Anyone know why?
Why some jet engines smoke when starting up?
- Thread starter Exhaustgases
- Start date
Probably incomplete combustion until the flame is completely established in the burner. Lots of them will have white smoke at first as they're blowing through unburned fuel until the ignitor's come on and the flame catches.
All down to how they are programmed to start I would imagine. The older and less sophisticated engines might just plow a ton of fuel in there to get them to catch, where as newer units are probably much more precisely controlled.
All down to how they are programmed to start I would imagine. The older and less sophisticated engines might just plow a ton of fuel in there to get them to catch, where as newer units are probably much more precisely controlled.
The turbo props on the Embraer Brasilia don't like cold weather and sometimes crank for an extended period of time before they catch. When they do catch, every mosquito within 5 miles dies.
Older jets did this a ton, even during takeoff. Just look for photos of a B-52 or 707.
MolaKule
Staff member
It all depends on how the FADEC is programmed. Older engines did.not have the closely controlled engine parameters as do modern engines. The original engines on the B52 did not have the combustion efficiency as do modern engines.
Propflux01
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T56 engines won’t smoke bad on start unless one or both igniters aren’t firing, or a lab seal is bad, as fuel and ignition are turned on at the same time.
Those pictures of black smoke on takeoff are due to water injection.
What purpose does water injection serve on a turbine engine?
A cursory reading of this article seems pretty accurate.
Lots of turbines used it, either that or a methanol/water mixture:
https://www.airwaysmag.com/new-post/explained-takeoff-power-water-injection
A favorite image of mine, I used to have a print hanging in my office. American Airlines 707:
It depends.
Seafoam or MMO. /Sarc
Its all the unburnt VOC's before ignition. Now I'm wondering how many tons of those VOC's are emitted everyday.
Agent Jayz was asked the question, why the white smoke at start up.
Agent Jayz was asked the question, why the white smoke at start up.
MolaKule
Staff member
"According to Newton's Laws., a jet engine develops thrust by imparting Momentum to the fluid passing through it.
I.e., Momentum = Mass of air X Velocity of the air. The sum of the momentum of the bypass air + the momentum of the exhaust gas gives rise to the total thrust of the engine."
Post #10 https://bobistheoilguy.com/forums/threads/molakule-q-a-on-aircraft-structures-vii-engines.396971/
Water or water-methanal injection adds mass to the airstream, so according to the Momentum equation above, this causes thrust to increase.
Here are some additional reasons:
1) condensed water vapour being heated giving off steam
2) partial combustion of fuel
3) pooled oil burning off
Again, very few modern engines smoke on startup or in flight because of improved oil seals and better control of engine parameters by the FADEC. The FADEC monitors engine parameters via various sensors and controls actuators and sends and receives signals to and from the flight deck, flight data recorder, and other devices that may be connected to ARINC buses.
I.e., Momentum = Mass of air X Velocity of the air. The sum of the momentum of the bypass air + the momentum of the exhaust gas gives rise to the total thrust of the engine."
Post #10 https://bobistheoilguy.com/forums/threads/molakule-q-a-on-aircraft-structures-vii-engines.396971/
Water or water-methanal injection adds mass to the airstream, so according to the Momentum equation above, this causes thrust to increase.
Huh? Where did you get this info?
The question has been answered in many ways.
Here are some additional reasons:
1) condensed water vapour being heated giving off steam
2) partial combustion of fuel
3) pooled oil burning off
Again, very few modern engines smoke on startup or in flight because of improved oil seals and better control of engine parameters by the FADEC. The FADEC monitors engine parameters via various sensors and controls actuators and sends and receives signals to and from the flight deck, flight data recorder, and other devices that may be connected to ARINC buses.
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Now I can't find that particular video, just saw it the other day. He said it was unburnt fuel.
MolaKule
Staff member
See post #13.
I’m reading about water injection. It allowed cooling of the mixture and a lot denser exhaust at the expense of efficiency. So at least when that was used, total thrust would increase, but that required a lot more fuel, where much of it wouldn’t completely burn and could come out as smoke.
MolaKule
Staff member
And reading through the posts, how did water injection increase thrust?
