Methods and Uses for Intake-Valve and Direct-Injector Deposit Clean-Up

A method of improving the port fuel injection intake valve deposit clean-up performance or the direct injection fuel injector deposit clean-up performance of a fuel composition for use in a spark-ignition internal combustion engine which method comprises incorporating into the fuel composition in one or more steps:

• a. at least one hydrocarbyl-substituted aromatic compound, such as a Mannich Base detergent;
• and
• b. at least one polyalkylene amine, such as a polyisobutylene amine to produce a fuel composition which comprises said additives in combination and which on combustion in a spark-ignition engine produces greater port fuel injection intake valve or direct injection fuel injector deposit clean-up performance than the clean-up performance when combusting in said engine the fuel composition without said combination of additives.

A method of removing deposits from the intake valves in a port fuel injection spark-ignition internal combustion engine or the fuel injectors in a direct injection spark-ignition internal combustion engine which method comprises supplying to the engine through the port fuel injection intake valves or through the direct injection fuel injectors, a fuel composition which comprises a combination of:

• a. at least one hydrocarbyl-substituted aromatic compound, such as a Mannich Base detergent;
• and
• b. at least one polyalkylene amine, such as a polyisobutylene amine.