Effect of metal‐free phosphorus anti‐wear compounds on passenger car emissions and fuel economy

There has been concern for many years that phosphorus (P) from engine oils is volatilised, passes through the combustion chamber and is deposited on the catalyst system in passenger cars, causing the emission control system to lose efficiency. Therefore, as new engine oil specifications have been introduced, there has been a trend to require a reduction in P in fresh engine oils. The primary P source in current engine oils is zinc dithiophosphate (ZDP), which acts as an anti‐wear agent and antioxidant. Therefore, a reduction in P in the oil could compromise the anti‐wear and antioxidant performance of engine oils. Another detrimental effect of ZDP is that it is known to increase friction in the mixed lubrication regime, which in turn would decrease the ability of engine oils to improve fuel economy. Metal‐free P‐containing anti‐wear additives (MFPAWs) have been used for many years in other automotive and industrial lubricants. We examined the effect of an MFPAW in catalyst efficiency and fuel economy engine tests. Catalyst protection and the fuel economy benefits of engine oils were improved when the MFPAW was used in place of ZDP. Therefore, the total P content of an engine oil does not need to be reduced if the proper anti‐wear additive is selected. Copyright © 2007 John Wiley & Sons, Ltd.