Fuel management system for enhanced operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder. It is preferred that the direct injection occur after the inlet valve is closed. It is also preferred that stoichiometric operation with a three way catalyst be used to minimize emissions. In addition, it is also preferred that the anti-knock agents have a heat of vaporization per unit of combustion energy that is at least three times that of gasoline.

Fuel management system for enhanced operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder. It is preferred that the direct injection occur after the inlet valve is closed. It is also preferred that stoichiometric operation with a three way catalyst be used to minimize emissions. In addition, it is also preferred that the anti-knock agents have a heat of vaporization per unit of combustion energy that is at least three times that of gasoline.

Methods and systems are provided for accurately determining the composition of a knock control fluid using sensors already present in the engine system. An intake or an exhaust oxygen sensor is used to estimate the water and the alcohol content of a knock control fluid that is direct injected into an engine cylinder responsive to an indication of abnormal combustion. A change in the pumping current of the oxygen sensor due to the water content of the knock control fluid is distinguished from a change in the pumping current of the oxygen sensor due to the alcohol content of the knock control fluid.

Methods and systems are provided for accurately determining the composition of a knock control fluid using sensors already present in the engine system. An intake or an exhaust oxygen sensor is used to estimate the water and the alcohol content of a knock control fluid that is direct injected into an engine cylinder responsive to an indication of abnormal combustion. A change in the pumping current of the oxygen sensor due to the water content of the knock control fluid is distinguished from a change in the pumping current of the oxygen sensor due to the alcohol content of the knock control fluid.

The invention relates to the use of specific quaternised nitrogen compounds which are also subjected to specific transesterification or amidation, as a fuel and lubricant additive or kerosene additive, such as in particular as a detergent additive, for decreasing or preventing deposits in the injection systems of direct-injection diesel engines, in particular in common rail injection systems, for decreasing the fuel consumption of direct-injection diesel engines, in particular of diesel engines having common rail injection systems, and for minimizing the power loss in direct-injection diesel engines, in particular in diesel engines having common rail injection systems. The invention further relates to the use as an additive for petrol, in particular for operation of DISI engines.

The invention relates to the use of specific quaternised nitrogen compounds which are also subjected to specific transesterification or amidation, as a fuel and lubricant additive or kerosene additive, such as in particular as a detergent additive, for decreasing or preventing deposits in the injection systems of direct-injection diesel engines, in particular in common rail injection systems, for decreasing the fuel consumption of direct-injection diesel engines, in particular of diesel engines having common rail injection systems, and for minimizing the power loss in direct-injection diesel engines, in particular in diesel engines having common rail injection systems. The invention further relates to the use as an additive for petrol, in particular for operation of DISI engines.

A quaternary ammonium compound of formula (X):

##STR00001## wherein R.sup.0, R.sup.1, R.sup.2 and R.sup.3 is each individually an optionally substituted alkyl, alkenyl or aryl group and R includes an optionally substituted hydrocarbyl moiety having at least 5 carbon atoms.

A quaternary ammonium compound of formula (X):

##STR00001## wherein R.sup.0, R.sup.1, R.sup.2 and R.sup.3 is each individually an optionally substituted alkyl, alkenyl or aryl group and R includes an optionally substituted hydrocarbyl moiety having at least 5 carbon atoms.

Fuel management system for efficient operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder of the engine. A fuel management microprocessor system controls injection of the anti-knock agent so as to control knock and minimize that amount of the anti-knock agent that is used in a drive cycle. It is preferred that the anti-knock agent is ethanol. The use of ethanol can be further minimized by injection in a non-uniform manner within a cylinder. The ethanol injection suppresses knock so that higher compression ratio and/or engine downsizing from increased turbocharging or supercharging can be used to increase the efficiency or the engine.

Fuel management system for efficient operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder of the engine. A fuel management microprocessor system controls injection of the anti-knock agent so as to control knock and minimize that amount of the anti-knock agent that is used in a drive cycle. It is preferred that the anti-knock agent is ethanol. The use of ethanol can be further minimized by injection in a non-uniform manner within a cylinder. The ethanol injection suppresses knock so that higher compression ratio and/or engine downsizing from increased turbocharging or supercharging can be used to increase the efficiency or the engine.