Visible Turbine Flames [Archive]

Obi Offiah

1st Jul 2009, 22:01

I was just wondering, under what circumstances are flames visible (from the rear end of course) around the turbine blades, excluding turbine fires?

This video shows a centrifugal jet with visible flames: YouTube - Jet Engine Backyard - Episode 2 (http://www.youtube.com/watch?v=moX6Lps9w70)

This photo shows flames in the turbine sections of an F414 powered Super Hornet (I think the engines are set to military thrust not minimum reheat):
http://www.news.navy.mil/management/photodb/webphoto/web_060807-N-6106R-140.jpg

Here is the link for a high res version of the photo: http://www.news.navy.mil/management/photodb/photos/060807-N-6106R-140.jpg

Thanks
Obi

muduckace

2nd Jul 2009, 02:47

High Temperatures....

lomapaseo

2nd Jul 2009, 03:29

I seem to recall that we covered this in the last 3 months in this forum, the subject had something to do with flame arrestors etc.

Intruder

2nd Jul 2009, 03:44

Depends on the engine.

The old J-65 with a single turbine stage threw visible flame outside the tailpipe on start in daylight. These days, with multiple turbine stages, you'll likely see them only at night at high power, or when looking directly down the tailpipe as in your photo.

Tmbstory

2nd Jul 2009, 07:44

Reminds me of the old joke about two eagles sitting on a branch, side by side,as a jet went by with afterburner on. One said to the other " you would scream too if your ar.e was on fire like that".

Tmb

henry crun

2nd Jul 2009, 08:00

Obi Offiah: Please resize that photo so we don't have to scroll to the right to view it, thank you.

18-Wheeler

2nd Jul 2009, 09:55

Not quite what you're after, but I've seen right up the tailpipes of a 747-400 a couple of times, when they were taking off out of Cairns on runway 15. The procedure there has you starting the turn at 400' so very early, and where we parked the plane in the morning it was perfectly placed so we could see right up the back of the engines as the aeroplane banked around.
Just for a second of two, I could clearly see four bright-orange glowing donuts, one per engine.

Obi Offiah

2nd Jul 2009, 17:40

lomapaseo

2nd Jul 2009, 19:12

Thanks for resizing the pic

The flame you see is the afterburner lit (behind the engine turbine) and is typical for an afterburning engine at high power.

Most flames that you may see in the back end of non-afterburning engine under power are abnormal and pretty much signal a sudden loss of power while the flame is visible.

Flames during startup or shutdown are completely different thing,

Obi Offiah

2nd Jul 2009, 20:32

Thanks for resizing the pic
No problem :ok:

The flame you see is the afterburner lit (behind the engine turbine) and is typical for an afterburning engine at high power.
I'm pretty sure this it is not an afterburner flame because firstly it is too deep within the bypass duct, i.e upstream of the spraybars. Secondly for a carrier launch (particularly this far down the bow), either the engines are at military thrust or maximum afterburner. In either case due to the possibility of a flameout/stall the afterburner igniters would be energised and visible. Thirdly when set to low/minimum afterburner it is the central circular V gutter channel that is lit as well as the igniters as in the following picture:
http://www.news.navy.mil/management/photodb/webphoto/web_080402-N-2838C-003.jpg
High Res version here: http://www.news.navy.mil/management/photodb/photos/080402-N-2838C-003.jpg

The following is another picture in which the turbine flame is visible (just barely) possibily due to the brighter ambient light condition:
http://www.news.navy.mil/management/photodb/webphoto/web_090630-N-6854D-001.jpg
High Res image here: http://www.news.navy.mil/management/photodb/photos/090630-N-6854D-001.jpg

Obi

lomapaseo

2nd Jul 2009, 20:48

Obi

I'm pretty sure this it is not an afterburner flame because firstly it is too deep within the bypass duct, i.e upstream of the spraybars. Secondly for a carrier launch (particularly this far down the bow), either the engines are at military thrust or maximum afterburner. In either case due to the possibility of a flameout/stall the afterburner igniters would be energised and visible. Thirdly when set to low/minimum afterburner it is the central circular V gutter channel that is lit as well as the igniters

Well you seem to have a lot of experience in this from reading the above. So I had to go back to your original questiom to form my answer

I was just wondering, under what circumstances are flames visible (from the rear end of course) around the turbine blades, excluding turbine fires?

The only time that flames would be visible that far forward arround the turbine blades at high power would be in the event of simultaneous dual engine failures which seems not to be the case in your photos. So I chalk it up to optical allusion.

What do some of the others carrier deck folks see? Is it normal or not? Are these really flames or just glowing hot?

Obi Offiah

2nd Jul 2009, 20:57

The only time that flames would be visible that far forward arround the turbine blades at high power would be in the event of simultaneous dual engine failures which seems not to be the case in your photos. So I chalk it up to optical allusion.

