Re: Surge on GE90

From:         nak@gwe486.cb.att.com ()
Organization: AT&T GBCS/Bell Labs
Date:         21 Jun 95 02:56:59 
References:   1
Followups:    1
Next article
View raw article
  or MIME structure

In article <airliners.1995.773@ohare.chicago.com>,
Wayne Dockery <wdockery@pipeline.com> wrote:
>
>I have a question... When an engine such as the GE90
>is starting, what controls which direction the combusted
>material is expelled from the combustion chamber?  I guess
>the fan is electrically spun-up with "starter", but when
>ignition first takes place as in any "explosion", how do
                                       ^^^^^^^^^
First off, it's combustion, not an explosion.  Explosions involve
supersonic shock waves, combustion does not.

>you control which direction the expanded gases are expelled
>from the engine?  Is there some sort of mecahanism which
>governs the fan & compressor from turning in one direction
>only?

You provided most of the answer already.  When the engine is turned by the
starter, there is positive pressure at the front due to the compressor
stages compressing.  There is negative pressure at the back, due to the
turbine stages rotating.  The fan, compressor, and turbines are often on
the same rotating shaft - the starter spins them all.

At the onset of combustion, the gas flow will go more towards the low
pressure turbines and less towards the high pressure compressor.  That flow
will provide torque to the turbine.  If things go normally, there will be
more torque at the turbine than back pressure created torque at the
compressor and the engine will rotate faster in a positive feedback loop
until it comes up to speed.

>Also, are there any books available to the general public
>regaarding how the modern turbo-fan engines work.  I've been
>to the Nat'l Air and Space Museum in DC but there just wasn't
>enough information available other than the generic diagrams
>indicating what takes place in the various engine stages (fan,
>compressors, combustion chamber, etc).

Check your metropolitan library.

--
Neil Kirby	DoD# 0783	nak@archie.cb.att.com
AT&T Bell Labs  Columbus OH     USA (614) 860-5304
President Internet BMW Riders
It's very red.  It's very fast.  And it's mine: 1994 R1100RSL