10/98 engine

[Richard OConnell]

wow.. sorry to hear that. I was really looking forward to seeing it up and running with all the bugs worked out.. Any chance you'll be resurrecting this project?

[ernie wrenn]

How did the temp spike THAT high, that quick. The other runs were well in the safe range. Looks like the Stainless just gave way, looking at he stress cracks in the burner can.

Possible hot start? What a Bitch.. .that was a beautiful machining job.

I need to put up some pic's of a Rolls Royce 201 we blew inside the shop.... It is easy to see the radial damage in my shops ceiling..

Ernie

[racket]

Hi Richard
Yep, she'll be resurrected , just need a bit of new "tin work" and a cleanup , she was running so nice the other day , right up to 100% at 66,000rpm , at 61,000 with a comp tip speed of ~1475 ft/sec , she was putting out a 2.75 pressure ratio at 73% efficiency with a T2 of 150 deg C and a TOT of ~575 deg C .

Heres the "autopsy report " I posted on the DIY Site .......

....I've been having a real good hard look at things and it seems the flames have come out of the flametube to contact the shaft tunnel heat shield , it was hot enough to melt the ceramic blanket material inside the steel outer sheath .

Theoretically the flame can't come out of the flametube as there is a pressure drop across the FT wall and a lower static pressure inside the FT .

So far all I can put it down to is the lack of straightening vanes at the diffuser outlet , there is some straightening of flow from the cast in place vanes , but looking at burnt oil witness marks on the FT exterior it appears as though there is still considerable swirl around the FT .

Now for swirling air to travel from a large radius to a smaller radius, as it has to do from the diffuser outlet , down the back of the diffuser wall and in to the inner wall of the FT, its velocity has to increase and its static pressure will drop , exactly the reverse of the comp diffuser .

This decrease in static pressure could have been enough for the static pressure within the FT to be higher than the static pressure existing around the shaft tunnel , causing flames to exit into the space between FT and shaft tunnel , it appears as though the flames have then gone forward to contact the backside of the diffuser wall and up and over the front of the FT as there are witness marks showing where bits of metal have scraped surfaces ., also the edges of the FT wall at the failure have the rough edge outwards as well as molten metal "droplets" on the outside of the FT , all indicating an air/gas flow in the opposite direction to what it should be .

On my FM-1 engine I retro welded on "curved ears" at the FT outer edge opposite the diffuser outlet to direct air down the rear wall of the diffuser as there was some appearance of heat stress on the inner wall of the FT , the 9/94 engine had a FT with "ears" opposite the diffuser outlets and still had a "hot" inner wall , but I put it down to the FT not being very far from the diffuser wall restricting the turning of airflow at the diffuser outlets , the 10/98 has its FT displaced further rearwards due to the large scavange oil gallery on the back of the diffuser wall and I didn't feel it needed any "turning ears" ................guess I was wrong :-((

Straightening vanes as well as some sort of curved deflector required ...........................thankfully no major damage to the turbine wheel , some buildup of metal on its tips and a fairly bad rub where the blades turn from radial to axial ( in the corner) , hopefully it can be cleaned up good enough to reuse after a balance ......................compressor end all OK .

Something I just remembered .................on FM-1 when I first put her together , I felt there was a similar thing happening with flames coming back from the turbine wheel thru the ball bearings that were fed air from near the inner wall of the FT , I ended up fitting "snorkels " from the diffuser outlets to feed the shaft tunnel the highest pressure air I could , it did fix the "reflux" problem ..............mmmmm , might be whats happening now .

All food for thought :-)

Cheers
John

[racket]

Hi Ernie

LOL..... even the relatively thick 316 stainless NGV wall is burnt with some melting at the thinner tip rollover , the flametube was made from 800 series alloy , 30% nickel , 20% chrome ...goodshitium , the best I could source her in Oz ..................there was some serious flame direction problem for sure , the funny part was there wasn't any indication of problems looking up the jetpipe , combustion appeared OK with a "coolish" TOT of <600 deg C .

At least the compressor end survived without any damage , and the brass bush bearing appear OK , so something to be thankful for :-)

Cheers
John

[kellensinning]

Wow, I can't wait to see it fire up. I'm begining the initial design of my third engine, and i was wondering what are some good resources for designing an annular combustion chamber?

[racket]

Hi

LOL.....Pinch someone else's design and scale to suit :-)

My mate Smithy gave me a JetJoe 14 pounder flametube , I simply scaled up by 6 times as my TV94 comp has an inducer 6 times bigger than the Jet Joe's comp wheel .

Have you read Thomas Kamps book , if you haven't, then its a MUST READ , available from Traplet Publications shop.traplet.com/product.aspx?c=183 or sometimes on Ebay

Cheers
John

[jettoymaker]

Tried one...

Attachments:

[racket]

Hi Andrew

Lookin OK :-)

Cheers
John

[jettoymaker]

Thanks John ;D

[racket]

Hi Guys

Started reassembling the 10/98 today , flametube inner wall and inner rear wall replaced , new shaft tunnel heat shield made , NGV required a lot of rework as the severe overheating in one spot on the forward wall has distorted the assembly , new turbine wheel/shaft fitted to original compressor wheel and rebalanced, ......thanks Smithy:-)
and air deflectors fitted to diffuser outlets to direct half of the air radially down the front of the flametube and hopefully to the centre walls of the flametube

Impingement porting and plumbing fitted to comp front cover to possibly replace the electric starter , we'll see how things progress.

Should have the engine back together tomorrow if all goes well :-)

Cheers
John

[Richard OConnell]

Awesome! Looking forward to seeing more in this project

[racket]

Hi Richard

She's back in the test stand and I did an impingement spoolup test using 110psi air , it was useless , even needed a finger flick to get things spinning and then only ~1,500 rpm attained before air pressure started to fall along with rpm untill after ~20 seconds and at ~50 psi air pressure, the rotor stopped spinning.

Will hard line the oxy bottle to her to see what 2,000 psi will do .

Have also added a small 12V air comp to supply "scavanging" air to the area near the turb piston ring seal to help move the lube out of the shaft tunnel and stop it backing up and being forced out of the seal when the engine isn't running and theres no gas pressure on the wheel side of the seal .

Cheers
John

[racket]

Hi Guys

Bit of an update ..............fired her up yesterday , took her to ~67,000 rpm or 102% , tip speed ~1630 ft/sec , 3.4 PR , TOT of ~650 deg C , and as can be seen from the attached pic , the flametube survived OK with minimal heat colouration and no "burning" .

There is no heat soakback marks on the turbine shaft so the bleedair cooling to the turbine wheel hub area must be working now that the diffuser deflectors are forcing air to the shaft tunnel area .

Hopefully problems solved

Cheers
John

[racket]

Oops, attached pic

Attachments:

[pitciblackscotland]

Hi John,
Nice one, fingers cross for your next test run.

Mark...