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Post by ernie wrenn on Feb 29, 2012 14:17:51 GMT -5
I fillally found a FULL afterburner with TURKEY FEATHERS!!! :0
Should have it next week.
ernie
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Post by Johansson on Feb 29, 2012 14:23:51 GMT -5
Want to share with us what you are smoking? ;D
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Post by Richard OConnell on Feb 29, 2012 14:38:15 GMT -5
and where exactly did we acquire one of these?
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Post by ernie wrenn on Mar 1, 2012 8:44:29 GMT -5
Do not drive that F-16 on the left corner of the lot.. Only right turns in A/B....
ernie
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Post by areacombustor51 on Mar 11, 2014 10:54:53 GMT -5
Water injection into jet pipe. I'am thinking about experimenting with this. Steam instead of combustable fuel. Will it have the same effect as a pushing force of hot burning fuel. Considering I don't know if the water injector will have enough time to turn water into a vapor. Just thinking here...
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Post by racket on Mar 11, 2014 18:35:23 GMT -5
The drawback of injecting water into the afterburner is it will drop the temperature of the gases as heat is used to vapourise the water spray , the reduced gas temperature will reduce the exhaust velocity as theres a direct connection between the two, water injection to cool the afterburner wall temperature is a different scenario where we are trading off the temperature drop for something else thats more important .
Water injection , or better still a water/alky mix , into the combustor is a "better" experiment to try , especially if the turbine stage is a little "oversized" as the steam could/will reduce the compressor flow into a more efficient region , this reduces the power required from the turbine wheel , which in conjunction with the increased mass flow from the water/steam will further reduce the "relative" power requirement , increasing jetpipe pressures for making thrust .
Gas turbines need "balance" between the needs of compressor and turbine for best results , its all about "hole sizes" throughout the engine .
Cheers John
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bob
New Member
Joined: December 2014
Posts: 3
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Post by bob on Dec 12, 2014 21:41:41 GMT -5
Sorry for the newbie resurrecting the dead but… I gotta know if it was tried!
My thoughts: Yes, water will cool the EGT. But I suspect not by enough to matter.
The burned gases in a jet are only 400-500X their original volume and are high quality heat. 1 liter of water converted to steam occupies a volume of 1700L at STP, plus water is reeeaaaaallly heavy. So given the specific heat of water, my guess is very little could be used and yet significantly increase mass flow.
I've found we tend to immediately think of exhaust gas temps only (ease of habit) when we think of thrust rather than m dot as we should.
Anyway, back to trying to find out how the Thud did it. Best to all in this holiday Season!
Bob
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Post by racket on Dec 12, 2014 22:22:40 GMT -5
Hi Bob
If only our burnt gases we're that many times bigger in volume , but volume changes with absolute temp changes , so if we start at 288 K - 15 degrees C and heat them to 2880 K - 2607 deg C they only change by 10 times ............at our 15 degrees C density is ~13 cubic feet per pound , at 2607 deg C its ~130 cubic feet per pound.
Using a mass flow of say 1 lb/s of hot gases in an afterburner at only ~2,500 deg F , thats ~600 BTU/sec , but to turn 1 pound of water into steam requires ~1,200 BTUs , even if we used only a minuscule 0.1 lbs/sec it'd require ~120 BTUs thus lowering our gas temps by 20% even discounting any extra BTUs required to get the steam up to 2,000 F
At most we can only expect minimal thrust increase with water into the afterburner , better to inject it elsewhere .
Cheers John
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bob
New Member
Joined: December 2014
Posts: 3
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Post by bob on Dec 13, 2014 18:12:57 GMT -5
Hi John,
First, thanks for having me in the forum. I do love this stuff. Next, sorry for the delay getting back, but my iPad kept freezing while typing.
Yeah, you're right. I was converting a 10-12 carbon liquid fuel to fully combusted gases. But you got to admit- not bad for on the fly and in my head!
But back to scavenging some of that quality heat... Am I right that one of the limitations of reheat is melting your tailpipe (so to speak)?
How about this- pump just enough water through the tailpipe to take it from white hot to a dark cherry and release it circumferentially on the inside of the tailpipe just downstream of the afterburners fuel injectors. I don't think much water would be required to do this (may be wrong tho). How far down I'm sure is related to diameter and the speed of the gases (and temp).
The steam(?) would form a new boundary layer against the tailpipe in effect insulating it from the higher heat of the combustion gases.
So I'm thinking "go ahead and overspool like crazy and dump everything you got into the afterburner stream- your thrust is only limited by the size of your injectors and you can spend all day in afterburner if you want!" (I know, but don't pick me apart here, I'm on a roll)
I'd be like dumping a chintzy Holley 2 barrel for a carter thermoquad- not efficient, but gobs of extra horsepower (or thrust in our case).
So not only could you burn waaaaay more fuel, you've added the water mass to the exhaust stream for even MORE thrust!
I can see plenty of problems here, one of which is that the steam would in essence form a "nozzle" like in a solid rocket motor and a reflected pressure wave slapping the back end of the turbine may not be a good thing. On the other hand, it may be a "tunable" thing (like long pipe headers) and obviate the need for an adjustable burner nozzle with its added weight and moving parts. On the other "other hand", that'd mean you'd have to carry around a lot of heavy water.
Still, I'm dying to know if the poster tried it. Also still trying to find out how the water injection in afterburner worked on the Thud... anyone?
Regards, Bob
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Post by racket on Dec 13, 2014 19:56:16 GMT -5
Hi Bob A small amount of water for wall "steam insulating" has already been discussed over the years, though I haven't heard of it being tried because no one has "melted" their A/B , they get pretty hot and glow, but still retain integrity, so no one has felt the need for wall cooling, our A/Bs use so much fuel that burn times are limited when installed on a kart, a big turbo like my GT6041 jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart with ~2.75 lbs/sec - 165 lbs/min of airflow will use ~11 lbs of fuel per minute on full afterburn assuming the usual 15 : 1 A/F ratio for complete combustion of the oxygen , thats over a gallon and a half , ~6.25 litres , of kero per minute . Our afterburner temperatures are limited simply by running out of available oxygen , we already burn it all , any extra fuel will probably only reduce temperatures due to the over rich mixture , our afterburners are at maximum thrust, theres no more to be had , we run virtually the same A/B temperatures as full sized military fighter jets. Any steam for wall cooling would be easily handled by opening the afterburner jet nozzle up by a couple of millimetres in diameter to restore the engines TOT temps to ideal design levels , it ain't a problem. Hope this helps explain things :-) Cheers John
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bob
New Member
Joined: December 2014
Posts: 3
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Post by bob on Dec 14, 2014 16:35:15 GMT -5
... ~11 lbs of fuel per minute on full afterburn ... So it's been a toss up b/w electric kart and finding a small junk turbo. But with my tendency to create catastrophic outcomes, I can't see that much stored energy as being anything but a bad idea. And given your numbers it doesn't sound like a very efficient mode of transportation. Doesnt matter much. The "gotta do" list seems just grow and grow leaving my "wanna do" list stuffed somewhere in the kitchen "junk drawer". But I'll bet it's a real kick in the seat of the pants to ride! Bob
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Post by smithy1 on Dec 15, 2014 13:49:42 GMT -5
I can vouch for the "thirstyness" of the 6041 powered kart....I'm the sucker who has to feed it's appetite now ..She only carries ~9liters of fuel so run times are very limited indeed.
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