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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.

Over the last decades, heavy duty diesel engines have experienced many changes in design and operation. More stringent emission legislation has been a driver for changes in the design of heavy duty diesel engines since the 1980s. Optimization of the combustion process and the introduction of exhaust gas recirculation allowed for significant reductions of exhaust emission levels over the years, but the thermal loading of the engine and its lubricant has increased. In the coming years, diesel engines will have to meet even more stringent requirements for particulate matter and nitrogen oxide emissions. These low emission diesel engines are expected to be equipped with exhaust gas after-treatment systems.

More stringent emission legislation has been a driver for changes in the design of Heavy Duty Diesel engines since the 1980s. Significant gains have been made over the years but, in 2007 and again in 2010, diesel engines in North America will have to meet even more stringent requirements for particulate matter and nitrogen oxide emissions. A reduction of the sulfur level in diesel fuel to a maximum of 15 mg/kg has been mandated as an enabler for new diesel engine exhaust gas after-treatment systems. Many studies have been published on the impact of the use of low sulfur diesel fuel. The focus of most of these studies has been on the possible impact on exhaust gas after-treatment system durability, but little has been documented on lubricant degradation and on the long term impact on engine durability. The objectives of the field test discussed in this paper were to evaluate the impact of low sulfur fuel and of a reduction in the TBN of the lubricant on lubricant degradation.

Two campaigns measuring on-road emissions of 23 VN-trucks on a randomly chosen driving cycle, consisting of 10 miles two-lane and 8 miles four-lane road were performed. The first, during October 2004, showed tailpipe NOx emissions on fleet average of 1.06 g/bhp-hr including the time the exhaust gas temperature was below 200°C. The second, during June 2005, showed tailpipe NOx emissions on fleet average of 1.13 g/bhp-hr including the time the exhaust gas temperature was below 200°C. Complementary measurements in a SET-cycle (13 point OICA-cycle) on a chassis dynamometer showed a tailpipe emission of 0.008 g PM per bhp-hr. Moreover, cost analysis show that the diesel fuel consumption remains unchanged whether the truck running on ULSD is equipped with a Combined Exhaust gas AfterTreatment System (CEATS) installed or not.