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 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).