Sunday, May 13, 2007

Testing 4/28

I'ts been 4 weeks since I last offered an update. We have been testing every 2 weeks, two weeks ago we went out to test with the goal of improving our ignition reliability and doing some throttle testing.

After reviewing the data from our earlier test series we learned that the fuel and LOX pressures were not coming up evenly to the commanded start position. The end result is that we tried to start at idle and then powered up to full throttle. We probably did this before the chamber was 100% lit causing harder starts. So we modified the software to change this sequence and went out to try again. The only physical change to the motor was a change from bolted to snap ring closures on the motor.

We tried to start the motor 4 times with only one successful light. After the first two failures to light we changed the software back to its origional condition and tried a third time, still no light.
So some diagnostics showed that the igniter fuel solenoid was dead. We replaced that and tried a fourth time. We did not switch the old software back to the new so for the forth attempt we successfully lit the motor but it started a bit hard. At this point we were suffering for the 3 failed attempts as we were running low on presurant gas. The video camera had also been running for more than an hour and it gave up the ghost so we got no video of the 4th run. The 4th run was a 30 second throttle test.

As we had been messing with the igniter connections diagnosing the no-light issues the igniter plumbing connection at the fuel solinoid was loose so we got chamber gas flow backwards into the igniter at about 20 seconds into the run the fuel solenoid decided it had had enough of hot gases leaking at it and let a burst of fuel into the aluminum line between the chamber and igniter. The mixture was just right to detonate in the line. So we have a small bulge/hole in the fuel line between the igniter and the fuel solenoid. At or near the same time the chamber pressure transducer disassembled it self. We did not notice any of this from the block house the only thing we knew is that the chamber pressure went to zero. The motor continued to run
and did its throttle steps for another 10 seconds or so. This chain of events is pure speculation based solely on the visual state after the run and the data we collected.

When we returned home and disassembled the motor we also determined that the injector plate was bent.

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