August 29, 2004 notes:
Matt was out of town all week, getting trained on and
picking up his new Cirrus SR20, so no photos this time.
We are still having chugging problems with the 7 engine at
full throttle. We have tried a great
many things that made no difference at all (still good data points), and a
couple things that made a difference, but still didnt fix it. We arent going to finish the new 12 engine
until we definitively fix this on the 7 engine. The worry is that the catalyst monoliths we have on hand are not
exactly the same as the ones that were in the known good engine
configurations. If we have to order
more, that would be a five week lead.
We do have another 12 monolith exactly like the one in the engine that
worked well, but again, I really want to get the 7 engine working properly
All the configurations we have tried:
Two 1 thick 900 cpsi monoliths with 1676 x 0.022 spreading
Two 1 thick 900 cpsi monoliths with 940 x 0.022 spreading
One 1 thick 900 cpsi monoliths with 940 x 0.022 spreading
One 1 thick 900 cpsi monoliths with 584 x 0.022 spreading
50% open area perf plate under the cold support plate and
25% open area plate under the cold support plate.
Choke plate with only 8 x 0.5 holes, underneath spark plug.
Hot pack with single layer of 1000 grams, compressed to 4000
Hot pack with two layers of 500 grams each, compressed to
3300 psi gauge
Hot pack with three layers of 250 grams each, uncompressed
Optional 10 extra 20 mesh screens below monolith.
Domed or flat top above spreading plate.
More or less volume above spreading plate.
With or without support pegs between the spreading plate and
0.25 Cavitating venturi
0.3 Cavitating venturi
I gathered all of our notes and data into one place and
reviewed them again tonight.
The initial runs with two monoliths were stable at much
higher thrust levels that all the configurations with only a single monolith.
Something I hadnt noticed before was that the double monolith
runs were also over 100C hotter than the later runs. That might have something to do with the fact that it ran at a
higher pressure, but it does look like I had runs that were at stable
temperatures both ways.
The lighter, segmented, and uncompressed hot pack did have
about 10% less pressure drop than the single layer compressed pack, and it was
able to run slightly higher thrust without instability.
These support our theory that the pressure drop needs to be
higher through the cold pack than the hot pack, but we are having difficulty
getting more drop in the cold pack.
Adding ten screens underneath the monolith didnt give any measurable
increase in the pressure drop, rather to our surprise. Neither did adding a 25% open area perf
plate. With a good amount of the flow
from the cold pack still being liquid, the velocities must be quite low. The choke plate did increase the pressure
drop a lot, but it didnt move the stability point, probably because it was
below the spark plug, and the pressure drop needs to be before any combustion
The temperature result does imply that the double thick
monolith is still catalyzing more peroxide than the single monolith, which should
make the pressure drop a lot greater than simply doubling the drop of a single
Our next test will be rebuilding the top with a double
monolith and adding even more screens below it, which should push the top
pressure drop higher than the hot pack.
We might even try three monoliths, with the thinking that we might as
well put active elements in instead of inert screens, but we sometimes have
difficulty getting the flameholder started on engines with very strong cold
packs, because the methanol starts catalytically breaking down before it gets a
chance to burn.
In other work, Russ and Tommy have been working on custom
board layouts for our new electronics systems.
The new boards will be much smaller than our old electronics systems,
and wont have any of the on-board cabling we used to have. There will be short ribbon cables coming
down from the PC104 boards, but that will be about it.