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Thermal barrier coated diesel engines, also known as low heat rejection (LHR) engines, have offered the promise of reducing heat rejection to the engine coolant and thereby increasing overall thermal efficiency. However, the larger market potential for thermal barrier coated engines may be in retrofitting in-service diesel engines to reduce particulate emissions. Prior work by the authors has demonstrated a significant decrease in particulate emissions from a thermal barrier coated, single-cylinder, indirect injection (IDI) diesel engine, primarily through reduction of the volatile (VOF) and soluble (SOF) fraction of the particulate. This prior work relied on conventional, commercially available, petroleum-based lubricants. The present study concerns the additional benefits for particulate reduction provided by vegetable oil lubricants. These lubricants are derived from renewable resource materials and can provide a reduction in lubricant generated particulate matter.

Current specifications for automatic-transmission fluids and gear oils have viscosity limits which are determined by ASTM D 2983. However, that test is plagued by poor precision. This paper describes the development of a method using the Mini-Rotary Viscometer to make the determination of apparent viscosity at the same nominal shear stress as ASTM D 2983. In this test procedure, samples are cooled in a manner similar to that described in ASTM D 2983. Experimental data were obtained on a mixture of 17 automatic-transmission and gear-oil fluids that included a number of different formulation strategies and commercial products. The results of this method yield a nearly one to one correlation with the results determined by ASTM D 2983.