Polymers as additives for fuels

A method, comprising:

• injecting a diesel fuel into a direct injection diesel engine through a fuel system in fluid communication with the direct injection diesel engine, wherein the fuel system comprises an injection system having injection nozzles and a common rail, and
• combusting the diesel fuel in the direct injection diesel engine;
• wherein the diesel fuel comprises at least one copolymer in an amount effective for reducing the formation of internal ionic and/or polymeric deposits in the injection nozzles of the injection system in comparison to a method of injecting and combusting the same amount of a comparative fuel that is the same as the diesel fuel but does not contain the copolymer;
• wherein the copolymer comprises, in a copolymerized form:
• (A) maleic anhydride,
• (B) an α-olefin having from 12 to 30 carbon atoms,
• (C) optionally an additional aliphatic or cycloaliphatic olefin which has at least 4 carbon atoms and is different from monomer (B) and
• (D) optionally an additional copolymerizable monomers other than monomers (A), (B) and (C), selected from the group consisting of
• (Da) a vinyl ester,
• (Db) a vinyl ether,
• (Dc) a (meth)acrylic ester of an alcohol having at least 5 carbon atoms,
• (Dd) an allyl alcohol or an ester thereof,
• (De) a N-vinyl compound selected from the group consisting of a vinyl compound of a heterocycle containing at least one nitrogen atom, a N-vinylamide and a N-vinyllactam,
• (Df) an ethylenically unsaturated aromatic,
• (Dg) an α,β-ethylenically unsaturated nitrile,
• (Dh) a (meth)acrylamide, and
• (Di) an allylamine,
• wherein the copolymer has one or more anhydride functionalities reacted with the compound (E) comprising an alcohol group and/or an amino group, and at least a portion of the anhydride functionalities are hydrolyzed.