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Innards Of A Jet Engine  
User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Posted (10 years 2 months 3 weeks 8 hours ago) and read 32767 times:

Hello, friends,

Today I´ve done a boroscope inspection of a PW 2040 engine (again!) and I´d like to post some pictures of things you people (even you glamour boys and girls in the "front office"  Smile/happy/getting dizzy ) probably have never seen before (except mechanics and licenced engineers of course).
The pictures were taken with a 6mm flexible boroscope. A boroscope is a close relative of a medical endoscope. It consists primarely of a long thin flexible probe with a fiber optic inside. The tip can be moved by remote control and it contains a strong light source. On this (digital) boroscope the pictures can be seen on a lcd screen and saved using a floppy disk. The idea is to be able to inspect the innards of an engine without having to dismantle it. There are so called boro plugs, holes closed with a screwed in plug, al over the engine in critical places, permitting the insertion of the probe. What I did today was a routine inspection of a healthy, but not too new PW 2040 engine of a B757. Enjoy!

Starting at the front here is a picture of the 10th stage High Pressure Compressor. You can recongnise the vanes and the rotating blades. I had to check the outside brazed joint of the vanes for cracks. The round holes are openings where bleed air is taken out of the engine. The shiny spots on the vanes are not cracks, but some vaseline rubbed off, which I used to lubricate the probe.


The next one is a shot of the combustion chamber. This engine has an annular combustion chamber made up of loosely interlocked rings (to allow for thermal expansion). At the front end are the round injection nozzles. The nozzles close to the ignitor plugs are a bit soothy, but this is normal. Only part of the air is directly mixed with the fuel to allow a chemicaly combustible mix. Additional air is added through the holes in the combustion chamber liner to cool down the hot gases (the flame is almost 2000°c hot, too much for the turbine, the max EGT on startup, measured behind the last turbine stage is 425°C).


Here is a close up of an injection nozzle, you can see the swirl vanes around the actual nozzle, which provide a vortex for good mixing of fuel and air.


Next is picture of the tip of an ignitor plug sticking into the combustor, there are two of them on each engine, each powered by a seperate system.


Now we see the rear end of the combustion chamber, where the hot gases enter the nozzle guide vanes to be dircted into the first stage of the High pressure turbine. This is the hottest and most highly stressed area of the engine. The nozzle guide vanes are cooled by "cold" (still around 400°C) bleed air being ducted through their inside. The air escapes through the multitude of small holes drilled into them and forms a protective film arounfd the vane. The vanes look a bit dirty due to residue from the combustion, and in some places the ceramic coating has flaked off a bit, but everything is within limits.


Between the vanes you can see the blades of the first stage HPT, which are not only exposed to an intense heat, but also to high centrigugal forces.
They are cooled in a similar way as the nozzle guide vanes. Here is a better picture of a blade:


Finaly we reach the second stage HPT, where the gases have cooled down quite a bit (they lost energy turning the first stage turbine). Everything is cleaner, but the blades (we look at the trailing edge) are still being cooled internaly (see the slits at the trailing edge). You can se the rub strip on the turbine casing, a soft material, which gets worn in by the turbine blades, so that the gap between the turbine and the casing will be as small as possible for efficiency reasons. The casing is also cooled from the outside with bleed air sprayed on it from a series of pipes with small holes drilled into them to shrink it controlled to keep this gap small, even under thermal expansion.


Finaly here is a selfpic taken with the boroscope:



I hope you enjoyed

Jan


25 replies: All unread, showing first 25:
 
User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 1, posted (10 years 2 months 3 weeks 8 hours ago) and read 32767 times:

Thanks a lot Jan for sharing these pictures with us. It's for posts like these I keep coming everyday to airliners.net  Big thumbs up

I have a question for you, what sort of things specifically were you looking for during the inspection? How does a damaged part look? Thanks again

-Alfredo
ps: Some pictures are not loading




EDIT: typos...

[Edited 2004-04-25 00:04:49]

User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 26
Reply 2, posted (10 years 2 months 3 weeks 8 hours ago) and read 32767 times:

Really amazing photos! Thanks for sharing...

