taguilo
Posts: 73
Joined: Tue Aug 02, 2005 7:51 am

Engine Hung Start Question

Sat Apr 29, 2006 3:16 am

Hi all,

I understand a "hung" start happens when an engine is accelerating towards idle RPM, with normal combustion, and an extraction of bleed air occurs. So, the engine never reaches idle RPM but instead keeps running in a lower stage.
Question is, does it respond anyway to throttle movement?, I mean, if throttles are advanced, does RPM increase BUT with a lower than normal percentage indication, maybe with a higher than normal EGT reading, or not even accelerate at all?

Thank you
Tom
 
troubleshooter
Posts: 420
Joined: Mon Feb 07, 2005 5:22 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 3:37 am

A hung start happens if the engine stops accelerating towards the idle RPM or "rolls" back after reaching idle. The only correct action in this case is to shutdown the engine! Never advance the throttles in this case. As the airflow through the engine is too low you can easily overshoot the max. EGT (hot start)by introducing more fuel. Depending on the time of the EGT exeedance you´ve created some more trouble...  bomb 

I don´t know any aircraft type where you are allowed to advance the throttles during engine start (except moving the throttle lever to the idle detent on some types).
This job sucks!!! I love this job!!!
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 3:39 am

Been many moons since I dealt with a non-FADEC engine but I think I would believe that advancing the throtttle while in a high-EGT sub-idle would have the immediate effect of increasing the hot section temperatures and the long-term effect of shortening your career. I don't think it would have any significant effect on RPM.

There are others around here better equipped than I am to give you the technical stuff but I think it might be useful to think of this condition as being like 'dieseling' in a gasoline powered piston engine. It is not really running, as we understand that, but 'kicking over' as a result of a flame pattern the engineers did not intend.

The thing to do is deprive it of all fuel and perhaps to keep dry-motoring it for a time to clear the unburnt fuel.

[Edited 2006-04-28 20:41:20]
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
fr8mech
Posts: 6714
Joined: Mon Sep 26, 2005 9:00 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 3:43 am

Quoting Taguilo (Thread starter):
an extraction of bleed air occurs

An extraction of bleed air is only one of the causes. Air management (VBV/VSV), fuel control and substandard ignition can also cause hung starts.

As stated, never advance the throttle if a hung start is suspected. The increae in fuel can easily overtemp the engine. I suspect that a FADEC engine won't even allow an introduction of more fuel.
When seconds count...the police are minutes away.
 
troubleshooter
Posts: 420
Joined: Mon Feb 07, 2005 5:22 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 3:48 am

Quoting SlamClick (Reply 2):
Been many moons since I dealt with a non-FADEC engine but I think I would believe that advancing the throtttle while in a high-EGT sub-idle would have the immediate effect of increasing the hot section temperatures and the long-term effect of shortening your career. I don't think it would have any significant effect on RPM.

Hi SlamClick,
it is always a pleasure to read your posts!!!  bigthumbsup 
This job sucks!!! I love this job!!!
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 3:56 am

Quoting Troubleshooter (Reply 4):
Hi SlamClick,
it is always a pleasure to read your posts!!!

Thanks. My wife said I should edit my profile - 'hobbies' to include 'pontificating' What do you think?
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
troubleshooter
Posts: 420
Joined: Mon Feb 07, 2005 5:22 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 4:02 am

Always follow your wife, mate! Big grin
This job sucks!!! I love this job!!!
 
taguilo
Posts: 73
Joined: Tue Aug 02, 2005 7:51 am

RE: Engine Hung Start Question

Sat Apr 29, 2006 4:43 am

Thank you guys!

Actually what I need to do is program the expected behavior of the engine in a hung condition, IF throttles are advanced. I understand the non-FADEC 757 throttles would advance and inject fuel even if the engine doesn't reach idle RPM, however EGT would peak beyond limits, damaging the engine for sure if it is not shutdown on time.

Tom

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