Expert: Capt Paul - 2/4/2007

Question
Hi Capt. Jeeves, heres a video of a rolls royce engine water ingestion test.

http://youtube.com/watch?v=faDWFwDy8-U

How come the engine doesn't flame out or stall will all the water being taken in? How much water would it need to flame out?

Answer
Hello Kevin,

The first question.. “Why does it continue to operate…?  Basically, the engine is enclosed inside a cowling.  The part of the engine that you actually see is simply a propulsion fan.  The air that goes into the actual engine is re-routed several times and compressed to extremely high pressures and tempuratures.  This process of re-routeing and the high pressure / tempurature, eliminates most of the water that goes into the combustion section of the engine.  Albeit, this is a very basic explanation, and I haven't discussed the ignition modules, etc.  

Other types of engines also use devices such as "particle separators" which take advantage of the kenetic energy of the passing water droplet to deflect it away from the engine (not used with the Trent 900).

As far as the amount of water needed to flame-out the engine, I don’t actually know.  Basically, the Trent 900 engine (like most other engines) was required to pass an EASA rain and hail ingestion test.  That test (for the Trent 900)  requires that -  for three minutes -  the engine must continue to run while a flow of 118,000 litres of water per hour is pumped into the engine, thus simulating torrential downpours and runway conditions in the tropics during monsoons.  The engine did not surge, flameout or deteriorate, therefore it passed the testing requirement.

Sorry that I can’t give you a better answer.

Cheers