The Effect of Combustion Chamber Deposits on Octane Requirement Increase in a Spark Ignition Engine

Intake valve deposits (IVD) and combustion chamber deposits (CCD) in spark-ignition engines greatly affect nitrogen oxides (NOx) emission and octane requirement increases (ORI) as they prevent the heat release from the combustion chamber and increase the compression ratio. Currently, fuel performance additives to control IVD and CCD have been attracted and evaluation method based on CCD weight and thickness has been widely used.

However, simple measurement of the CCD weight and thickness does not clearly reflect the CCD effect on the ORI, as the shape and location of the deposits are also crucial factors that must be considered along with the weight and thickness of the deposits.

In this paper, an ORI engine test procedure using a 4 cylinder 2.0 liter SOHC engine is introduced. Applying this test procedure, several combinations of fuels and additives are investigated in order to verify the CCD effect on the ORI, considering not only the weight and thickness of CCD but also their shape and location.