A Review of Engine Oil Oxidation Bench Tests and Their Application in the Screening of New Antioxidant Systems for Low Phosphorus Engine Oils

Abstract

A review of current oxidation and deposit bench tests used for the evaluation of engine oil performance will be presented. Some of the more meaningful tests will be utilized to evaluate a number of antioxidant systems for oxidation and deposit control capabilities in engine oils formulated with 470 ppm of ZDDP-derived phosphorus. The antioxidant components are selected from a series of commonly used and commercially available materials plus one new developmental component. These components include an organo-molybdenum compound (MoDTC), an alkylated diphenylamine (NDPA), a conventional hindered phenolic (HPE), a high performance hindered phenolic (MBDTBP), and a new multi-functional boronated MBDTBP. The performance of these fully formulated engine oils will be ranked in the selected bench tests in order to highlight the benefits of each antioxidant system under evaluation. The results point to significant benefits with the molybdenum- and boronated-systems, or mixed molybdenum-/boronated-systems, for oxidation control, while systems containing NDPA and MBDTBP are favored more for deposit control. Unique and superior performing antioxidant systems will be recommended for screening in fired engine and bench wear tests.

Elucidation of Low Molecular Weight Polymers in Vehicular Engine Deposits by Multidimensional Mass Spectrometry

“…This saturated hydrocarbon polymer is not detectable by MS techniques, unless it is derivatized with polar substituents. Such functionalization can, however, take place through thermal-oxidative degradation via radical intermediates in the vehicular engine , and/or the ASAP source . The PE oligomers detected are attributed to short, oxidized chains formed by such a process from PE leaked into the additives that ended up in the solid engine deposit analyzed.…”

“…Such PE chains can arise by oxidation of their CH 2 to CH­(OH) groups. ESI is a soft ionization method that generally does not alter analytes; hence, the oxidized PE species detected must have been formed in the vehicular engine, , from PE leaked into the additives (vide supra). It is noteworthy that the PE chains detected by ASAP-MS are more highly oxidized (cf.…”