Oxidation and Antiwear Retention Capability of Low-Phosphorus Engine oils

Abstract

Future vehicle emission regulations both in the US and Europe will require maintaining catalyst efficiency for longer mileage intervals. In order to achieve this requirement, chemical restrictions are being placed on elements in engine oil that can poison catalysts. Most of phosphorus and a significant amount of sulfur in current engine oils come from zinc dialkyldithiophosphates, ZDDPs, which are a class of cost-effective multifunctional additives providing wear, oxidation and corrosion protection. Reducing ZDDP concentrations raises oxidation and wear concerns. The overall purpose of this research is to look at the antioxidation and antiwear capability of low phosphorus engine oils containing 0.05 wt% phosphorus and the potential of engine oils formulated without phosphorus. In addition to fresh oils, used oils drained from fleet vehicles were also analyzed and evaluated. The results indicate that by appropriately selecting and balancing supplemental phosphorus-free antioxidation and antiwear additives the antioxidation capability can be improved for low phosphorus and even non-phosphorus oils, and the antiwear performance of low phosphorus oils could be maintained or even improved.