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Visible Combustion

Posted: Sun Sep 12, 2004 2:28 am
by rg828
The other day I was photographing a 737-200 takeoff, directly behind it, and was surprised to see flames in the form of a ring deep inside both engines.



I never knew that the actual combustion was visible on any jet engine - airliner engine that is - Is this typical?

Thanks,
RG

[Edited 2004-09-11 19:32:43]

[Edited 2004-09-11 19:58:12]

RE: Visible Combustion

Posted: Sun Sep 12, 2004 3:00 am
by rg828
Come to think of it, I have seen the same thing looking at an A300 taking off at night.

Cant imagine seeing this on a GE90.

RG

RE: Visible Combustion

Posted: Sun Sep 12, 2004 3:33 am
by SlamClick
I think you captured a rare sight there. Logically, there is fire up in there somewhere but after a lifetime of occasionally looking straight up the tailpipe I've never seen this on a non-afterburning engine.

I suppose it would take a high power setting and maybe low ambient light to get to see this. Normally, the gases drop below the temperature where it would be visible like this.

Well done.


RE: Visible Combustion

Posted: Sun Sep 12, 2004 3:38 am
by dl757md
What you're seeing is likely not combustion rather it is the aft turbine stage blades glowing because of the extreme heat they are subjected to at T/O.

Dl757md

RE: Visible Combustion

Posted: Sun Sep 12, 2004 3:55 am
by SATL382G
Are you sure you're seeing flames and not just a hot part of the engine glowing?

I have a hard time understanding why people (especially aviation enthusiasts) are surprised to realize that combustion is a part of the process in a jet engine. If they see combustion going on at the front or rear of an engine (which is not normal but not unknown either) it's an "emergency". Check out the recent PIA engine fire thread to see what I mean.

SATL382G




RE: Visible Combustion

Posted: Sun Sep 12, 2004 9:27 am
by G4Doc2004
On the early series LearJets powered by the CJ-610-6 engine, you could easily see the flames from the combustor can at night during start. There was also a glow from the HP turbine vane ring.

Not that I advise this, but.:D......................if you stand behind any turbine engine at night during start, you can see the combustion process. I've done it several times over the years and using caution to not get too close and stand upwind of the tailpipe efflux, this can be easily observed.

RE: Visible Combustion

Posted: Sun Sep 12, 2004 11:29 am
by greasespot
Turbine blades do not get hot enough to glow. Even on T/O. I would have to look it up but I believe the max temp. Of the JT8 on TO is like 635 or something similar. Which is way below the glowing temp of the metal in turbine blades. It has been a while since I did power runs so I am not sure of the exact temp on T/O any more. If they did they would soften and melt.

GS

RE: Visible Combustion

Posted: Sun Sep 12, 2004 11:44 am
by Mr.BA
To add to this I recall the days when SQ had the A343s, when I was there to see the heavy take-offs overhead I noticed all 4 engines have the redish glow from the back... just wondering what is it that is glowing?

RE: Visible Combustion

Posted: Sun Sep 12, 2004 11:47 am
by airplay
I have seen the "ring of fire" looking into the aft of turrbine engines during a start, but never during takeoff. I guess I've never felt the need (or desire) to stand that close to an engine at such high power settings...

During the start, I've seen eratic flames that eventually turn into an even ring, and then disappear totally as the engine spools up to idle.


RE: Visible Combustion

Posted: Sun Sep 12, 2004 1:53 pm
by MD11Engineer
Sometimes the injection nozzles get deadjusted and produce hot spots. Normaly the combustion should be completed by the time the gases reach the turbine. Sometimes the injetion nozzles don´t produce a fine enough spray, causing a hot streak into the turbine. I´ve seen it quite often at night on CFM 56 engines on 737-300 when the plane taxied out. Also the RR Tay has a reputation for spitting flames at certain RPMs on start up, often accompanied by a coughing sound...

Jan

RE: Visible Combustion

Posted: Sun Sep 12, 2004 3:23 pm
by L-188
Confirm on the CJ610 story, spooked me the first time I saw one startup at night. Also saw it once on a Falcon 50 at the hanger next door.

On turboprops seen it on PT6's and TPE-331, but if you want a good fire show watch somebody pull the "E" handles on a Merlin on a ground run.

And I have seen the same "ring of fire" during the startup of an Alaska 737-200.

On takeoff no.


RE: Visible Combustion

Posted: Sun Sep 12, 2004 4:17 pm
by sovietjet
I have a video of an Il-62 on takeoff at night when you could clearly see the whole tailpipe is orange like an afterburning jet.

RE: Visible Combustion

Posted: Sun Sep 12, 2004 8:51 pm
by EMBQA
Turbine blades do not get hot enough to glow. Even on T/O.

What...?? Take a look up the back side of an ATR-72 next time its Prop Brake is on.

RE: Visible Combustion

Posted: Sun Sep 12, 2004 10:02 pm
by SDFOH
I've seen the "ring of fire" on all sorts of a/c, from a metroIII on engine shutdown to the glow from the apu on a crj200. Admittedly you can only see the crj apu glow in the dark from about 5ft. You can see part of the ring since the pipes have a crook to them

RE: Visible Combustion

Posted: Mon Sep 13, 2004 2:08 am
by LAXinYYZ
Interesting timing because yesterday I saw 4-6 foot flame coming out of the no. 1 engine on an EMB-145 at startup. It lasted for no more than 10 seconds, but I thought this could be normal. However it was noon and clearly visible, so I guess that this may not have been all that common.

RE: Visible Combustion

Posted: Mon Sep 13, 2004 10:10 am
by air2gxs
We see glowing turbine disks on our CFM56's all the time. Its common for that type engine.

RE: Visible Combustion

Posted: Mon Sep 13, 2004 10:13 am
by rg828
Thanks for the feedback guys.

Cant really say whether its the turbine blades glowing red-hot, but to me they look more like flames coming directly from the injectors. Sort of like blow-torches forming a ring.

MD11Engineer:

A friend of mine saw the same thing from an Fokker 100, and I remember seeing real flames come off a 707 I was aboard.

I thought that on recent engines the entire combustion process would be hidden inside the engine, but then a JT-8 is'nt really that recent anymore. An A320 departed before the 732 and there was nothing visible, and I looked very hard!




RE: Visible Combustion

Posted: Mon Sep 13, 2004 11:11 am
by dl757md
but to me they look more like flames coming directly from the injectors.

You wouldn't be able to see the flames in the combustion chambers as they are ahead of the turbine section. It could be flames that are exiting the turbine due to incomplete combustion in the cans that you are seeing but I stand by my previous suggestion that it is the high heat in the turbine that causes the orange ring you see.

Although it didn't really clear this debate up for me I found the following link quite interesting.
http://www.rolls-royce.com/education/schools/journey/flash.html

Dl757md