11/127 manned flight engine.

[racket]

Hi Guys

Well , I didn't escape yesterdays testrun without some damage :-(

One of the stainless NGV vanes failed , burnt out , the resulting bits then chewed the corner off the wheel's inducer , all blades identically, I'll set the wheel up in the lathe and grind the damaged corner to a reasonable shape to maintain balance and appearances.

It was a rather odd thing to happen , normally this sort of failure sees metal bits damaging the thermocouples , but all 4 of them are in perfect condition .

Seeing as how the wheel doesn't have the appearance of being cooked , and combined with the very high tip speeds of ~1660 ft/sec , one would imaging the wheel tips being thrown off if temps were excessive .............LOL, they were high though :-(

As theres a large amount of swirl within the flametube , produced by the 18 primary air tubes , one would imagine there'd be less chance of a hot streak .

I'll take some pics tomorrow when I finish pulling the engine apart .

My first attempts at starting the engine yesterday ended in failure , but after letting the batteries build up some voltage the second attempt went off OK , on packing up after the test whilst securing the starter motor to prevent it bouncing around on the trip home , the earth cable slipped out of it fitting where I'd soldered it in place .............sorta explained why I had problems getting the RPM up , might have been giving troubles for years.

I think my mods to the IGV angles and NGV throats are about right , fuel pressure at max power had the needle off the gauge , normally ~95 psi , this time >110 psi , she was working hard :-)

Cheers
John

[andym]

 Am sure you will have it back together in no time

[racket]

Hi Andy

I hope so :-)

Cheers
John

[finiteparts]

John, I wonder if perhaps you had a blade resonance and that is why the blade corners were broke off? Shock impingement on the blades is like hitting each blade with a small hammer with a count that is equal to the NGVs passages, each revolution. HCF cycles accumulate quickly. Especially since you are saying it didn't look cooked. Usually a chunk from upstream cause damage on a few blades, not all of them. Strange...

Do you have any pictures?

[racket]

Hi Chris

A few pics







Rather strange as the flametube inner rear wall where the gases go over into the NGV look OK , normally with a hot streak theres damage to the thin sheeting .

Its as though theres been an oxy torch on that vane , which has discharged "particles" against the wheel inducer and "slowly" eaten it away .

I might need to look at the possibility of an "air jet" from one of the holes between the evap tubes in the rear wall of the NGV supplying the "oxy" that cut the vane away .

I'll clean things up and "have a think"

Cheers
John

[racket]

And a couple more from "underneath"





Cheers
John

[madpatty]

Jun 26, 2024 21:13:10 GMT -5 racket said:

And a couple more from "underneath"





Cheers
John

I have seen this before 😟. That splitting of NGV at the halfway mark. Mine was over fuelling at lower RPMs though. But irrespective of that it was higher TETs that melted the vanes. Now it’s only a matter of which vane goes first and the. The chain reaction usually starts afterwards.

[racket]

Hi Patty

Lucky its was only one vane .

This is our last turbine wheel so I've got to keep it going .

Cheers
John

[slittlewing]

Hi John

It looks like it’s just melted from too high exhaust gas temp. The outer sections that remain will have been at lower temp than the middle due to their ability to conduct heat to the NGV walls. Unfortunately the other vanes don’t look too far off 😕 or at least have evidence of some surface melting.

The 870TOT during high PR tests is too high, especially given heat soak at 800 beforehand. Maybe even the 4 bar 800 TOT itself is too high to sustain without damage.

Cheers

Scott

[enginewhisperer]

maybe fuel collecting in the wake behind the evaporator tube and burning against the vane?

[finiteparts]

I see what you were saying...does look like a hot streak that locally heated the rotor blades, softening the material till you reached a local stress rupture.

How do the leading edges of the other vanes look? Just a theory, but maybe you had a deformation on that vane that increased its heat transfer that initiated the damage. Oxidation at high temps can occur quickly (i.e. acetylene torch when you give it high levels of O2), so even something small may have lit it off. If the NGV leading edges are getting oxidized, they might be getting close to failure. Also, do you see any LE cracks?

The local air jet theory is a good idea to check for also. Will be curious to see what you find there.

There are some weird looking ripple marks on the damaged ngv in that photo.
I wonder what that is?

Good luck,

Chris

[jetric]

Hi John,
I don't understand your logic in using stainless steel in one of the hottest parts of the engine especially with the 870oC plus EGT that your pushing the engine too, surely it would of been more logical to use inco for the NGV vanes. I think that there has been that many changes with this engine that you have lost your way with all the mods as you have done all the calculations for Andy Morris's engine and that works fine.

[finiteparts]

Have you back calculated a turbine inlet temp to meet your peak power condition?

I would be curious what inlet temperature you may have experienced.

Also, is there any upstream blockage that may have caused a wake? If so it may cause a local rich zone due to a lower than expected air flow to a section of the combustor. Stuff in the diffuser can cause wakes that persist into the combustor dilution feed holes, etc..

Any non-symmetric features on the liner due to heat damage or distortion?

Just throwing out ideas. Hope you find the smoking gun, so you can fix it. You're so close and it was really stretching it's legs, so to speak.

[racket]

Hi Richard

I generally use Inco , but its not so easy to source here in Australia , even more so since Covid disruption , hence my stainless use this last rebuild of the NGV .

Yep , I lost my way with the engine because of the new compressor wheel , the original compressor wheel/s worked OK with the turbine wheel size I have, but they were incapable of coping with any sort of decent compression ratio without stretching their bores .

The new wheel with its very high inducer angle simply wants to bite off more air than the turb can chew , this has created all sorts of problems , my early comp wheel was off a normal diesel engine turbo , this one is a racing tractor pulling wheel with unknown design requirements that was probably meant for 80+psi of boost , no matter what I try , I can't prevent the whole engine and test stand shaking when the engine is running.

Andys engine uses a comp with 10 degrees less inducer tip angle , its "normal" , so behaves as expected .

Ideally I need a much larger turbine wheel, but that then creates tip speed problems for the wheel , currently my comp tip speed is up around 1950 ft/sec with turb at ~1660 ft/sec , but another option is a larger flow wheel at lower pressure ratios from the comp , but finding an available turb wheel could be a challenge , I have contemplated a third stage Allison C20 wheel with tip laby seal removed , but its RPM is limited :-(

It seems a shame to have a beautiful comp wheel that can't be allowed to do what it wants to do , it has some unique characteristics that need exploring , like an inducer that has angles that will bite off more air than its throat can swallow without there being shock wave compression as with fan engine blades ........... I've got a highly strung race horse kicking the crap out of its stall wanting to run , but I'm not able to accommodate it :-(

Frustrating business R and D.

Cheers
John

[racket]

Hi Chris

The flametube looks great , exactly the same as it has after the last several testruns , the fitting of air deflectors at the diffuser outlets and the swirl producing Primary air tubes has worked wonders , previously when theres been overtemp problems the flametube has suffered .

Temperatures were high but there was very little restriction downstream , the exducer throats are ~10.2 sq ins , the jet nozzle was ~17 sq ins , the jetpipe is 130 mm , the jet nozzle 127 mm( 45 mm central turb hub fairing) so only 3 mm of nozzle .

The damage to other vanes is from the bits getting thrown back and forth , one of the problems with radial wheels , the NGV suffers more than an axial setup .

Cheers
John