flame arrester on a jet engine
 

Dear all,

What is the purpose of the flame arrester on a jet engine?

On what jet engine? You mean the wire mesh around the exhaust you sometimes see on airport vehicles?

The only flame arrester I've ever heard of on a jet engine is the stopcock. :}

Fuel dumping systems have flame arresters to prevent a flame flowing back into the pipes/tanks. Fuel dumping is not generally done through engines though. (although it is possible through a shut down one)

Flame arrestor

Could be terminology used causing confusion.

If you are talking afterburner jet engines used on fighter planes the more common terminolgy that I have seen is "flame holder"

At any rate what they are used for is to keep the hottest part of the flame inside the engine where it can raise the energy /pressure of the gas before a duct area change (nozzle) that changes the energy into thrust.

If you didn't have a flame arrestor/holder than the air velocity within the engine woud carry the fuel droplets aft of the nozzles (either turbine inlet or afterburning) and you would continue your burning too far aft to be of use (nice blowtorch effects but quite inefficient)

The flame arrestor/holder is designed to create local turbulence which in turn increases residence time of the fuel within a given engine area so that you complete combustion of the fuel spray where it was intended.

well that's a start, let's see what else folks can add

Are you confusing yourself with the term flame arrestor used in Fuel Jettison and venting outlets?
Usually a wire mesh placed at the outlet to stop the ingress of flame.

Upon further cognition, I AM aware of such a flame arrestor. It's in the sump vent of some engines, when said vent is via the exhaust centerbody. It's to prevent a tailpipe fire (unburned fuel through the turbine stages) from igniting a oil sump fire.

There is a photo of such a vent arrangement in this thread.

Dang, I could have written those words sometime in a prior millenium! :O

Flame arrester
 

Could it be that the original question really meant "heat diffusers" as used to reduce the chances of getting a SAM up the jetpipe? Remember Air Rhodesia using such devices on their Viscounts in the late 70's - early 80's.

That's the beauty of the technical section of Pprune. A guy comes in and asks a simple technical question using some jargon which they heard someplace. Us technocrats know that there is an answer someplace among us if we guess at the meaning behind the question. So we have a go at it

The winner is not the best answer it's the best guess at what the question really was :)

Now what's the chances that the guy who asked the question will actually come back and tell us whence the question and in what context?

Meanwhile the casual readers hopefully have learned something new from the myriad of answers.

In my years as a technical instructor - and even as a F/I before that - this was often the hardest part of my job: Sorting out what the student was REALLY asking.

BTW - no matter how well I prepared to teach, I soon found the students would learn as much or more from each other, than they learned from me. The best I could do was to keep them steered in the right direction! :}

Meanwhile the casual readers hopefully have learned something new from the myriad of answers.

..which is why most of us don't fuss too much over thread creep etc. Some of the twists and turns I have seen over the past few years have been utterly fascinating.

Now, the only problem is remembering a small part of what is rolled out in the forum ... Seniors' Moments take their toll, I guess.

Certainly have :)

It amazes me sometimes what I learn on here and thats without having to learn to fly a plane too.

ok,

To further clarify the question it was in a ATPL piston eng/gas turbine exam;

it was something like this " what is the purpose of a flame arrester"

the options where along the lines of; used for when fuel SG increaces due to temp getting colder

and the other 2 options something alongs the lines of pipping to the engine???

You call that clarification!!!:}

Thanks to the other posters I remember now that on the Spey 250 we used jet eflux to drain the combustion liner through a pipe and a little holding tank then a pipe sticking into the jet pipe. There must have been a flame arrestor in there somewhere.

At 40 am I too young to be forgeting this stuff?

Thanks

Pick any of the answers above to explain what pipping is all about :}

The above are what makes PPRUNE so special, the banter is all part of the fun. I thank God everyday that I am employed in the aviation industry even if I am only a lowly engineer. Don;t take life too seriously!!!