having some working understanding of a jet engine, i came across an odd looking piece of kit out in the rain (really in the rain!). Being the way i am questions needed to be asked. Hell "jet engine in the rain" what is going on ?
A little enquiry and some negotiations saw the thing in the back of my van, obviously that is where it should have been kept :)
While poking around i could not leave the control box unopened so out it comes for a quick check. The rain seems not to have got in so lucky there, the Processor block (seems to be an ATmega12816Au) very similar to my Arduino APU project
After all the checks and completing a new wiring diagram, its time to begin the initial tests. I need compressed air at 100Psi on tap to spin up the core, As its a test i need to know the pumps will run, to be on the safe side i will disconnect the fuel pump so we do not have the neighbours out.
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Initial results look good the engine wound up to around 18,000rpm and then detected a false start (due to no fuel), although it did seem a little unusual, the fuel and oil pumps are tied together so one on both on. Fuel is not required until 17,000 rpm at this point the pumps are activated, so no oil is pumped through to the bearings until 17,000 is reached, it is only a short period before the pumps activate but multiple false starts could begin to starve the bearings of oil.
Displays and gauges all seem to function so another bonus.
A few more test runs and things are looking pretty good, a check of the ignition system proved the sparking plug works too (Somewhat diddy).
I still haven't found any reason for allowing the engine to be discarded but im not finished yet, time for a clean and to add some fuel.
After the test run (and a few more for good measure) its apparent it wont run for long. I does not reach the minimum RPM within its set time. during the visual inspection nothing seems wrong, rotor revolves ok, fuel and oil are fine, it actually starts so electronics are good. This thing is going to have to come apart for further investigation.
Hmm it didn't take long to identify the issue.
Once the front generator (nose cover) was removed i can get better access to the air compressor. Give it a spin and it all starts to make sense.
Hang on, what's this..
As the cover was removed the bearing race shield has moved and released some balls, now that should not happen, something is a miss !
Here is the bearing race, you can just see where the balls have begun to pick up on the surface, On the up side, I may have just saved the whole thing from disintegrating, If the bearings had completely given up then it would be game over.
O dear, some one forgot to tighten some bolts or missed the retaining wire. Some of the cap head bolts on the combustion side have sheared off but were not able to make there way out of the engine. Rumble Rumble, as they churned around inside which now resemble ball bearings, not so good. Some damage to surfaces but nothing major (in a jet engine!) they can be cleaned, new bolts and reassembly should be ok.
Well i have the spindle out and some new bearings, Im working on a side project to build a dynamic balancing machine, as i have 2 engines now that could do with a tune up. Once that's done "ill be back" and start re-assembly.
With the spindle out it looks like a cast one piece design, there are a few marks on the shaft probably down to vibration as the shaft spins up to 90,000 rpm and has had a bearing failure to boot
New bearings are a matched precision high speed pair (£ 250.00) and were a simple replacement. Some vibration damage was evident on the bearing housings but as no other parts are available, in they go.
Some of the bolts has suffered from fatigue failure and needed replacement, it seems Americans still use imperial threads as the new ones are witworth threads. New bolts didn't have the wire lock holes so very carefully new holes were drilled into the stainless steel heads using a 1mm drill.
Retaining plates locked into place and wire tied
This is the spindle back in place, spinning the core is now smooth and noise free, absolute cleanliness needed as any partials could cause wear on the balls and we will be back to square one.
Front image with the inlet fitted
High pressure fuel lines fitted, temperature sensors and thronal assembly. A good clean up and ready for a trial start.
Oh Dear !
Upon starting the engine something has not gone to plan. The system monitors the spindle rpm before fuel and oil pumps are started (around 17,000 rpm), once reached the fuel and oil are injected. All good so far except for the oil transfer from the outer union to the inner cavity. The O-rings had been trapped on assembly and allowed oil to transfer into the air compressor cavity.
Ever heard of a old diesel engine self consume its own internal oil and become uncontrollable to the point of dramatically expiring ? Similar issue but this is a jet engine, Something was wrong so I hit the stop button and it keeps going ! the only way to stop it is to cut the incoming air supply to stop the combustion. Remember the compressor is still running at around 40 to 50,000 rpm, 1st I had to grab something large enough to stop the air entering the compressor intake. 2nd deal with the fire. Hot oil had accumulated in the exit exhaust chamber and was on fire. Similar to a chip pan fire so now stop air getting in the rear before the case temperature caused irreversible damage.
Although it might look great to see me panicking to get control of the issue, I was not recording the event.
The O-ring problem took some solving, there are no seals to prevent oil passing between the shaft and the compressor/exhaust cavities. Each static test of oil pressure allowed oil to exit into the engine cavities, it seems the bearing oil pressure is balanced against the internal running pressure which stops oil leaking past the end plates. Once the O-Ring problem was solved and a good clean another test run is in order.
Success !
Re-Cap
Oil pressure O-rings fixed'
Burnt oil removed
Ignition chamber emptied and cleaned
Quick examination for temperature damage
Additional fire blanket on hand
TBC...
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