Abstract: The soot sonication dispersion method for CJ-4 engine oil was established by simulation to relate the results of Mack T-11 engine test. The influence of different dosage ashless dispersants on the dispersion ability and shear stability was investigated. The results show that the ashless dispersants with different molecular structure have different dispersion abilities for soot dispersion. Good dispersion ability and shear stability can be observed at suitable dosage of the ashless dispersants and less influence on the oil shear ability is found. The CJ-4 diesel engine oil with the optimum amount of dispersant passes the Mack T-11 engine test.

Key words: engine test, simulation test, soot, ashless dispersant, shear stability