Evaluation of Dispersant Viscosity Modifiers for the Application of Controlling Soot-related Viscosity Increase in EGR-Enabled Diesel Engines

This paper describes the effectiveness of an array of dispersant viscosity modifiers (DVMs) in controlling soot-related viscosity increase. Using a controlled stress rheometer in conjunction with rotational and oscillatory rheological methods the DVM chemistries were assessed. A Cummins M11 engine fitted with EGR was used to generate a DVM-free, heavily sooted oil. Evaluation was achieved by subsequent addition of DVM to this drain oil. A yield stress test was employed to evaluate the flow curve of each, with good dispersant viscosity modifiers displaying improved rotational viscosity at the yield point. An oscillation technique was employed to evaluate the elastic modulus (G′) and the viscous modulus (G″) which together contribute to the overall fluid behavior. Clear differentiation was achieved for the range of DVMs tested with regards to their ability to disperse soot, with DVMs 1 and 3 performing the best when equivalent active polymer concentration were compared. DVM 6 performed equally well but required a greater active polymer concentration. DVM 4 performed the worst, having a deleterious effect on viscosity.