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From: Doug Jones <>
Subject: Re: Propane/LOX
Date: Mon, 17 Jan 2000 17:55:28 -0800

Robert Lynn wrote:
} "Paul F. Dietz" wrote:
} > The advantage I've heard of propane over kerosene is not
} > its performance, but rather for cleaning reusable engines.
} > Propane is easily cleaned from the system after use --
} > just let it boil off.  Residual kerosene is harder to remove.
} > And you don't want any of that residual kerosene getting
} > into the oxidizer plumbing.
} Kerosene suitable for rockets, RP-1 or its Russian equivalent, has to be
} refined to remove various species that could harm the engine through
} coking in the coolant channels.  This makes it more expensive and very
} uncommon.  I think that Propane is far less susceptible to coking in the
} coolant channels than kerosene.  IIRC that is the reason Gary Hudson et
} al they wanted to use use LOX cooling for the Roton RocketJet engine,
} because ordinary kerosene was not suitable for cooling.

LOX cooling did work quite well, even when the combustion chamber had a
significant crack which allowed cold oxygen to leak into the chamber
through the wall.  LOX can't coke even when abused :)  (For the RocketJet
engine, LOX cooling was required due to the LOX having the greater pressure
budget available for cooling, as well as having more enthalpy available to
cool the combustors.)

On the other hand, the only processing needed to make propane low-fouling
is to subcool it once to around 95 K- the higher hydrocarbons and sulfur
compounds freeze out; the sulfur is the real problem and low sulfur
kerosene doesn't foul badly either, so probably the best solution is to pay
the refinery extra to clean it up.  Environmental protection laws are
driving toward low-sulfur diesel and jet fuels, so the desulfurization
equipment will be amortized over a much larger user base.  This may end up
being the simplest solution.

On the gripping hand, the most annoying thing about kerosene for reusable
engines is the cleanup- soot, sludge, and oil get onto and into
*everything* and getting it our of the oxygen system ain't easy.  This I
know from personal experience, and volatile zero-residue fuels in general
are attractive because of it.

Doug Jones
Rocket Plumber, XCOR Aerospace

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