Fuel and Additive Effects on the Rates of Growth of Combustion Chamber Deposits in a Spark Ignition Engine

Combustion chamber deposits (CCD) increase more slowly with time and take longer to stabilise in a given engine test with a base fuel compared to the same base fuel with an additive package. In a short fixed-duration test the additive might appear to increase CCD levels significantly even though the stabilised CCD levels for the two fuels are not too different. When the same additive package is used in different base fuels, the fuels are ranked in the same order with or without the additive. However, the incremental increase in CCD because of the additive is more marked the cleaner the base fuel.