Cheers,
QantasA332


User currently offlinePelican From Germany, joined Apr 2004, 2531 posts, RR: 8
Reply 3, posted (10 years 2 months 3 weeks 8 hours ago) and read 32767 times:

I have never seen something like this (off course). Very interesting!
Not the standard "what is water injection" thread - posted by unaware folks like me  Smile/happy/getting dizzy

BTW is it my notebook or why can't I see all pictures (I am eager to see them, too)


User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Reply 4, posted (10 years 2 months 3 weeks 8 hours ago) and read 32767 times:

Things I would look for on a general hot section inspection:
Cracks, burn marks, distorted or molten parts of the combustion chamber liners, which might point to a faulty injetion nozzle (when it doesn´t eject the fuel as a fine spray, to burn immidiately, but as a burning jet, which might strike some part and overheat it, on turbine blades and vanes sulphurisation, blueish or grey discolourisations, which can happen if the fuel contains too much sulphur. It will alloy itself with the metal and make it brittle. Shingled turbine blade shrouds (if the tip shrouds of the blades are not side by side, but overlapping), blade clashing (blades touching some nonmoving part of the engine), FOD, discoloured parts (which could signify an overheating).

There is also an AD out for a continued inspection of the 10th and 11th stage HPC stator vanes one PW2040 engines of certain serial numbers. The stator vanes of thse engines tended to develop cracks in the outer tiptrailing edge region, which caused some engines to "auto shut down" in flight with spectacular results (a vane breaking off and going downstream through the engine). This will continue until this engine goes back to the shop for overhaul and the offending stator segments will be exchanged for modified ones.

Jan


User currently offlineAloges From Germany, joined Jan 2006, 8669 posts, RR: 43
Reply 5, posted (10 years 2 months 3 weeks 7 hours ago) and read 32767 times:

I hope you don't mind if I repost Jan's text and add the two pics I managed to get working (hopefully):

"The next one is a shot of the combustion chamber. This engine has an annular combustion chamber made up of loosely interlocked rings (to allow for thermal expansion). At the front end are the round injection nozzles. The nozzles close to the ignitor plugs are a bit soothy, but this is normal. Only part of the air is directly mixed with the fuel to allow a chemicaly combustible mix. Additional air is added through the holes in the combustion chamber liner to cool down the hot gases (the flame is almost 2000°c hot, too much for the turbine, the max EGT on startup, measured behind the last turbine stage is 425°C)."



"Finaly here is a selfpic taken with the boroscope:"



Jan, thanks a lot for this great insight (pun fully intended), RU list for you!  Big thumbs up

[Edited 2004-04-25 01:12:40]


Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineNoUFO From Germany, joined Apr 2001, 7941 posts, RR: 12
Reply 6, posted (10 years 2 months 3 weeks 7 hours ago) and read 32767 times:

Now that was great; thanks a lot!  Smile


I support the right to arm bears
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 7, posted (10 years 2 months 3 weeks 6 hours ago) and read 32767 times:

Nice photos! Always nice to see new stuff on a.net!

Staffan


User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Reply 8, posted (10 years 2 months 3 weeks 6 hours ago) and read 32767 times:

Thanks!

I had this problem with the pictures not loading quite often with posts with many pictures. I assume that the loading time takes so long that the connection times out.

Jan


User currently onlineKlaus From Germany, joined Jul 2001, 21388 posts, RR: 54
Reply 9, posted (10 years 2 months 3 weeks 6 hours ago) and read 32767 times:

Most excellent post, indeed!  Big thumbs up

Regarding the compressor / turbine disks: It seems the high pressure compressor shown above is a single piece; Is that correct? And how many stages have individually removable blades and how many are "solid" (if any)?

I´ve only read about single-part compressors/turbines in context with military engines, so I don´t know about commercial ones...

I guess cost would be the limiting factor (One damaged blade would ruin the entire disk).


MD11Engineer: I had this problem with the pictures not loading quite often with posts with many pictures. I assume that the loading time takes so long that the connection times out.

