The ASTM Sequence VE test was developed to provide better discrimination than the ASTM Sequence V-D test when measuring the ability of oils to prevent sludge and varnish deposits and valve train wear. It is a key test in the definition of API SG oils. The formulation of API SG oils which provide superior performance as measured by the Sequence VE test depends largely on the type of dispersant which is used. By using statistical design methods in the synthesis of dispersants, the best dispersant can be defined in an efficient, cost-effective manner.
In order to develop a succinimide dispersant which could provide API SG performance, experimental design techniques were successfully used to optimize the experimental parameters. In the half replicate of a 23 or a Taguchi L4 design which was used, the three parameters selected were: two levels of dispersant molecular weight, two methods of derivatizing, and two types of amine. Statistical analyses of the Sequence VE data showed at the ninety percent or higher confidence level that the higher dispersant molecular weight improved sludge ratings, one of the derivatization methods improved average engine varnish ratings, and one of the amines improved average engine varnish ratings. Evaluation of the formulations in the single cylinder MWM-B diesel engine test confirmed that the diesel performance of the oil containing the optimized dispersant was not compromised.