Development of zero‐phosphorus engine oils

Abstract

Poisoning by phosphorus in engine oil limits the useful life of automotive catalysts. The amount of phosphorus in engine oil has been decreasing for over a decade, and currently is limited to 0.08 wt% maximum. The source of phosphorus in engine oil is zinc dialkyldithiophosphate, which is a very effective antioxidant and anti‐wear compound. Therefore, elimination of phosphorus in engine oil requires replacement of both anti‐wear and antioxidation functions with novel additive compounds. This research describes the current state of developing zero‐phosphorus engine oils while maintaining GF‐4 performance attributes. A systematic approach was taken for this development beginning with the base oil and viscosity modifier system selection, followed by antioxidant compounds selection, and then anti‐wear compound selection. The effectiveness of antioxidant and anti‐wear compounds was evaluated using a laboratory oxidation test, and friction and wear tests when the oil was both fresh and aged. The oil showing the most promising result was evaluated in industry accepted TEOST MHT 4 for oxidation, and ASTM Sequence IIIG test for high temperature wear and piston deposits. Results to date show excellent oxidation characteristics, but wear control requires further work. Analysis of surface films showed the presence of carbonate and iron oxide when the oil was fresh, but only iron oxide when tested with 40 and 100 h aged oil samples from the Sequence IIIG test. Copyright © 2007 John Wiley & Sons, Ltd.

Soot–additive interactions in engine oils

“…[14][15][16][17] We have found that using a combination of different tools gives a more complete chemical and morphological picture of the surface fi lm than using a single individual technique.…”

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“…Zinc dialkyldithiophosphate (ZDDP) has been an effective and versatile AW/EP agent with antioxidation and anticorrosion-enhancing capabilities, 85,86 but is gradually losing attraction because of its environmental disadvantages (high sulphated ash, phosphorus and sulphur content), and potentials of forming electrolytic corrosive salts, when subjected to tribological loadings. 19,85,[87][88][89] ZDDP (secondary/aryl), noted to be hydrolytically unstable, 35,86 may aggravate the hydrolytic weakness of VOs, and the zinc being a reactive metal 90 can be an oxidation stimulator. Sulfur, one of the ingredients of ZDDP, has been suspected to cause corrosion wear in rapeseed oil.…”

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“…Moreover, the International Lubricant Standardization and Approval Committee (ILSAC) provided the GF-5 performance standards that place limits of 0.08% max. on phosphorus in the finished engine oils, so as to improve fuel economy, environmental protection, and emissions system compatibility [11][12][13]. So, it is desirable to partially or totally replace ZDDP with other lubricant additives without reducing the performances of formulated engine oils.…”