No, the URLs just got mixed up in your post; After manually cleaning them up (open picture in separate window, check URL), the pictures did indeed load (at least the two Aloges included above).


And I agree, any further insight is highly welcome!  Big thumbs up


User currently offlineUAL Bagsmasher From United States of America, joined Sep 1999, 2146 posts, RR: 10
Reply 10, posted (10 years 2 months 3 weeks 3 hours ago) and read 32767 times:

The thing I find interesting is that many of these parts look exactly the same as those on our PT-6's at school. Although they are obviously larger, and the PT-6 is annular reverse flow.

User currently offlineGoboeing From United States of America, joined Jun 2000, 2682 posts, RR: 14
Reply 11, posted (10 years 2 months 3 weeks 3 hours ago) and read 32767 times:

Very informative! Thank you!

Nick


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 12, posted (10 years 2 months 2 weeks 6 days 20 hours ago) and read 32767 times:

Good post!

Heh, seems a.net censored the pic of you at first... I would be offended! Big grin

Cheers,
Fred




I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineBuckfifty From Canada, joined Oct 2001, 1316 posts, RR: 20
Reply 13, posted (10 years 2 months 2 weeks 6 days 17 hours ago) and read 32767 times:

Awesome! Those are great Jan! Going to save them on my computer for prosperity (except for your picture, of course)  Big grin

User currently offlineAUAE From United States of America, joined Apr 2004, 296 posts, RR: 3
Reply 14, posted (10 years 2 months 2 weeks 6 days 16 hours ago) and read 32767 times:

Kluas,

It has been quite a while since I worked on PW2037's, but I don't remember any of the compressor disks being one piece. As far as I can remember, all the compressor blades are individual. Some turbine vanes come in pieces of three of four vanes together. Only thing I can think of that is one piece that is interesting is the compressor spool. The rotating disk that the compressor (stages ?? to ??) is made up of several disks, inertia welded together. It looks like a beer keg, sorta.  Smile

Jan,

The ablative material that blades rub away is rubber in the front section of the engine, but I believe in the picture it is ceramic type material. Is that correct? Ceramic ablatives in the tail section?

Regards,
Shawn



Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Reply 15, posted (10 years 2 months 2 weeks 6 days 8 hours ago) and read 32767 times:

First, I´ve got a small correction to make: The max start EGT is 485°C, not 425°C.

Klaus,
Concerning the picture of the 10th stage HPC vanes, what you see on the top are the trailing edges of the 10th stage vanes. They come in segments of 5 to 6 vanes. They are also the first non variable vanes of the HPC, all vanes of the HPC forward are variable, e.g. their angle of attack can be changed. On the bottom you see the 11th stage HPC rotor blades. They come single and are dovetailed into the compressor disk.There are 74 blades in the 11th stage. The blade is only 2.050 inches long, the last 17th stage blades are only 1.175 inches long (this is important for estimating the size of possible damage, one of the hardest things when doing boroscope inspections, is it still within limits?).

The turbine blades are also fir tree jointed into the turbine disk. Just for info, the 1st stage HPT blades are 2,32 inches long.

P.S. the rub strip in the turbine is made of some soft ceramic stuff (don´t ask me, all I´ve been doing is boroscopes, I never dismanteled a PW 2040)

Jan




User currently onlineKlaus From Germany, joined Jul 2001, 21388 posts, RR: 54
Reply 16, posted (10 years 2 months 2 weeks 6 days 8 hours ago) and read 32767 times:

Thank you both; In the picture above, the disk/blade joints just happen to be a little out of focus (as they´re probably not the most interesting aspect at this point) so I wasn´t sure.

User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Reply 17, posted (10 years 2 months 2 weeks 6 days 7 hours ago) and read 32767 times:

Klaus,

The boroscope optics have only a very limited field of focus, additionaly the digital camera on this one is always focusing on what is in the centre of the picture. Sometimes it realy annoys me, e.g. if I do an AD inspection of the 5th stage LPT blades for blade clashing (one some engines the 5th stage LPT stator segments moved aft and touched the rotor, one engine quit with a loud bang and a fireball, and the maintenance crew had to pick up a bucket full of turbine blades from the runway...), I use a very old simple 4 mm boroscope without a camera, I just have to peep through the optics.

