The Role of Lubricant Additives in Controlling Abnormal Combustion (ORI)

This paper reviews the effects of several lubricant related variables on abnormal combustion. The effects of basestocks, sulfated ash level, metal detergent type, and viscosity improver are discussed. The data indicate that improved customer satisfaction can be achieved by design of lubricant type and additive components. Ashless or low sulfated ash oils, and those formulated with hydrocarbon viscosity improvers are shown to contribute less toward ORI and other types of abnormal combustion. In addition, the choice of metal detergent is found to be important. The range of improvement can be as much as 4 octane units. An attempt is made to relate viscosity improver structure to stability and combustion chamber deposit forming tendency. Laboratory, engine, and field test data are presented.