From:      skunk-works-digest-owner@mail.orst.edu
To:        skunk-works-digest@mail.orst.edu
Subject:   Skunk Works Digest V5 #350
Reply-To:  skunk-works-digest@mail.orst.edu
Errors-To: skunk-works-digest-owner@mail.orst.edu
Precedence: bulk

Skunk Works Digest        Wednesday, 12 July 1995      Volume 05 : Number 350

In this issue:

	Re: JP-7 fuel

See the end of the digest for information on subscribing to the skunk-works
or skunk-works-digest mailing lists and on how to retrieve back issues.

----------------------------------------------------------------------

From: Brad Hitch <hitch@hops.entertain.com>
Date: Wed, 12 Jul 1995 00:58:46 -0600 (MDT)
Subject: Re: JP-7 fuel

JP-7 was specially developed for the SR-71 to deal with the effect of 
high fuel temperatures.  Most jet fuels have components which react with 
the oxygen dissolved in them from the air when surface temperatures are 
above 325 degrees F or so.  The Jet Fuel Thermal Oxidation Test (JFTOT) 
is run to determine when fuel deposits form as a function of the 
temperature of a heated aluminum plate immersed in the fuel.  The test is 
graded on color.  The JFTOT breakpoint (where the fuel fails the test) is 
determined by running several tests at different temperatures.  JP-7 has 
a JFTOT breakpoint above 700 F.  This is a result of removing almost all 
non-saturated hydrocarbons by hydrotreating with hydrogen.  The military 
fuel specification forces this by specifying a very high heat of 
combustion, hydrogen to carbon ratio, and a very low aromatic content.  
The aromatic content is limited to minimize the radiation heat load on 
the combustor liner due to the sooting propensity of fuels containing 
six-membered carbon rings (such as benzene or napthalene).  Fuel 
producers tend to push the aromatics limit as much as possible since 
these components are expensive to remove and are fairly thermally stable.

The reason fuel thermal stability is a big issue is that gunk comes out 
of solution and fouls heat transfer surfaces, prevents the proper 
operation of fuel distribution valves, and distorts the fuel spray 
pattern and drop size distribution from the combustor fuel nozzles.  This 
can lead to a hot streak in the combustor exit gases which may impinge on 
a turbine nozzle, burning it up, or at least take some life out of 
turbine blades.

The JP-7 specification also requires a very low vapor pressure to reduce 
boil-off losses at high altitude and Mach numbers.  This is done by 
reducing the light end fractions, so no C4's, C5's, or C6's. The combination of 
requirements results in a fuel which is mostly C12-C14 parafins (branched 
and linear carbon chains saturated with hydrogen) and cyclo-parafins (circular 
parafins).  JP-7 is thus a very highly processed and $expensive$ fuel.

Just my $1.50 worth

Brad Hitch

------------------------------

End of Skunk Works Digest V5 #350
*********************************

To subscribe to skunk-works-digest, send the command:

    subscribe skunk-works-digest

in the body of a message to "majordomo@mail.orst.edu".  If you want
to subscribe something other than the account the mail is coming from,
such as a local redistribution list, then append that address to the
"subscribe" command; for example, to subscribe "local-skunk-works":

    subscribe skunk-works-digest local-skunk-works@your.domain.net

To unsubscribe, send mail to the same address, with the command:

	unsubscribe skunk-works-digest

in the body.

Administrative requests, problems, and other non-list mail can be sent
to either "skunk-works-digest-owner@mail.orst.edu" or, if you
don't like to type a lot, "prm@mail.orst.edu

A non-digest (direct mail) version of this list is also available; to
subscribe to that instead, replace all instances of "skunk-works-digest"
in the commands above with "skunk-works".

Back issues are available for anonymous FTP from mail.orst.edu, in
/pub/skunk-works/digest/vNN.nMMM (where "NN" is the volume number, and "MMM"
is the issue number).