"A monopropellant is a liquid which contains in itself both the fuel and
the oxidizer…. But! Any intimate mixture of a fuel and an oxidizer is a
potential explosive, and a molecule with one reducing (fuel) end and one
oxidizing end, separated by a pair of firmly crossed fingers, is an
invitation to disaster."
-John Clark, Ignition!
On 12/1/2015 1:48 PM, George Herbert wrote:
While I generally agree with Henry on monoprops, there are materials like OTTO
fuel, TATB, Fox-7, and Class 1.3 propellants where accidental mass detonation
is rare and energy density doesn't totally suck.
We need stabler monoprops.
George William Herbert
Sent from my iPhone
On Dec 1, 2015, at 1:29 PM, Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx> wrote:
I'm tempted to propose a rule: Any liquid monoprop energetic enough to have
high performance is vanishingly unlikely to be reliably stable under the
violent conditions involved in flow through practical rocket motor feed
plumbing.
On 12/1/2015 11:21 AM, Ken Doyle wrote:
That was me on Facebook mentioning that some success with Nitrous/Fuel
mix was had in the gaseous phase.
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 kept away the big kabooms.
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
smaller plumbing sizes that come with liquid-phase operation were going
to be necessary. The ever-optomistic CEO/Chief Scientist/Pitchman
believed that the liquid phase of the mixes would be more stable and
easier to arrest 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
Drop Test passed, but the second failed violently. The evil mix had a
tendency to explode at unexpected times; that is, in conditions less
severe than it had previously passed through. For instance, I did a
couple of slow 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
to handle...
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 hardware.
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