Phosphorus is known to reduce the effectiveness of the three-way catalysts commonly used by automobile manufacturers by deactivating the catalyst. This process occurs as zinc dialkyldithiophosphate (ZDP) decomposes in the engine oil, creating many phosphorus species, which provide excellent wear protection of the engine but can also interact with the active sites of the three-way catalyst. This reactivity has led to API specifications for engine oils with lower concentrations of phosphorus. In order to further minimize catalyst deactivation without compromising wear protection, a novel ZDP technology was designed for engine oil applications. This novel ZDP was designed to minimize the amount of phosphorus produced via volatilization during engine operation while maintaining engine wear protection.
In order to prove the efficiency of this novel technology, a field trial was conducted in New York City taxi cabs to compare API SM quality oils formulated with conventional ZDP and this novel ZDP. At test completion, the vehicles' engines all had very little wear, which indicated that wear protection was maintained when changing ZDP. The used oil analyses clearly indicated higher %P retention in the oils formulated with the novel ZDP, hence less phosphorus was lost due to volatility when using these oils. Emissions data collected after the trial showed the catalysts in the vehicles run on the oil containing the novel ZDP were more efficient than those run on oil containing conventional ZDP.
New emissions legislation is now causing marine engine manufacturers to consider utilizing three-way catalysts on four-stroke engines. Engine manufacturers made a request at the February 2008 National Marine Manufacturers Association Oil Certification Committee meeting that the organization considers developing a performance category to define catalyst-friendly FC-W oils. In order to meet this emerging need, the novel ZDP technology was used to develop several potential catalyst-friendly FC-W (Four Cycle Water-cooled) oils for boating applications. These oils were evaluated in a field trial using Yamaha 115HP engines. The key finding from this study was that as the %P was lowered, wear protection was maintained. In addition, analysis of the used oil clearly indicated higher %P retention in the oils formulated with the novel ZDP technology.
It has been demonstrated that catalyst-friendly engine oils can be developed. As marine manufacturers consider utilizing three-way catalysts, they should carefully consider the quality of oil specified for those engines in order to maximize the efficiency and the life of those catalysts without compromising engine durability.