From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Propane/LOX
Date: Wed, 5 Jan 2000 20:37:32 GMT

In article <ftnPfAAWvmc4Ew4g@escore.demon.co.uk>,
aRJay  <roger@escore.demon.co.uk> wrote:
>Just to reveal my appalling ignorance, but what about using acetylene...

People have tried.  The problem is that pure liquid acetylene is a
powerful and extremely sensitive explosive.  (Commercial acetylene
cylinders store the stuff dissolved in acetone, which is reasonably safe
but unacceptably heavy for rocket applications.)

Quite a bit of work was done in the 1950s with various acetylene
derivatives.  Generally they are not very stable in storage, tend to
form impossibly sensitive peroxides on exposure to air, and often are
touchy explosives all by themselves.  Methylacetylene is one possible
exception.
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)

From: Bruce Dunn <bpdunn@home.com>
Newsgroups: sci.space.tech
Subject: Re: C7H8, RP-X2, Quadricyclene
Date: Thu, 27 Apr 2000 16:59:08 GMT

Henry Spencer wrote:

> The good news is that as a curtain coolant, it ought to lay down a lovely
> soot layer on the chamber wall, which will reduce heat transfer a great
> deal.  Soot deposition tends to scale quite strongly with the C:H ratio of
> the fuel.

Agreed.  Those who have used acetylene torches will no doubt remember
the horrible sooty flame of a torch running without enough oxygen.


> The bad news is that you don't want to do regenerative cooling with it;
> double bonds are bad enough for gunking up cooling passages, and I don't
> want to even think about triple bonds...


This may not be an intractable problem. The unsaturated molecules of
methylacetylene are small, and dimerization and trimerization leads to
products which are still relatively low molecular weight compounds
soluble in the bulk of the propellant.  Any polymerization products thus
formed will simply be carried along with the propellant and burned.
This is in contrast to the unsaturated compounds in kerosene which are
already a relatively high molecular weight and need little reaction to
form insoluble materials.

Industrially, to polymerize low molecular weight unsaturated
hydrocarbons into plastics, high temperatures, catalysts and substantial
time are needed. Rocket engine cooling passages lack the last two of
these elements.

In addition, it would appear quite feasible to add polymerization
inhibitors to the methylacetylene.  These are commercially available
products designed to block polymerization of highly reactive plastic
monomers during distillations and other processing.  The levels used in
these applications are typically on the order of 100 ppm, but higher
levels could be used in propellants with essentially no impact on their
suitability for use in a rocket engine.

Uniroyal Chemical for example markets a variety of polymerization
inhibitors under the trade name of Naugard:

http://www.uniroyalchemical.com/naugardi.htm

--------
Dr. Bruce Dunn
General Astronautics Canada, Vancouver B.C.
http://www.genastro.com/
Reliable, low-cost transportation to low Earth orbit and beyond