The nature of lubricant-derived ash-related emissions and their impact on diesel aftertreatment system performance

Abstract

Diesel particulate filters (DPF) have seen widespread use in on- and off-road applications as an effective means for meeting increasingly stringent particle emissions regulations. Over time, incombustible material or ash, primarily derived from metallic additives in the engine lubricant, accumulates in the DPF. Ash accumulation leads to increased flow restriction and an associated increase in pressure drop across the particulate filter, negatively impacting engine performance and fuel economy, and eventually requiring filter removal for ash cleaning. While the adverse effects of ash accumulation on DPF performance are well known, the fundamental underlying mechanisms controlling these effects are not. This work explores the parameters influencing key ash properties such as porosity and permeability, and factors controlling the soot deposition - ash formation/accumulation process, which ultimately determines the magnitude of the ash effect on DPF pressure drop. In addition to the ash properties, the location of ash deposit accumulation inside the DPF channels, whether in a cake layer along the filter walls or packed in a plug at the rear of the channels, also plays a major role in influencing DPF pressure drop. Through a combined approach employing targeted experiments and theoretical models, explanations for the key factors and processes controlling ash properties and their effects on DPF pressure drop were developed.

(cont.) These results, among few fundamental data of this kind, correlate changes in diesel particulate filter performance with lubricant chemistry, exhaust conditions, and ash morphological characteristics. Results are useful in optimizing the design of the combined engine-aftertreatment-lubricant system for future diesel engines, balancing the requirements of additives for adequate engine protection with the requirements for robust aftertreatment systems.