Patent ID: 7901470

Claim:
A method of operating a direct injection spark ignition engine with reduced fouling of injector nozzles, which comprises running the engine on an unleaded gasoline composition comprising a major proportion of a gasoline suitable for use in a spark ignition engine, 10 to 1000 ppmw based on the gasoline composition of a hydrocarbyl primary monoamine having a number average molecular weight in the range 155 to 270, and 50 to 2000 ppmw based on the gasoline composition of a high molecular weight nitrogen-containing detergent containing a hydrocarbyl group having a number average molecular weight in the range 750 to 6000, wherein the hydrocarbyl primary monoamine comprises at least one linear alkylamine of formula CH 3 (CH 2 ) n NH 2 (I) wherein n is 9 to 17.