"Fat Boy" 12/118 thrust engine

[racket]

Hi Patty

Thanks for the Link , the good old KJ66 has been used for a lot of "Papers" :-)

Theres so many variables with flametubes as well as the evap tubes that it gets to be a bit of a nightmare trying to reconcile all the conflicting requirements , especially when I've got such a short length to work with , the flametube needs to be twice as long .

On another video of the testrun theres times when small chunks of red hot metal are flying around from the exhaust , and "puffs of smoke" infrequently, something which I've never seen before , this engine has certainly thrown up some new issues to solve .

Cheers
John

[turboron]

John, as you know, getting it to run is just the first layer of the onion. Happy hunting.

Thanks, Ron

[racket]

Hi Ron

LOL.......lets hope its not a large onion :-)

I've taken the side grinder to the flametube and started removing the side walls , hopefully after a bit of a cleanup the front wall can be used again , as well as the inner rear wall, the rear wall with the evap tubes is easily modified to allow the securing screws that hold the flametube together to be used .

The wall axial lengths can be made the same , just a slight change in circumfrential lengths , it shouldn't take to long to modify .

Cheers
John

[turboron]

John, what is your planned corrective action? If it was a typical gas turbine high pressure fuel nozzle I would look for a plugged or partially plugged nozzle. I have no idea for a fix for an evaporator system.

Thanks, Ron

[racket]

Hi Ron

Yep , for a single spray nozzle it'd be a limited number of options , but considering I've got 18 injector, each one isn't feeding a huge amount, maybe 150cc/min at full throttle and only a fraction of that anywhere near the wall , but it could be several evap tubes supplying a bit of liquid each thats running around that gutter to set up a "blowtorch" .

I know theres a pressure drop across the flametube wall , but would it be possible for some fuel to be sucked out of the corner of the flametube from the gutter ,by the action of air passing around that tight corner near the shaft tunnel and setting up a flame on the outside of the flametube which would certainly overheat the wall to the point of failure .

The way the hole edges are burnt , with a lot of the remains inside the flametube on the edge of the hole sorta indicates a flame coming from outside the flametube .

Another thing , the "cold" thermocouple was downstream of the "hole" , so this might indicate excess air entering at that point , much more air than what could support combustion of any fuel exiting the closest evap tube

Remedial action , as I answered Tony ...............
Hi Tony

The wall was "seated" fairly tightly against the rolled edge of the front wall , so minimal chance of leakage , but there was an ~3mm "axial gutter" between the end of the sidewall and the front wall that fuel could accumulate in , and with the swirl being produced within the primary zone that fuel could move to a convenient position and possibly burn.

Yesterday I had a good long chat with Andy M about the problem and we've decided that the side walls need to be fixed to the "outside" of the endwall roll over rather than being "inside" , this will remove any chance of fuel collecting in that "gutter", it will simply flow from radial to axial smoothly and onto the side wall in a less concentrated state .

Also the evap tubes, which are currently "angled" towards the inner wall so that they exit roughly mid way between inner and outer walls , will be repositioned "axially" bringing their outlets closer to the outer wall which isn't suffering any heat issues.

The repositioning of the walls will also add a bit more to the flametube volume which won't be a bad thing as its kinda small at present .

The Secondary air holes might be displaced a tad further rearwards as well to increase the Primary Zone volume , and I might go for a single hole rather than twin holes between each evap tube to get deeper penetration and less chance of cold air contacting the evap tube .

I'll do a bit more thinking before cutting metal :-)

Cheers
John

[turboron]

John, the idea of fuel puddling being the problem does not sound right to me. A blowtorch is required to burn the metal I think. Just thinking out loud here based on experience. As you say, think twice and cut once.

Thanks, Ron

[racket]

Hi Ron

Totally agree , its needs a good sized flame to burn through 1.2 mm stainless, but I'm at a loss to find where its originating from :-(

I've cut the flametube apart and salvaged the front wall , just got a bit more cleanup work on the inner rear wall and it'll right to use again as well , so only a couple of side walls to make .

Cheers
John

[CH3NO2]

Mar 8, 2019 8:20:08 GMT -5 turboron said:

John, the idea of fuel puddling being the problem does not sound right to me. A blowtorch is required to burn the metal I think. Just thinking out loud here based on experience. As you say, think twice and cut once.

Thanks, Ron

Hi Ron,

That would do it but it needs a fuel source.
So the question is "How could fuel get there and from what?"
Dripping?
Oil from the CHRA?
Kero from the fuel supply?
Does the orientation align to gravity or a potential source?

There is likely to be a very high air velocity in that area.

A small recirculation zone with added fuel? IDK

It's plausible if things line up.

[turboron]

CH3NO2, good comments. I burned up a highly instrumented development engine late one night. The cause was bad oil seals leaking oil from the sump under the combustor. John, could a oil leak cause your damage?

Thanks, Ron

[CH3NO2]

Possibly a torroidal vortex/re-circulation zone enveloped around the entirety of the top plate inner circumference... but with added fuel or oil dripping/streamed into that one spot?

That may be possible, but why didn't the rolled over lip of the top plate also get burned?

Tony

[racket]

Hi Ron

I was going to pressure test the fully assembled shaft tunnel to make sure a seal/pipe hadn't failed as theres gotta be "fuel??" coming from somewhere outside the flametube .

LOL.............Hopefully theres a "reason" that can be easily fixed.

Cheers
John

[monty]

I wish I knew the answer, but...all I have to add is the area to the left looked overheated too. Too rich or too lean means colder. Is it possible airflow was not protecting the flame tube somehow?? That is really the only thing keeping the flame tube from melting.

[azwood]

I'm sure an answer will present itself soon it's an odd one but to be in just that spot.

[azwood]

Just a wild guess bus could it have anything to do with using petrol in the mix.

[turboron]

azwood, good question. Let's leave no stone unturned.

Thanks, Ron