Jan


User currently offlineLMP737 From , joined Dec 1969, posts, RR:
Reply 18, posted (10 years 2 months 2 weeks 6 days 6 hours ago) and read 32767 times:

Great pictures MD11Engineer! It's been awhile since I've done a boresope myself. Actually the last one I did was in the navy on a TF-30 checking for FOD damage on the N2. A couple months ago I did have the "honor" of re-installing the inspection plugs on a Trent 892 after inspection guys got done doing their part.

User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 19, posted (10 years 2 months 2 weeks 6 days 5 hours ago) and read 32767 times:

That was really cool! Thank you MD11Engineer




Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineToni_ From Cape Verde, joined Apr 2002, 93 posts, RR: 0
Reply 20, posted (10 years 2 months 2 weeks 5 days 15 hours ago) and read 32767 times:

Hallo Jan

During the period that I worked as mechanic I never had the chance to work with boroscopes. I remember at school we had photos in our study books too, but none were as detailed as these ones.
Neat!

Thanks again for sharing them
Danke  Smile

Toni


User currently offlineBrons2 From United States of America, joined Sep 2001, 3007 posts, RR: 4
Reply 21, posted (10 years 2 months 2 weeks 5 days 14 hours ago) and read 32722 times:

In my time I have disassembled quite a few land based reciprocal engines (auto, motorcycle, jet ski, mower) and the one thing that came to mind was, that turbine is much cleaner on the inside than any engine I have ever taken apart. With the notable exception of the injector nozzle, it looked pretty nasty compared to auto injectors that I have seen.

Also, the igniter was interesting, I was expecting something that looked more like a spark plug.



Firings, if well done, are good for employee morale.
User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Reply 22, posted (10 years 2 months 2 weeks 5 days 14 hours ago) and read 32695 times:

That ignitor head has a diametre of about 1/2 inch. The spark occurs between a recessed center electrode and the edge and has the shape of a ball. The voltages and currents used are lethal, this is why we always pull the ignition system C/Bs, disconnect the power input of the exciter box and wait for 10 minutes to let the capacitators discharge before we disconnect any of the high voltage leads.

The combustion in gas turbine engines is continous, because of this it can be much better regulated than a piston engine. Actualy only the two injection nozzles in the vicinity of the ignitor plugs are that dirty. The reason is that these injection nozzles allow a richer mix to improve starting.

Another thing about turbine engines is that it is rarely necessary to change oil. The oil in the tank after weeks of use looks just like the oil fresh out of a can. If it gets dark then there is something wrong with the engine, e.g. a bearing chamber seal is failing. Usualy we only top the oil level up to compensate for oil loss during operation.

Jan


User currently offlineOkie From United States of America, joined Jul 2003, 2969 posts, RR: 3
Reply 23, posted (10 years 2 months 2 weeks 5 days 1 hour ago) and read 32482 times:

Thanks for the informative picks MD11Engineer.
Is that some sort of insulation around outside ring of the mixer nozzle or just fuel residue?

he keeps getting richer
but can't get his picture
on the cover of the A net news
(I think that was a line in an old song)

Okie


User currently offlineMD11Engineer From Germany, joined Oct 2003, 13943 posts, RR: 63
Reply 24, posted (10 years 2 months 2 weeks 4 days 16 hours ago) and read 32376 times:

Yes, there is some ceramic coating on the outer ring of the injection nozzle. Actually the whole combustion chamber liner and the turbine blades and vanes are coated with different types of ceramics.

Jan


User currently offlineSinlock From United States of America, joined Dec 2000, 1637 posts, RR: 2
Reply 25, posted (10 years 2 months 2 weeks 4 days 14 hours ago) and read 32328 times:

MD11Engineer,


Top notch post. It's members like you that help keep up A.net's reputation.



Respected User



My Country can beat up your Country....
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