Brian B

My Feedback: (5)

A few of my buddies and I have been discussing an interesting topic. We are wondering what would happen if you were to fill the smoke tank on your Roo, or Hotspot, etc, with gasoline instead of smoke fluid. Would it ignite, or not? One school of thought says that it would ignite and produce a tail of flame behind the plane. The other opinion is that the exhaust plume is so deficient in oxygen that it would not ignite. None of us are so foolhardy as to actually try this, since the dangers are very obvious. It is an experiment best performed in the mind rather than in the real world. But we still wonder what would happen. Anybody have an informed opinion on this?

Just to be very clear on this: We are NOT going to try this, and are NOT recommending that anybody else try it.

John Redman

My Feedback: (8)

Brian B,

I can personally tell you it will not ignite at all. My guess is that there isn't enough oxygen for ignition as well.

tankie

what about O2 from the bypass etc?

seanreit

My Feedback: (60)

I'm with John on this one, not enough o2. That being said, don't think you should be afraid to run the test on an open engine application (roo, hotspot). There can't be any feed back in the burn because the tubes have no oxygen in them. Best case scenerio you'll get some cool flames, worst case it will do nothing.

Your smoke tanks will be fine for all the trouble, but try to keep the over spills etc to an absolute minimum cause that part will be highly flamable. Let us know what you find !

XJet

I'm not familiar with the smoke systems you're talking about but I am familiar with afterburner design.

Without a flame-holder, the chances are that it will not igite -- or at least if it does, it will go out almost immediately.

The problem isn't a lack of oxygen (there's plenty of unused O2 in the exhaust of a properly designed gas-turbine engine) -- the problem is that the gas in the tailpipe is travelling *much* faster than the propogation speed of the flame obtained by burning gasoline in air.

In effect, this means that the flame will be blown out.

The purpose of a flame-holder in an afterburner is to provide an area where the speed of the gasflow is *slower* than the speed of the flame-propogation. This results in an area where the flame will not be blown out, and means that the air/fuel that passes over the flame-holder will have a constant source of ignition available.

The other problem you'll almost certainly have is that you need a *lot* of fuel to keep an afterburner going. When you look at how much fuel is required to form a stoichiometric (combustible) mixture with just a small portion of the air that's used in the primary and secondary zones of the engines combustor, you can see that you'd need several times that to obtain a similar stoichiometric ratio with the remaining oxygen in the bypass airflow which is used to dilute the combustion gases and which appears in the tailpipe.

When I added an afterburner to an engine that had a 42mm compressor wheel, it consumed over a liter of fuel a minute when running optimally.

EddieWeeks

I am with EJet.. If there is no O2 how does a real afterburnner work.. ?

Eddie Weeks

Lt. Dan

My Feedback: (21)

Attempting to run an afterburner setup on an open mount is useless. You need a nozzle to capture the thrust created by the afterburner, otherwise, you are just igniting fuel in the open air and the expanding gasses will disperse in all directions.

XJet

The effect would be just like the one you get when the fuel vent is opened on an F-111 so that raw fuel is dumped into the jet efflux. It looks great but does nothing to increase the thrust :-)

Plenty of pictures like this one over at: http://www.f-111.net/airshows/

tetons9

My Feedback: (8)

xjet is right. just a little trivia info, A real F-15 carrys approx 2500 gal of JP-4 ( depending on the configuration). If it flys in full afterburner constantly it will use its total fuel load in about five minutes.

Larry

FalconWings

My Feedback: (57)

Eddie,

I think that on most modern AB, there is some bypass air flowing from the LS compressor directly into the 'tailpipe". This bypass air should contain enough O2 to cause the fuel to ignite.

This is the only reason I can think of. The expanding gasses on the exhaust loose internal energy (enthalpy), tis is due to loss in pressure, therefore the only way to ignite should be to provide O2 from the bypass air.

Now, can somebody tell me weather the RR Olympus (the engines on the Concorde) were T-jets ot T-fans? They do have AB's, but if they are T-jets it beats the hell out of me how they work.

patf

My Feedback: (4)

some of the euro's are using diesel fuel for smoke in the same setup... so if it ignites, which i doubt it would not be of any benefit.

