From: utzoo!decvax!ucbvax!CAD:tektronix!zehntel!zinfandel!berry Newsgroups: net.cycle Title: Re: Re: leaded vs unleaded gasoline - (nf) Article-I.D.: zehntel.751 Posted: Mon Feb 14 13:18:03 1983 Received: Mon Feb 21 06:42:59 1983 #R:tekmdp:-176800:zinfandel:4600002:000:1102 zinfandel!berry Feb 14 09:38:00 1983 True, octane is a saturated 8-carbon hydrocarbon, but the 'octane rating' determines whether a given blenfd of gasoline is 'premium' or not. The 'octane rating' is NOT the ratio of octane to heptane or any perversion of this number. The 'octane rating' displayed on gas pumps is the average of the 'Research method octane number' and the 'motor method octane number'. In the research method chemical wizards perform arcane rites of analysis on a sample of the gas and come up with a magic number indexed to 'iso-octane's' magic number (usually 100). (iso-octane is the isomer of octane with all 8 carbon atoms in a (more or less) straght line). The motor method consists of running the gasoline sample into an ANSI standard 1-cylinder Otto-cycle engine (Really!) and fiddling with the operating parameters (compression, spark, mixture etc.) until it starts knocking. An 'octane number' is derived from these parameters. Research numbers tend to be several points lower than motor numbers, hence the average. Berry Kercheval Zehntel Inc. (decvax!sytek!zehntel!zinfandel!berry) (415)932-6900