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"
) 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