NOVELTY - As a fuel additive or lubricant additive, a reaction product (P1) comprising a quaternized nitrogen compound, or its fraction which comprises a quaternized nitrogen compound and is obtained from the reaction product by purification, where the reaction product is obtainable by reacting a quaternizable alkylamine comprising at least one quaternizable tertiary amino group with a quaternizing agent which converts the tertiary amino group to a quaternary ammonium group, is used.    USE - As fuel additive, lubricant additive, gasoline fuel additive and diesel fuel additive, where the fuel is diesel fuels, biodiesel fuels, gasoline fuels, and alkanol-containing gasoline fuels (claimed).    ADVANTAGE - The fuel additive and lubricant additive reduces the fuel consumption of direct injection diesel engines, especially of diesel engines with common rail injection systems; minimizes power loss in direct injection diesel engines, especially in diesel engines with common rail injection systems; reduces the level of deposits in the intake system of a gasoline engine, such as especially Direct Injection Spark Ignition (DISI) and PFI (port fuel injector) engines; and reduces and/or prevents deposits in the injection systems, such as, more particularly, the internal diesel injector deposits (IDIDs), and/or valve sticking in direct injection diesel engines, especially in common rail injection systems.    DETAILED DESCRIPTION - As a fuel additive or lubricant additive, a reaction product (P1) comprising a quaternized nitrogen compound, or its fraction which comprises a quaternized nitrogen compound and is obtained from the reaction product by purification, where the reaction product is obtainable by reacting a quaternizable alkylamine comprising at least one quaternizable tertiary amino group with a quaternizing agent which converts the tertiary amino group to a quaternary ammonium group, where the quaternizing agent is the alkyl ester of a cycloaromatic or cycloaliphatic mono- or polycarboxylic acid, especially of a mono- or dicarboxylic acid, or of an aliphatic polycarboxylic acid, especially dicarboxylic acid, a hydrocarbyl/alkyl epoxide, optionally in combination with a free acid, or a dialkyl carbonate, is used. INDEPENDENT CLAIMS are included for the following:    (1) new quaternized nitrogen compound;    (2) a process of preparing a quaternized nitrogen compound involving: reaction of a quaternizable alkylamine comprising at least one quaternizable tertiary amino group with a quaternizing agent which converts the tertiary amino group to a quaternary ammonium group, where the quaternizing agent is the alkyl ester of a cycloaromatic or cycloaliphatic mono- or polycarboxylic acid, especially of a mono- or dicarboxylic acid, or of an aliphatic polycarboxylic acid, especially dicarboxylic acid, or a hydrocarbyl epoxide in combination with an acid;    (3) an additive concentrate comprising, in combination with further diesel fuel additives or gasoline fuel additives or lubricant additives, at least one of the quaternized nitrogen compound; and    (4) a fuel composition or lubricant composition comprising, in a majority of a customary fuel or lubricant, a proportion of at least one of the reaction product (P1).