Understanding Soot Mediated Oil Thickening: Rotational Rheology Techniques to Determine Viscosity and Soot Structure in Peugeot XUD-11 BTE Drain Oils

The Association des Constructeurs Européen d'Automobiles (ACEA) light duty diesel engine specifications requires a kinematic viscosity measurement technique for Peugeot XUD-11 BTE drain oils. This viscosity measurement is used to define the medium temperature dispersivity of soot in the drain oil.(1)

This paper discusses the use of rotational rheology methods to measure the Newtonian character of XUD-11 drain oils. The calculation of the rate index using the Hershel Bulkley model indicates the level of non-Newtonian behavior of the drain oil and directly reflects the level of soot dispersion or agglomeration. This study shows that the more non-Newtonian the drain oil the greater the difference between kinematic and rotational viscosity measurements

Oscillation (dynamic) rheological techniques are used to characterize build up of soot structure. The storage modulus (G′) correlates with flow curve measurements for the ‘test pass’ drain oils and is inversely related to the rate index value. The more non-Newtonian the drain oil the higher the storage modulus and the lower the rate index. G′ is temperature dependent with structure build up occurring at 70-80°C for the more non-Newtonian drain oils. Increased soot level does not correlate to the levels of non-Newtonian behavior and soot structure build up. Structure build up is time dependent at temperatures where G′ is high and the drain is non-Newtonian.