Composition, method and use

A quaternary ammonium compound of formula (I) wherein X is a linking group; Y is O, NH or NR1 wherein R1 is H or optionally substituted hydrocarbyl group; Q+ is a moiety that includes a quaternary ammonium cation; A- is an anion; R2 is an optionally substituted alkylene group; R3 is hydrogen or optionally substituted hydrocarbyl group; and n is 0 or a positive integer, provided than n is not 0 when R3 is hydrogen. A composition comprising the quaternary ammonium compound of formula (I) is also claimed. The use of the quaternary ammonium compound of formula (I) as an additive in fuel, preferably gasoline, or in lubricating compositions; and a method of improving engine performance, comprising combusting a fuel composition comprising a quaternary ammonium compound of formula (I) are also disclosed. Preferably the quaternary ammonium salt is prepared by reacting a hydrocarbyl-substituted dicarboxylic acid or anhydride, most preferably succinic acid or anhydride, with an alcohol of formula R3(OR2)nOH; a reactive alcohol or amine including a tertiary amine, and a quaternising agent. Preferably, X is an optionally substituted alkylene group, most preferably ethylene. The compounds of the invention are useful in reducing and preventing build-up of injector deposits.