Effects of Aftertreatment on Semi-Volatile Particulate Matter Emissions from Low Temperature Combustion in a Light-Duty Diesel Engine

Diesel low temperature combustion (LTC) is an operational strategy that effectively limits soot and oxides of nitrogen (NOx) emissions in-cylinder. Unfortunately, LTC results in increased hydrocarbon emissions as compared to conventional diesel combustion (CDC). Previous work has shown that exhaust conditions resulting from LTC inhibit oxidation of HC within a diesel oxidation catalyst (DOC). Further, these elevated HC emissions result in engine-out particulate matter (PM) that primarily consists of semi-volatile organic material. The current work shows that a DOC incompletely oxidizes this PM forming material. These results investigated the effectiveness of both a DOC and a diesel particulate filter (DPF) in reducing particle emissions for LTC. In this work, engine-out, DOC-out, and DPF-out exhaust were sampled using a micro-dilution system. Particle distributions were determined with a scanning mobility particle sizer (SMPS) and engine exhaust particle sizer (EEPS). A catalytic stripper (CS) was used to differentiate volatile and solid material in the PM. A Fourier Transform Infrared (FTIR) analyzer was used for light HC speciation. Soot concentrations were determined using a photo-acoustic sensor (Microsoot). The study revealed that a DOC is only partially effective at eliminating PM from LTC exhaust, with a DPF reducing LTC particle emissions further, despite the particle volatility. However, the results show that as aftertreatment HC loading increases, the storage ability is compromised, and its PM removal efficiency is lessened. This suggests that a DOC-DPF aftertreatment system can effectively remove PM from LTC exhaust as long as DPF regeneration occurs during the operating cycle.