A fuel composition for a spark-ignition internal combustion engine comprises a non-metallic octane-boosting additive. The non-metallic octane-boosting additive is an additive which, when used at a treat rate of 0.67 % by weight, increases the research octane number of a fuel by at least 1.8 whilst maintaining the T.sub.90 and/or the vapour pressure.

A fuel composition for a spark-ignition internal combustion engine comprises a non-metallic octane-boosting additive. The non-metallic octane-boosting additive is an additive which, when used at a treat rate of 0.67 % by weight, increases the research octane number of a fuel by at least 1.8 whilst maintaining the T.sub.90 and/or the vapour pressure.

An additive composition for use in a fuel for a spark-ignition internal combustion engine comprises an octane-boosting additive and one or more further fuel additives. The octane-boosting additive has a chemical structure comprising a 6-membered aromatic ring sharing two adjacent aromatic carbon atoms with a 6- or 7-membered saturated heterocyclic ring, the 6- or 7-membered saturated heterocyclic ring comprising a nitrogen atom directly bonded to one of the shared carbon atoms to form a secondary amine and an atom selected from oxygen or nitrogen directly bonded to the other shared carbon atom, the remaining atoms in the 6- or 7-membered heterocyclic ring being carbon. The additive composition increases the octane number of the fuel, thereby proving the auto-ignition characteristics of a fuel.

An additive composition for use in a fuel for a spark-ignition internal combustion engine comprises an octane-boosting additive and one or more further fuel additives. The octane-boosting additive has a chemical structure comprising a 6-membered aromatic ring sharing two adjacent aromatic carbon atoms with a 6- or 7-membered saturated heterocyclic ring, the 6- or 7-membered saturated heterocyclic ring comprising a nitrogen atom directly bonded to one of the shared carbon atoms to form a secondary amine and an atom selected from oxygen or nitrogen directly bonded to the other shared carbon atom, the remaining atoms in the 6- or 7-membered heterocyclic ring being carbon. The additive composition increases the octane number of the fuel, thereby proving the auto-ignition characteristics of a fuel.

A method for preparing a fuel composition which comprises a base fuel, an oxygenate and an octane-boosting additive comprises: blending an additised oxygenate with a base fuel, wherein the additised oxygenate comprises an oxygenate and an octane-boosting additive. The method enables suitable amounts of octane-boosting additives to be incorporated into a fuel composition, whilst enabling fuels having a range of properties to be prepared.

A method for preparing a fuel composition which comprises a base fuel, an oxygenate and an octane-boosting additive comprises: blending an additised oxygenate with a base fuel, wherein the additised oxygenate comprises an oxygenate and an octane-boosting additive. The method enables suitable amounts of octane-boosting additives to be incorporated into a fuel composition, whilst enabling fuels having a range of properties to be prepared.

A fuel composition for a spark-ignition internal combustion engine comprises an additive having a chemical structure comprising a 6-membered aromatic ring sharing two adjacent aromatic carbon atoms with a 6- or 7-membered saturated heterocyclic ring, the 6- or 7-membered saturated heterocyclic ring comprising a nitrogen atom directly bonded to one of the shared carbon atoms to form a secondary amine and an atom selected from oxygen or nitrogen directly bonded to the other shared carbon atom, the remaining atoms in the 6- or 7-membered heterocyclic ring being carbon. The additive increases the octane number of the fuel, thereby improving the auto-ignition characteristics of the fuel.

A fuel composition for a spark-ignition internal combustion engine comprises an additive having a chemical structure comprising a 6-membered aromatic ring sharing two adjacent aromatic carbon atoms with a 6- or 7-membered saturated heterocyclic ring, the 6- or 7-membered saturated heterocyclic ring comprising a nitrogen atom directly bonded to one of the shared carbon atoms to form a secondary amine and an atom selected from oxygen or nitrogen directly bonded to the other shared carbon atom, the remaining atoms in the 6- or 7-membered heterocyclic ring being carbon. The additive increases the octane number of the fuel, thereby improving the auto-ignition characteristics of the fuel.

Use of a hydrocarbyl-substituted dicarboxylic acid for improving or boosting the separation of water from fuel oils and gasoline fuels which comprise additives with detergent action. A Fuel additive concentrate comprising the said hydrocarbyl-substituted dicarboxylic acid, certain additives with detergent action and optionally other customary additives and solvents or diluents.

A method is provided for preparing a fuel additive having the formula: (1) The method comprises carrying out the following reactions: (i) addition of an alkylating agent b to starting material a: (a) to form an intermediate c; and (ii) ring closing intermediate c to form fuel additive e.

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