Visible Turbine Flames
Joined: Jan 2006
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From: In a far better place
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
About 20 seconds into the start sequence.
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
About 20 seconds into the start sequence.
Joined: Mar 2002
Posts: 4,569
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From: Florida
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.
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.
Thread Starter
Joined: Jul 2006
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From: London
Originally Posted by MarkerInbound
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.
Thread Starter
Joined: Jul 2006
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From: London
Originally Posted by 18-Wheeler
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
That's a nice, quick start as well.
YouTube - Starting a Garrett turboprop engine
That's a nice, quick start as well.
Have you seen this one: YouTube - TNA Metro Startup
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
Joined: Jul 2001
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From: Gold Coast
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.
Engine uses "auto fuel enrichment" during start causing flashing until start is complete.
Thread Starter
Joined: Jul 2006
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From: London
Originally Posted by 18-Wheeler
It's explained in that video ->
Originally Posted by 18-Wheeler
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
Joined: Jul 2001
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From: Gold Coast
I won't pretend to know anything about fuel injection, is there a particular reason why the fuel is pulsed into the combustor?
Joined: Dec 2007
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From: Southeast U K
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.
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.
Joined: Jul 2001
Posts: 1,611
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From: Gold Coast
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.
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.
Thread Starter
Joined: Jul 2006
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From: London
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
Thread Starter
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From: London
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
Obi
Obi
Joined: Mar 2002
Posts: 4,569
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From: Florida
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
Obi
Obi
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From: US
Registered User **
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From: USA
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.
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.
