1997-05-01

Understanding Soot Mediated Oil Thickening Through Designed Experimentation Part 3: An Improved Approach to Drain Oil Viscosity Measurements - Rotational Rheology 971692

Lubricating oil viscosity is commonly measured by the kinematic method as outlined in ASTM 0445. This method is also used to measure drain oil viscosity as an indicator of soot induced thickening. Drain oils can contain solid particles and exhibit non-Newtonian flow behavior.
This paper discusses the use of rotational rheometers to measure the rheology of drain oils. These instruments have been used for many years in other industries (food, paints and coatings) to measure particle filled, non- Newtonian fluids. The rotational method yields the general flow curve of viscosity versus shear rate as compared to the single point, low shear kinematic viscosity measurement. The rotational method includes the kinematic viscosity single point but also yields significantly more information on shear behavior. Both pumpability (low shear) and flowability(higher shear) can be ascertained from the rotational method.
Various geometry used in rotational methods will be discussed along with controlled stress versus controlled rate rheometers. The specific requirements of a procedure are outlined along with considerations for preshear conditioning, equilibration, temperature and time effects. Data analysis of the curves and simplification with an empirical model are also presented.
Results include data from a number of different engine drain oils. This will include Newtonian oils with high and low soot levels and non-Newtonian oils with high and low soot levels. The above mentioned methods and procedures will be used to analyze these systems and demonstrate the procedure and analysis.

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