McGeehan, J., Van Dam, W., Narasaki, K., Boffa, A. et al., "Extending the Boundaries of Diesel Particulate Filter Maintenance With Ultra-Low Ash - Zero-Phosphorus Oil," SAE Int. J. Fuels Lubr. 5(3):1240-1263, 2012, doi:10.4271/2012-01-1709.
By 2014, all new on- and off-highway diesel engines in North America, Europe and Japan will employ diesel particulate filters (DPF) in the exhaust in order to meet particulate emission standards. If the pressure across the DPF increases due to incombustibles remaining after filter regeneration, the exhaust backpressure will increase, and this in turn reduces fuel economy and engine power, and increases emissions.Due to engine oil consumption, over 90% of the incombustibles in the DPF are derived from inorganic lubricant additives. These components are derived from calcium and magnesium detergents, zinc dithiophosphates (ZnDTP) and metal-containing oxidation inhibitors. They do not regenerate as they are non-volatile metals and salts. Consequently, the DPF has to be removed from the vehicle for cleaning.Ashless oil could eliminate the need for cleaning. This study initially focused on development of an ashless oil, but eventually concluded that this oil could not meet the valve-train wear requirements of the API CJ-4, SN/ACEA E9 oil categories. However, a zero-phosphorus oil with no ZnDTP and an extremely low sulfated ash of 0.4% demonstrated that it could meet critical engine tests in API CJ-4/ACEA/SN. Passing results for piston deposit and oil consumption were also achieved in the Daimler 501LA and VW TDi engine tests, which are part of several ACEA oil categories.The above oil, which has been optimized at 0.3% sulfated ash, has proven field performance in Cummins ISX engines and should extend the cleaning interval of the DPFs. The engine wear and viscosity control at oil drains of 97,000 km (60,000 miles) equals that of API CI-4 PLUS/ACEA E7 at 1.4% sulfated ash oil. This study demonstrated that the oil's total base number (TBN) is not a critical factor in controlling wear with engines using Ultra-Low Sulfur Diesel (ULSD) fuel.