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From: Bruce Dunn <>
Subject: Re: C7H8, RP-X2, Quadricyclene
Date: Thu, 20 Apr 2000 16:46:37 GMT

While MAPP gas is available commercially, it is also possible to
purchase methylacetylene/propadiene as a specialty chemical, without the
propane and propylene in it (methylacetylene and propadiene are both
C3H4, and commercial methylacetylene will always contain some propadiene
in it due to isomerization).  Methylacetylene is  CH3-C-(triple
bond)-CH, while propadiene is  CH2=C=CH2

The vapor pressure of methylacetylene is lower than that of MAPP gas,
and the density is higher due to the elimination of the propane (C3H8)
and propylene (C3H6).  At 20 C, the vapor pressure is 0.492 MPa, and the
density about 610 kg/m^3.  It should be possible to take commercial MAPP
gas, and with a sealed distallation setup with a reasonably efficient
fractionation column remove most of the propane and propylene (which
have vapor pressures of 0.83 and 1.01 MPa at the same temperature,

It is probably simplest to use methylacetylene at its normal boiling
point 250 K, where its density is about 670 kg/m^3.  A vented tank will
stay at this temperature during pre-launch activities, cooled by the
evaporation of the hydrocarbon.  This isn't even remotely cryogenic -
the cooling coils of a domestic freezer get colder than this.

Burned with liquid oxygen, the theoretical exhaust velocity of
methylacetylene (C3H4) is about 3.5 % higher than that of kerosene, but
the bulk density including both the fuel and oxidizer is about 10%
lower.  This is favorable compared with methane (CH4), which has an
exhaust velocity of about 3.8% higher than kerosene, but a bulk density
of 22% lower (both hydrocarbons assumed to be at their normal boiling
point at atmospheric presure).

Dr. Bruce Dunn
General Astronautics Canada, Vancouver B.C.
Reliable, low-cost transportation to low Earth orbit and beyond

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