward / right out the intake instead of nestled behind the flame holder.

Cant wait to see some pictures and video of it :)

Eric
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Talking like a pirate does not qualify as experience, this should be common sense, as pirates have little real life experience in anything other than smelling bad, and contracting venereal diseases

Bill Lubarsky
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First (cold flow) measurements.

Post by Bill Lubarsky » Fri Apr 13, 2007 2:28 am

I borrowed an anemometer from work today and measured the
airflow into intake of the air amplifier with ~120 psi compressed
air feeding the ejector. The air flow through the 2" inlet reads
about 32m/sec> I use about since the thing looks like a toy fan,
and has never been calibrated. The only good thing about the
anemometer is that the fan is 2" in diameter and can completely
fill ihe inlet. I don't think any air "snuck" around outside.
Now I have to give it back and get a pressure gauge.

WEL

tufty
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Post by tufty » Fri Apr 13, 2007 7:40 pm

Your air amp should give a 15:1 or so ratio, feed the amp propane and forget fuelling.

Or maybe I'm drunk

Simon

Bill Lubarsky
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Post by Bill Lubarsky » Fri Apr 13, 2007 10:03 pm

Tufty.

I tried that a long time back. It didn't work.
Air amplifiers don't work well against back pressure unless really
juiced with lots of hp air, then the ratio drops down to single digits.
Just propane gave me a blowtorch running really lean!!
Besides, I want to give it a chance to run somewhat in the mode of the
original NACA design...but without the Acetylene and the Mach 2
air stream.

Bill

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