Jet engine question #1: flame holder

Jet engine question #1: flame holder

Joined: January 17th, 2007, 11:41 pm

March 2nd, 2012, 1:53 pm #1

Hi,
can anyone explain how the flame holder device in the afterburner of a jet engine works? Originally, judging by its name, I thought that this is where the fuel was injected and hence it "holds the flame" there. A closer look revealed that this is actually not true, on y J-79 for example the fuel injection nozzles are in the space between the rear turbine and the flame holder. The ignition torch however is where the flame holder is. So how does it work, how and where does the flame holder "hold the flame"?
I would understand if the fuel was injected AFTER the flame holder and due to shock waves created by the flame holder there is a pressure differential and the flame will only travel to the exhaust nozzle (low pressure) and not to the turbine (high pressure near the flame holder). But with the fuel injected BEFORE the flame holder this doesn't really make sense to me...I would expect the fuel to burn in the area between turbine and flame holder.
Any ideas?
Cheers
Jeffrey
Hypersonic Models
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Joined: March 6th, 2005, 3:23 am

March 2nd, 2012, 6:45 pm #2

http://www.youtube.com/watch?v=1DdF3U2g-Ic

It kinda creates a area in the can that is like a pressure shelter so the Air does not blow ot the flame. I hope that makes sense, Darren
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Joined: January 17th, 2007, 11:41 pm

March 2nd, 2012, 7:27 pm #3

I've watched quite a few videos of this guy, but not this one! I think they're some of the best videos out there as far as technical insight, good explanation and walkaround detail go, especially with my favourite, the J-79. Did you notice, towards the end of the video when he films the burner can, how green the inner liner is?
He says that the flame holder forms an area of low velocity - does that not seriously hamper the engine's performance in non-AB operation? I basically thought that the purpose of the flame holder was to prevent the AB flame to cause any damage to the turbine, i.e. create a cool cushion between the turbine and the flame area. But what you've said about not blowing the flame out makes sense as well. Still not entirely sure why it's designed this way but I'm sure they would have designed it differently if there was any better way.
J
Hypersonic Models
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Joined: March 6th, 2005, 3:23 am

March 2nd, 2012, 9:32 pm #4

Yea, From what I understand is it keeps a buffer to hold the flame in place, kinda like in the Combustor cans. I think in the AB section, the AB is selected at full power, so cooling is more from the amount of air being pushed thru You gotta love the sound of a J-79. I was lucky enough to see the F-104G's fly, and the new jets are to quite for me
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Joined: April 10th, 2005, 1:32 pm

March 11th, 2012, 12:54 am #5

Hi,
can anyone explain how the flame holder device in the afterburner of a jet engine works? Originally, judging by its name, I thought that this is where the fuel was injected and hence it "holds the flame" there. A closer look revealed that this is actually not true, on y J-79 for example the fuel injection nozzles are in the space between the rear turbine and the flame holder. The ignition torch however is where the flame holder is. So how does it work, how and where does the flame holder "hold the flame"?
I would understand if the fuel was injected AFTER the flame holder and due to shock waves created by the flame holder there is a pressure differential and the flame will only travel to the exhaust nozzle (low pressure) and not to the turbine (high pressure near the flame holder). But with the fuel injected BEFORE the flame holder this doesn't really make sense to me...I would expect the fuel to burn in the area between turbine and flame holder.
Any ideas?
Cheers
Jeffrey
Hi again,
The flameholder keeps the flame centered in the pipe, simular to the flameholders on the stove. It also allows a airpath to keep the flame from touching the liners.
This poor piece of equipment, is usually beat up badly, severe cracking and distortion. There is a small tubr usually at the 5:00 position, aft looking forward, that is the Pilot Burner Can or Torch Ignitor. Inside this was the Afterburner spark ignitor and one fuel nozzle.
Today I'm a F110 mechanic and its all called Augmentor and Exhaust Nozzle.
Rick
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