April 29 and May 3, 2003 Meeting Notes
We did a good set of experiments with different fuel / catalyst
mixtures this week, working towards possible bipropellant options with 50%
peroxide while we are waiting for more 90%.
A few things are looking good on the 90% front, but we are still
pursuing backup plans.
We did another experiment with the mixed-monopropellant
scheme, dissolving 8% by mass glycerine with 50% concentration peroxide, in
hopes that permanganate catalyst solution would auto-ignite the mix based on
the energetic permanganate / glycerin reaction. No luck. We have seen a
few references to these types of mixed monopropellants in use long ago for
torpedo drives, but we havent been able to get them to do anything. We havent been too disappointed, because
mixing up large quantities of an oxidizer / fuel mixture would be a bit nervy. With high concentration peroxide, that is a
sure detonation risk, but 50% water is supposed to desensitize it sufficiently
for operational use.
The only thing we have seen auto-ignite with 50% peroxide is
red phosphorous, which is generally nasty stuff that probably wouldnt dissolve
in anything anyway (and we dont intend to find out).
We have heard from a couple places that 50% concentration
peroxide burning with fuels is not self-sustaining without a catalyst of some
kind, and our silver screen catalyst packs werent even close to decomposing
all the 50% peroxide we tried to flow through it, so the three possible options
50% peroxide mixed with a fuel, plus an aqueous catalyst
50% peroxide, plus a fuel / catalyst mixture
50% peroxide, plus a fuel, plus an aqueous catalyst
A triprop with only a 160-180 Isp would be rather depressing
(and adding more water wouldnt be helpful), and the peroxide / fuel mixtures
are scary, so we would really prefer to find a good fuel / catalyst mixture.
Our previous tests with dissolved catalysts in fuels had
used manganese acetate dissolved in ethanol with the addition of some epoxy
hardener to act as a promoter. I dont
care for the three-part mix, so we tried dissolving potassium permanganate in
several different fuels:
The only one that lets any dissolve is acetone, which holds
about as much in solution as water does.
It is hard to tell how much is in solution with the dark purple color,
so we ran the solution through filter paper to make sure we didnt have any
suspended solids. We also have some
sodium permanganate on the way to try later, but the acetone / permanganate
mixture does seem to be stable and workable. There is still a notable concern with leaving deposits in the
plumbing when the acetone evaporates away, and it does generally make a mess.
One other experiment of note: if you drop a few grains of potassium permanganate into a larger
quantity of peroxide, it will catalyze the peroxide for a while, then
completely vanish. This consumption of
the catalyst probably bodes very poorly for the longevity of ceramic catalysts
with baked-on permanganates that are often proposed for 98% peroxide use.
The more we work with other propulsion options, the more we appreciate
the benefits of 90% peroxide / kerosene with catalyst pack based auto-ignition.
We finished the boring and tapping of the distribution
manifolds for our big cooling jacketed aluminum motor.chamber. This was built for a 1000 lbf regeneratively
cooled 90% peroxide / kerosene engine, but we figured we might as well use it
for our 50% peroxide engine tests. The
cooling jacket is more restrictive than it probably should be: there is a 0.010
gap between the inner and outer walls (4.5 diameter), which gives 0.143 square
inches, which is only mildly less than the feed line, but all the wetted
surface area adds a lot more drag. We
will probably turn the inner section down another 0.010 or so in the future,
but we are just using it connected to a water hose for now, and the 50% engine
wont make all that much heat, so it isnt a priority.
I added data collection options to my program that sequences
all the ignitor valves and spark plugs, so we have a nice little test bed. I also added key commands to manually
actuate each of the controlled solenoids for testing. I installed a pressure transducer on the engine with a standoff
line and a snubber, which should keep it from cooking.
We have previously noticed that it isnt that hard to get a
fairly big bang when the XCOR torch igniter lights, if the chamber has any
residual fuel vapor in it. Working with
volatile acetone based fuels today made it a lot worse, so we finally got tired
of the bangs and installed a fairly high flow nitrogen purge. Yet another valve to control.
The igniter was delivered from XCOR with 24VDC solenoids,
because they typically work with airplane electrical systems, but we will be
swapping the coils for 12VDC to make our lives easier. The solenoid company http://www.snap-tite.com/divisions/sv/index.html
has a wide range of solenoid offerings, which we may start using some of in the
future. The NOS nitrous solenoids that
we typically use have a pretty big price markup, and they are overdriving the
coils quite a bit to make them operate at higher pressure / flow rates, which
makes them burn out if left on too long.
We had hit-or-miss results with the testing. Sometimes we got it to light, and sometimes
we just had a gush of liquid out the bottom of the engine (we are definitely doing
all this testing vertically, to avoid any chance of pooled propellants in the
chamber). We believe that we need to
get the torch igniter operating at a higher pressure for a longer torch flame,
but I need to find a high-pressure oxygen regulator to do that.
We also should measure the actual flow rate through our two feed
systems. The spray nozzles are sized to
give the correct ratio, but the solenoids and plumbing may be skewing the