EddieWeeks

I don't know about the RR Olympus, but the Mig 21 was a turbo jet with an afterburnner.

Eddie Weeks

Thud_Driver

My Feedback: (1)

All the early fighters (Century Series, etal) with AB's were turbojets equiped with burners. Wasn't til the F-111, or there about, that they figured out how to equip a turbofan with an AB.

BTW, I've used diesel fuel with an additive for smoke and it doesn't light off. Even if it did, it would be flames with no thrust.

S E Repton

Have a look at this link,

I think it should help to answer some questions,

http://www.aardvark.co.nz/pjet/turbine3.htm

Sheridan

MAX EFFFORT

some company [ in germany [ i think ] , makes an r/c size turbine with a working ab. not sure of the name .. they have a web site...do a search.. not legal at ama feilds i,m sure.

Woketman

My Feedback: (6)

SKYPIPE!!!

S_Ellzey

Turbine engines do not consume all the O2 that comes in. A very large part of the air that comes in is used to cool the combustion products down to the point that it will not melt the engine. The trick in the combuster is to keep the super hot gasses from touching anything until more air is mixed in behind the fire. So there is a fair amount of O2 left for an afterburner. You can get higher augmentation from a turbo fan since there is a larger amount of O2 in the exhaust.

At low power I have seen guys light off the smoke oil, but, as already mentioned, at higher power it gets blown out. At the Southwest Rally one guy landed with his smoke on, at touch down the oil ignited for several seconds.

Steven

wojtek

My Feedback: (73)

http://www.voy-tech.net/Videos/MB339/flamesall.wmv


this efect is acomplished by injecting smoke oil into the exhaust while the engine is starting up .. once running, the engine will blow the fire out as per what S_Ellzey mentioned, and what you can see in the vid clip .... it looks even better with a bifuricate dpipe exhaust


Wojtek

Johng

My Feedback: (4)

No need for bypass air, assuming anything is a perfect reaction -such as using all the o2 is not a good assumption. I don't remember much from Jet & rocket class, but the fact that the afterburner makes use of the largely uncombusted air coming thru the engine is one of them. The other was that the afterburner is essentially taking a ramjet and grafting it to the tail end of a turbine engine.

I also am reminded of the little story in Yeager's book about using one jet's exhaust to spin another fast enough to start. Park 'em nose to tail. It was T-33's or F-86's or something. If there's no O2, that doesn't work.

MAX EFFFORT

yes wocketman ,, thats it,, SKYPIPE is the company that makes an r/c turbine with afterburner.. do a search on SKYPIPE..

CARBUNCLE

anyone ever seen a skypipe being flown?

CFII1974

My Feedback: (5)

Wojtek - you get the same effect if you run an old RAM on a l-ion with no regulator .. look really cool on a test stand at night.

I-NAV

My Feedback: (3)

I saw a Skypipe while stationed in Germany. The flame and sound was like the old pulse jet days. It was heavy though. Had a stainless exhaust about a foot long. Thrust increased about 50 percent while fuel consumption went up 200%. Not what I'd call efficient, but fun to watch. I'm pretty sure Skypipe is no longer in business.

I'd not try the gasoline idea. You're going to have a very combustable cloud (read: fuel/air munition) behind the airplane.

Mike

wojtek

My Feedback: (73)

wont ignite ... don't ask me how i know ... learned one lesson !!!! MARK YOUR CANS WITH WHATS IN THEM !!!

lugebob

I am still trying to simulate the flame and burner pops of an afterburner on the jet luge.. I cannot get anything to ignite in the exhaust once the p200 is at idle. One of the Jet Car guys suggested that I add a seperate injector on a timed solenoid just in front of the Turbine wheel and to time the flow for .1 seconds. He calls this a Hot Streak and it sends a tongue of flame out the turbine into the AB of his GE J-79 to "Light His Fire". Does anyone now anything about this... is this even possible in a P200.

bob[link=http://www.jetfiretruck.com/sitebuildercontent/sitebuilderpictures/.pond/dsc_7561_std.jpg.w300h199.jpg]Jet Fire Link[/link]