Development of Low Phosphorous Engine Oils

ZDDP is the industry standard anti wear additive used by oil formulators for the past 50 years to provide the antiwear and load bearing capacity of engine oil. The breakdown of ZDDP results in the formation of sulfides and phosphates which provide anti-wear protection. In addition to its role as an anti-wear additive ZDDP also performs the role of an antioxidant. The performance of ZDDP is reduced by other parts of the additive package which include dispersants, pH stabilizers, and detergents. These constituents stabilize ZDDP and reduce its activity. The breakdown of ZDDP also creates S and P that can poison catalytic converters resulting in higher hydrocarbon and NOx emissions. GF-4 oils have lower ZDDP content to meet federal emission standards. In addition, to meet CAFE´ fuel economy standards, the industry is moving towards lower weight 5W-20 oil. The lower weight base oil coupled with lower ZDDP content have put additional constraints in developing high performance GF-4 oil. An additive package developed by Platinum Research Organization and the Tribology Group at University of Texas at Arlington is evaluated. This additive package enhances the activity of ZDDP and increases its anti-wear performance. This paper presents results from bench top tribology tests that were conducted to evaluate the performance of GF-4 oils with different amounts of ZDDP, additive package and an Fe based active ingredient. Results are discussed with respect to the extent of wear for a fixed number of wear cycles in a ball on cylinder test conducted under boundary conditions. In the presence of FeF3 active ingredient fully formulated oils with as little as 0.01% P exhibits antiwear performance comparable to oils with as much as 0.05% P and oils with 0.05%P are comparable to oils with 0.1%P. Differential scanning calorimetry indicates that the decomposition temperature of ZDDP is reduced by as much as 20°C in the presence of FeF3. This reduced decomposition temperature results in the efficient formation of anti-wear films even with lower ZDDP amounts.