The use of tetrahydrobenzoxazines I ##STR00001##
where R.sup.1 is a hydrocarbyl radical and R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently hydrogen atoms, hydroxyl groups or hydrocarbyl radicals, and where R.sup.2 to R.sup.5 may also form a second and a third tetrahydrooxazine ring, with the proviso that at least one of the substituents has from 4 to 3000 carbon atoms and the remaining substituents, when they are hydrocarbyl radicals, each have from 1 to 20 carbon atoms, as stabilizers for stabilizing inanimate organic material, especially turbine fuels, against the action of light, oxygen and heat.

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 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.

A method for reducing the propensity of a fuel to form an emulsion comprises combining 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 with the fuel. Thus, the additive may be used as a demulsifier in a fuel.

A method for reducing the propensity of a fuel to form an emulsion comprises combining 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 with the fuel. Thus, the additive may be used as a demulsifier in a 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 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.