High octane unleaded aviation gasoline

Abstract

An unleaded aviation fuel blend. The fuel blend is provided by blending an unleaded aviation gasoline base fuel which may include iso-octane and iso-pentane, and an effective amount of a selected alkyl benzene to improve the functional engine performance to avoid harmful detonation sufficient to meet or exceed selected standards for detonation performance requirements in full scale aircraft piston spark ignition engines designed for use with Grade 100LL avgas. Advantageous alkylated benzenes include those having a meta-ring position between alkyl groups. Alkyl groups may be provided at least in part by methyl groups. In an embodiment, the alkyl benzene may include 1,3-dimethylbenzene. In an embodiment, two or more alkylated benzenes may be provided. In an embodiment, 1,3,5-trimethylbenzene may be provided. Suitable alkylated benzenes may include a mixture of xylene isomers. Selected aromatic amines, such as m-toluidine, may also be added to increase motor octane number.

I claim: 
     
         1 . In an existing aircraft engine mechanically designed for use by combustion of a leaded aviation gasoline fuel having 99.6 motor octane number (MON) or better leaded aviation gasoline, said engine utilizing a spark ignition system with pistons in cylinders, a process comprising
 substitution of said leaded aviation gasoline fuel with an unleaded aviation fuel blend, said unleaded aviation fuel blend comprising an (a) aviation gasoline base fuel, and (b) a selected alkyl benzene, said selected alkyl benzene comprising methyl groups in a meta-ring position, (c) up to about twenty percent (20%) by weight of C 4  to C 5  paraffins, and (d) butane.