Synergistic effects of lubricant additive chemistry on ash properties impacting diesel particulate filter flow resistance and catalyst performance

Abstract

Diesel particulate filters (DPF) have seen widespread use in recent years in both on- and offroad applications as an effective means for meeting the increasingly stringent particulate emission regulations. Overtime, engine-out particulate matter composed of soot and incombustible ash accumulate within the DPF. Although soot can be removed by oxidation, ash remains within the filter and substantially accumulates over time leading to increased flow restriction thus a pressure drop across the filter. An increased pressure drop negatively affects the engine performance & fuel economy leading to the need for filter removal and cleaning. The adverse effects of ash accumulation on DPF performance have been extensively studied in the past and are well know yet the underlying mechanisms for their presence are still not well understood. The ash which accumulates within a DPF is a product of a number of factors including engine wear and corrosion as well as trace metals in diesel fuel, but the majority of the engine out ash is derived from specific metallic additives placed within the diesel lubricant. This work examines the properties of ash derived from specific single lubricant additives, as well as simple combinations, and their adverse effect on DPF performance. Specific ash properties are examined such as porosity, permeability, deposit thicknesses and packing densities along the filter channel walls as a cake layer as well as the resultant end plugs in the rear of the filter channels. Through a combined approach of experiments and theoretical models, the link between the material properties and characteristics of ash derived from single additives as well as combinations can be made to their respective impact on DPF performance. The results of this research are among a few of its kind and aim to help optimize the design of advanced diesel aftertreatment systems as well as lubricant formulations to satisfy the additive requirements for engine protection while mitigating the negative effects on DPF performance.