:ok: cheers, I'm starting to think the same. Also it could be that visually it is very sensitive to ambient lighting which has a huge impact on the appearance of the flame, perhaps a little like how an afterburner flame changes appearance depending on ambient light. It looks completely different in low light conditions as to broad daylight.

Obi

Will Fraser

2nd Jul 2009, 21:27

Generally the Iris is fully open with any AB setting??

18-Wheeler

2nd Jul 2009, 23:23

No no 18-Wheeler thats pretty interesting. You mentioned that you observed this in the morning, under what sort of lighting, was it low light or dim conditions?

I think it was about 6am or so, so call it low-ish light I guess. I'm pretty sure the effect could have been seen under full daylight though if you were at just the right angle.

Must upload some vids I have of starting the Garretts on the rattly old Metro's I used to fly - They get up a frighting glow. :)

Obi Offiah

3rd Jul 2009, 19:08

Generally the Iris is fully open with any AB setting??

Hi Will
The VEN variable area nozzle/Iris has an area that varies depending on throttle settings, flight conditions, atmospheric conditions and engine condition. Generally speaking the nozzles are fully open (or close to fully open) at ground idle. At military power they are near fully closed. As the afterburner is selected they begin to gradually open from mil setting and continue to do so as maximum afterburner is selected. At maximum AB they are near fully open under optimal conditions.

The reason the nozzles at max AB are not fully open under normal circumstances is that additional 'margin' is needed to ensure the engine can operate safely with require performance throughtout the flight envelope. Also on a hot day an engine will make less thrust so the nozzles are set with a smaller area than on a cold day where more thrust is avaliable.

Obi

Obi Offiah

3rd Jul 2009, 19:22

I think it was about 6am or so, so call it low-ish light I guess. I'm pretty sure the effect could have been seen under full daylight though if you were at just the right angle.
Hmmm....so there must be some other factor at play here, because sometimes you can get very similar lighting conditions and view the engine/s from a very similar angle yet not witness a glow.

muduckace mentioned high temperatures, so perhaps an engine running hot due to a low EGT margin could be a contributary factor?

Must upload some vids I have of starting the Garretts on the rattly old Metro's I used to fly - They get up a frighting glow. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif

Please do, I look forward to seeing those.:ok:

Obi

John Marsh

3rd Jul 2009, 20:46

What can produce flickers of light visible from the front of a JT4? I saw some whilst on a B707-320. There were no accompanying noises.

lomapaseo

4th Jul 2009, 00:26

What can produce flickers of light visible from the front of a JT4? I saw some whilst on a B707-320. There were no accompanying noises.

Wow you must have a long memory :)

I have seen similar flickers associated with reverser operation and reingestion of ground debris into the outboard engines while turning off the runway . This went away quite a few (50) years ago with better reverser techniques.

MarkerInbound

4th Jul 2009, 03:44

Are we really seeing flames? Metal glows red hot a bit above 700C, I think it's just the last turbine wheel. I've taxied behind 727s and 737s and seen the engine light up when the power is puched up.

18-Wheeler

4th Jul 2009, 05:01

Good timing for the thread to come back up, I found a video of the Metro starting, and here it is.

YouTube - Starting a Garrett turboprop engine (http://www.youtube.com/watch?v=DvshBFJSoDo)

That's a nice, quick start as well.

Hmmm....so there must be some other factor at play here, because sometimes you can get very similar lighting conditions and view the engine/s from a very similar angle yet not witness a glow.

I guess it would depend on the amount of derate used as well. Full derate has the engines running a fair bit lower EGT.

John Marsh

4th Jul 2009, 12:57

lomapaseo: Thanks for your reply.

The 707 was in the cruise, at night, in 1989. Two periods of bright yellow/white flickering from inside the engine, each period less than a minute.

Storminnorm

4th Jul 2009, 15:17

Sounds like some sort of surging problem?
But in the cruise? A bit unlikely.
707, just knackered motors I reckon.
Never had that sort of thing in the DC 8.

captjns

4th Jul 2009, 15:25

Too many too young to remember the good old CJ610 that powered the original Lear Jets, Jet Commanders, Jet Stars, Sabre Liners just to name a few.

When ever you heard one of those motors cranking up and the igniters clicking you only stood behind the exhaust once, and only once. 3 foot lick of flame would come out of the back when light off occured. Pretty exciting to say the least, especially for the chap standing behind the engine.

YouTube - Learjet CJ610 Turbojet Engine In Test Cell (http://www.youtube.com/watch?v=zo4E8ndfEoA)

About 20 seconds into the start sequence.

lomapaseo

4th Jul 2009, 15:29

The 707 was in the cruise, at night, in 1989. Two periods of bright yellow/white flickering from inside the engine, each period less than a minute.

