SJC-Alien
Topic Author
Posts: 870
Joined: Wed Jul 14, 1999 1:15 pm

Smokey Start-ups........

Wed Mar 22, 2000 12:31 pm

I've noticed over the years, that some jet aircraft engines emit a large volume of smoke(blue in color) from the engines after start up in the AM,,,rarely in the PM.

This occurs on 737-300/500 series,,,,never seen it on a -400 series. Some Airbus, 757 and also the L-1011 when they were in the later stages before most airlines quit using them.

I've never seen this on 727- or a 747 or a DC-10
after a start up.

Why do they smoke and how come it's usually on low /under wing engine pod aircraft? Am I wrong?

SJC Alien



 
Danny
Posts: 3714
Joined: Thu Apr 25, 2002 3:44 am

RE: Smokey Start-ups........

Wed Mar 22, 2000 7:43 pm

Here are my thoughts:

1. Since there is some kind of "fire" in the engine on start-up, there should be smoke.

2. It seems to happen more on cold days, or in the AM as you mentioned. Could it be the hot, humid air condensing in the cold, dry air? Just like the "smoke" coming when we breathe when it's cold.

And, here are some pics to show the smokey start-ups. By the way - the 727 and the DC10 (actually MD11, but...) can have a smokey start-up.


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Photo © Richard Austen



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Photo © AirNikon



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Photo © Mathias Henig



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Photo © Darcy Stevens



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Photo © John Sidorowicz



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Photo © Jonathan Derden



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Photo © Søren Geertsen



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Photo © Sean Codier


 
dnalor
Posts: 346
Joined: Fri Mar 10, 2000 7:58 pm

RE: Smokey Start-ups........

Wed Mar 22, 2000 9:07 pm

Hmmm, at first I was tempted to say it might have been oil accumalation, but then I believe Kerosine or its cousin Avtur1 can give off a white vapour when heated sometimes.
 
Guest

RE: Smokey Start-ups........

Thu Mar 23, 2000 7:12 am

From the terrace at LGW you get an excellent view of the rear of the engines at start-up. The ones which I have noticed to produce large amounts of smoke are L1011, 777 and Virgin's ex Air NZ 747-200. I also notice resonance during start up on the 777 and the 747-200 with RR.
 
woodsboy
Posts: 899
Joined: Sat Mar 18, 2000 5:59 am

RE: Smokey Start-ups........

Thu Mar 23, 2000 8:09 am

The Rolls Royce RB211 series is well known for its smokey start-up behavior. This engine is a common thread on the L-1011 (all L-1011s have RB211s), 757s (they employ the RB211-535 with some airlines) and many 747s that belong to foreign operators which are the ones I notice to be RB211 powered. The TriStar is perhaps the most notorious "smoker" although this doesnt suggest mechanical problems or old engines.

Aside from that I have also seen P&W powered 757s (Delta) have some pretty smokey starts, the colder the air temp the smokier! But as the photos suggest many a/c and engine types can produce billowing clouds of smoke.
 
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tjwgrr
Posts: 2010
Joined: Fri Mar 24, 2000 4:09 am

RE: Smokey Start-ups........

Fri Mar 24, 2000 4:20 am

I believe it has something to do with fuel that is vaporized but not ignited.
Direct KNOBS, maintain 2700' until established on the localizer, cleared ILS runway 26 left approach.
 
FDXmech
Posts: 3219
Joined: Sun Mar 19, 2000 9:48 pm

RE: Smokey Start-ups........

Fri Mar 24, 2000 5:41 am

Nice pictures. Actually the United 727 isn't a smokey start but condensation being exhausted from the air turbine starter during the initial motoring up of the engine during the start sequence. The vapor is escaping the confines of the cowling. Often times this happens after it rains.
You're only as good as your last departure.
 
aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm

Dewpoint...

Fri Mar 24, 2000 5:58 am

like FDXmech said, water being vaporized in the engine, whether it be due to rain, or the temp reaching the dewpoint earlier that morning is the most likely explanation....

aaron
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Smokey Start-ups........

Fri Mar 24, 2000 7:57 am

The white vapour that is emitted from the jet pipe can have two sources.

1. If the ignitor (spark) plug is worn it can be slow in lighting off the fuel so you see fuel vapour.

2. If the engine is an RB211, the fuel system has a Fuel Enrichment valve to assist with eng starts. this vlv allows additional fuel into the engine until the N3 reaches 54%. It is this additional fuel vapour you see on start.

If the smoke is blue it is oil that has leaked out of a bearing compartment in the hot section & is being burnt.

If the "smoke" is prior to light up then it is as FDXmech says.
 
BigGiraffe
Posts: 256
Joined: Sat Jan 29, 2000 7:58 am

RE: Smokey Start-ups........

Fri Mar 24, 2000 11:00 am

While the RB211 is making white smoke during startup it is also making a distinctive vibration which fades away when it gets up to speed. What is the cause of that?
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Smokey Start-ups........

Fri Mar 24, 2000 4:48 pm

I belive it is the harmonics between the 3 spools as they pass through specific RPM range's

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