Again only tangentially related, but anyone happen to have seen the
critical diameter of mixed LOX/Methane? I still think it's insane to have
it in a tank as a monopropellant, but mixing it and injecting it into a
thrust chamber through porous sintered metal or laser drilled micro holes
could give interesting results if it doesn't explode.
You only need momentum out of the injector for mixing, and this would be
premixed. It's also the highest performance miscible propellant combo, as
far as I know. Should be able to run a fairly short L*.
On Wednesday, December 2, 2015, <snyder@xxxxxxxxxx> wrote:
This is particularly interesting to me, since I worked with they
guy(s) that started Firestar when they lived in Colorado and we
all worked for someone else.... on nitrous oxide monopropellants, mixed
monopropellants, bipropellants, (semi monopropellants :), breathing gas,
etc.
The first N2O mixed monopropellant test ran beautifully. I skipped the
celebrations at the strip club afterward...
The next (slightly hungover) day's test promptly exploded, as did
just about every test after that. Yep, flame arrestors, crossed
feed lines, smaller injectors holes. etc. Only one test may have
not back propagated into the main tank. It appeared to be a Powder
Filled Injector, (Zirconium) which ran at pretty low thrust.
Zirconium had shown some slight catalytic action on pure nitrous
in previous tests. The last thing we were talking about was some
chemical software that would tell us how a stable mix could be
made, while still making the N2O decomposition easier, and
possibly adding a little ISP. Buying (but not stealing) software at that
employer was really frowned upon, so it never went any further.
At the time, I assumed that is what Firestar was going to do.
I don't remember all the fuels we tried. Ethanol, Methanol, Propane,
Ethane, Propylene, etc. I suppose I could look it up. I don't believe
acetylene was ever tried. What 15psi autodetonation ? We were not that
crazy.
I know there was some talk of lawsuits (when a lawyer is on retainer, there
is always talk !) about intellectual property rights and a ridiculous
no-compete agreement. But I don't think Firestar had deep enough pockets
to make it worth while. But a lot of hard feelings, and some lawyer money
was generated.
There was always talk (and a little grant money) about N2O for use on
MMUs and ISS, but it never really seemed like a good idea with the
NOX productions. The hazards of premixed bipropellants made that
a dead end real quick. I was surprised that Firestar had any traction
with ISS use for any time at all.
The below description is a little surprising, since helium heads over
liquid N2O always seemed to reduce the explosive concerns. The
gas we could decompose (exothermically!) and therefor could have flashback
but the liquid could propagate the shock. Always fun to see 5000 Psi
1/4" tube laid out flat or fragmented. Just keep painting over the
shrapnel dings in the concrete test cell ....
Thanks for sharing,
-Gar
mix
Date: Tue, 1 Dec 2015 12:21:03 -0600
Subject: [AR] Re: ALASA cancelled because...
From: Ken Doyle <rocketken@xxxxxxxxx <javascript:;>>
That was me on Facebook mentioning that some success with Nitrous/Fuel
was had in the gaseous phase.kept
I worked at Firestar in Mojave for 3 years, leaving in very early 2012.
I'm pretty sure my NDA obligations have expired, and that Firestar is
defunct now.
The fundamental problem with use of a pre-mixed oxidizer/fuel in a rocket
motor is of course the issue of flashback, or a detonation wave traveling
upstream from the burning rocket motor to the tank holding the mix. We
did
have success in developing Flashback Arrestors for the gaseous phase.
Those detonations usually didn't explode the SS tubing on the way to the
Arrestor, and diverting the detonation wave and bursting relief parts
away the big kabooms.smaller
I setup and ran the tests of the arrestors, and the rocket motor tests.
For actual practical use in a flight motor, the higher density and
plumbing sizes that come with liquid-phase operation were going to bethat
necessary. The ever-optomistic CEO/Chief Scientist/Pitchman believed
the liquid phase of the mixes would be more stable and easier to arrestDrop
flashback than the gaseous phase. That hope proved to not be the case at
all.
Although they may have made some progress after I left the company; while
I
was there, we were never able to arrest flashback in the liquid phase.
We did most of the work with Nitrous Oxide mixed with Ethylene or
Acetylene. We did a series of 14 meter Drop Tests of the mixes, with the
Nitrous/Ethylene being much less prone to kerbleweys than the
Nitrous/Acetylene mixes. Although some attempt at subterfuge was made to
make it appear that we had a secret ingredient to help with stability, no
ingredients other than Nitrous Oxide and the Fuel were actually used.
With the Nitrous/Acetylene stoichiometric ratio mix tested, the first
Test passed, but the second failed violently. The evil mix had atendency
to explode at unexpected times; that is, in conditions less severe thanit
had previously passed through. For instance, I did a couple of slowto
heating tests which failed to explode at up to about 80C. Then, a test
where it exploded at only 50C. The difference in the tests was that the
50C explosion happened on a windy day, with some slight agitation due to
the wind moving the test apparatus.
Although the Nitrous/Ethylene mixes could pass some of the basic handling
safety tests, the arresting of flashback detonation waves in the liquid
phase was never solved while I was there.
In spite of highly negative handling safety experience with the
Nitrous/Acetylene mixes, a push persisted to make the stuff work, due to
the higher Isp number possible.
I was also chided about appearing to be afraid of the stuff, that my
cautious handling demeanor went against the company PR that it was safe
handle...hardware.
To sum up my opinion after working with Nitrous / Fuel monopropellant
blends for 3 years;
1. They are too dangerous to be anywhere near humans or valuable
2. The single tube/tank plumbing potential benefit is overcome by the
impracticality and weight of feasible flashback arresting notions.
Use of Nitrous and a reasonable fuel such as Ethylene, as a bi-prop, is
worth exploring.
It is conceivable that progress was made after I left Firestar, but none
of
my sources ever indicated such.
It is also conceivable that the ALASA / Boeing work with Nitrous /
Acetylene had no influence from the Firestar work, but I doubt that.
Ken Doyle