Ah, a great deal more info:ok:

Well it probably wasn't reverser operation :}

The color yellow is significant (most reports are bright white sparks)

White would go with titanium blades (being FODed or rubbing their tips against the case). Yellow goes with steel blades. If its arround their tips its rubbing (screwed up bearing) if its random then its chewing up something loose like a rivet or a stone. Common on the ground but not at cruise.

Obi Offiah

4th Jul 2009, 16:47

Are we really seeing flames? Metal glows red hot a bit above 700C, I think it's just the last turbine wheel. I've taxied behind 727s and 737s and seen the engine light up when the power is puched up.

On occasion there is are small licks of flame around the turbine wheel, but your correct it is mainly a red hot glow.

Obi Offiah

4th Jul 2009, 18:18

Good timing for the thread to come back up, I found a video of the Metro starting, and here it is.

YouTube - Starting a Garrett turboprop engine (http://www.youtube.com/watch?v=DvshBFJSoDo)

That's a nice, quick start as well.

Nice video.:ok:

Have you seen this one: YouTube - TNA Metro Startup (http://www.youtube.com/watch?v=pvws8az8rok)
In both videos after combustor ignition the turbine wheel begins to pulse for some reason. After a few moments the pulsing stops and the turbine wheel glow becomes stable. A few moments later the turbine glow disappears despite the engine still running.
I think part of the reason for this could be associated with temperature spikes which are quite normal during engine start-up, also a the combustor fueling profile (rich start mixture perhaps) could also contribute.

Obi

18-Wheeler

4th Jul 2009, 23:08

In both videos after combustor ignition the turbine wheel begins to pulse for some reason. After a few moments the pulsing stops and the turbine wheel glow becomes stable. A few moments later the turbine glow disappears despite the engine still running.

It's explained in that video ->

Engine uses "auto fuel enrichment" during start causing flashing until start is complete.

The Garretts pulse in more fuel to accelerate the engine faster during start. with doing that they'd either hang or take about two minutes to start.

Obi Offiah

5th Jul 2009, 00:41

It's explained in that video ->
Cheers.:ok:

The Garretts pulse in more fuel to accelerate the engine faster during start. with doing that they'd either hang or take about two minutes to start.

I won't pretend to know anything about fuel injection, is there a particular reason why the fuel is pulsed into the combustor?

Obi

John Marsh

5th Jul 2009, 09:37

Storminnorm, lomapaseo: thanks for the info.:ok:

18-Wheeler

5th Jul 2009, 09:52

I won't pretend to know anything about fuel injection, is there a particular reason why the fuel is pulsed into the combustor?

I'm not really sure, but there's a computer that controls the engine start sequence and EGT red-line limiting. I guess that's just the way it's programmed - But I agree that I can't see why it just couldn't run a pre-programmed EGT for engine acceleration during start anyway.

Storminnorm

5th Jul 2009, 11:05

Never heard of fuel pulsing on start-up.
FCUs in my day. None of this computer
controlled MECs rubbish.
I can probably ASSUME that the fuel pulsing
has something to do with the 'Burn rate" of
kerosine.
Don't want to bung in too much motion lotion
whilst the engine establishes itself at idle RPM?
Otherwise the candle goes out.

18-Wheeler

5th Jul 2009, 13:20

No, you can see the fuel-flow pulsing regularly and the EGT follows this. It's all part of the plan.
When I flew the even-more rattly POS Metro 2's that didn't have any electronics on the engine for starting or limiting the EGT, I had to push the 'ENRICH' button myself, and I too would often end up pumping it in a similar manner to what the computer does on the later engines.

Obi Offiah

6th Jul 2009, 13:02

Ok, I've done a bit more searching (thank you Google) and it seems that two reasons for the pulsing are that its a method of controlling the combustor/turbine temperature as 18-Wheeler mentioned. Also the pulsing programme is a very easy to impliment open loop controller.

Obi

Obi Offiah

13th Aug 2009, 20:57

I've just discovered the following video on youtube. Its from the external camera in the vertical fin of a B-777, showing the turbine glow from both GE90 engines: YouTube - GE90-115B (http://www.youtube.com/watch?v=UgCkaf0FrW8)

Obi

lomapaseo

14th Aug 2009, 00:02

MU3001A

14th Aug 2009, 02:58

Daytime view.

YouTube - Contrails (http://www.youtube.com/watch?v=X2zPEyaOTMo)

muduckace

16th Aug 2009, 04:55

Some not so great memories of used and abused engines here but the fact still stands, under normal ops modern final stage turbine exaust may glow due to temp/metallic alloy.

The only reason otherwise would be excess fuel in the turbine section during start, engine failure or after burners installed in mostly military aircraft.

Another note..EGT is only relevant to the position the engine manufaturer decided to install the "rakes" or sensors at. The exaust gas temperature varies throughout the T-stages and tailcone.