Newsgroups: sci.space.tech
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Monopropellants
Date: Tue, 21 Apr 1998 18:20:12 GMT

In article <3538E49E.2ED10B0D@burningbridges.com>,
Hiram Berry  <burningb@burningbridges.com> wrote:
>...I have a question:  has anyone
>tried using tetramethylammonium nitrate, or some other quartenary alkyl
>ammonium nitrate, dissolved in N2O4 or possibly RFNA?

Yes.  See chapter 11 of John Clark's classic "Ignition!".  The alkyl
ammonium nitrates typically aren't very soluble in N2O4, but they dissolve
just fine in WFNA (pure HNO3; nobody wants to work with RFNA when WFNA
will do).  Stability varies with structure but is sometimes quite good;
the quaternaries are generally the best and the tetramethyl one is
particularly durable.

Unfortunately, all energetic monopropellants will explode if hit hard
enough.  Clark's group eventually found some quaternaries that were even
less sensitive than tetramethyl, but an attempt to test a 10,000lb engine
using one of them failed most spectacularly when ignition problems caused
a chamber explosion and fragments from the injector smashed into the tank
and detonated 200lb of energetic monopropellant.  The test cell -- with
concrete walls 2ft thick -- was completely demolished.

Low-energy monopropellants like H2O2 and N2H4 are quite workable, but
after a lot of money was put into high-energy ones, the conclusion was
that high energy and adequate stability are fundamentally incompatible.
A few of the most stable quaternary alkyl ammonium nitrates did come
close to being usable, but not close enough.
--
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         | henry@zoo.toronto.edu

From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: mix oxidizer and fuel together
Date: Sat, 4 Apr 1998 05:27:27 GMT

In article <1998040322375701.RAA04628@ladder01.news.aol.com>,
Guff12345 <guff12345@aol.com> wrote:
>Is it possible to mix a liquid oxidizer and liquid fuel together in one tank
>and then pump that mix out and ignite it to provide rocket propulsion?

It is theoretically possible.  However, when this is tried the outcome is
almost always one of two possibilities.  The good outcome is that the two
simply won't mix in any satisfactory way; for example, kerosene and H2O2
are immiscible.  The other usual outcome is that the mixture is found to
be a powerful and hideously sensitive explosive; for example, LOX/methane
mixes just fine but merely shining a light on it can make it explode.

>Explosions might be a problem however with no heat source to ignite the mix it
>should be pretty stable.

Unfortunately, only the more stable explosives need something as blatant
as a heat source to set them off.  The really nasty ones -- and almost any
oxidizer/fuel mixture energetic enough to be interesting for rockets
qualifies -- can be set off by even trivial disturbances, such as a valve
opening.

>Ensuring good mixing throughout tank (so always stay in right combustion
>proportions) could be a big problem...  Are there any two propellants (oxidizer
>and fuel) that have the same density?

Not an issue if the two liquids are miscible.  Alcohol and water do not
have the same density, but alcohol/water mixtures have no tendency to
spontaneously separate, and once you get the mixture uniform it stays
that way.

>Since most petroleum fuels are soups of
>numerous different molecule lengths would these fuels tend to separate by
>density at high G levels (I don't think so)?

Not at any ordinary acceleration.  Ultracentrifuges can separate miscible
liquids that way (for that matter, they can separate salt out of water),
but under most any less severe conditions, the agitation caused by normal
molecular motion keeps such mixtures mixed.

>Might the two propellants behave too mechanically different in the pumping
>machinary (non-even flow, cavitation, etc.)?  If both are kept liquid would
>different boiling temps cause any problem at all?

When you start heating such a mixture life can get complicated, because
generally one component will concentrate in the liquid and the other in
the vapor.  (Again, alcohol/water is a good example, with most of the
alcohol boiling off and most of the water staying behind.)  This can mess
up attempts to avoid particularly explosive mixture ratios.  The guys who
were trying to use liquid ozone dissolved in LOX as an oxidizer found out
the hard way that they had to blow their plumbing clean with inert gas
after every firing; leaving any of the mixture in the plumbing as it
warmed up guaranteed ozone explosions, because the LOX boiled off first.

>Well, could it work?

No.  It's been tried.  Repeatedly.  The luckier experimenters gave up on
it before anyone was killed.
--
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         | henry@zoo.toronto.edu