I've actually seen "perfume" for glow fuel... it's and additive to make your exhaust smell like grape, or other such goofy scent... can't imagine that it does much good for your engine, though! It was made/marketed for RC car engines, but probably could be used in planes as well... check them out...

http://www2.towerhobbies.com/cgi-bin...nt&FVPROFIL=++