Detailed Diesel Exhaust Particulate Characterization and Real-Time DPF Filtration Efficiency Measurements During PM Filling Process 2007-01-0320

An experimental study was performed to investigate diesel particulate filter (DPF) performance during filtration with the use of real-time measurement equipment. Three operating conditions of a single-cylinder 2.3-liter D.I. heavy-duty diesel engine were selected to generate distinct types of diesel particulate matter (PM) in terms of chemical composition, concentration, and size distribution. Four substrates, with a range of geometric and physical parameters, were studied to observe the effect on filtration characteristics. Real-time filtration performance indicators such as pressure drop and filtration efficiency were investigated using real-time PM size distribution and a mass analyzer. Types of filtration efficiency included: mass-based, number-based, and fractional (based on particle diameter). In addition, time integrated measurements were taken with a Rupprecht & Patashnick Tapered Element Oscillating Microbalance (TEOM), Teflon and quartz filters.

Initial breakthrough phenomenon was observed for all clean DPFs. As the soot cake layer forms on top the substrate, the filtration efficiency is improved. In reality, the DPF substrate itself has poor filtration efficiency. It acts more as a facilitator to form a soot cake for the filtration of diesel particulates. A lower pressure drop filter (with approximately 70% larger filtration area than the others tested) showed considerably longer initial breakthrough. Results show different engine operating conditions resolve into distinct PM concentration, chemical composition, size distribution, and filtration velocity. Differences in the particulate composition and filtration characteristics appear to influence DPF pressure drop and filtration performance. Although the coating of the substrate contributes to higher pressure drop, it does not influence the onset of the different stages of filling. Comparing substrates with different geometrical and physical properties, a shift of the most penetrating particle range (Greenfield Gap) was observed.