Performance of a Catalyzed Diesel Particulate Filter System During Soot Accumulation and Regeneration

The trapping and regeneration behaviors of a diesel particulate filter (DPF), including particle size, are examined via engine dynamometer testing. The exhaust system consists of two active lean NO_x (ALN) catalysts in series followed by a catalyzed DPF. Forced regenerations are accomplished by injecting diesel fuel into the exhaust in front of the ALN catalysts to generate an exotherm sufficient to induce soot oxidation. Results are reported for two diesel fuels, one with 340 ppm sulfur, and the other with 4 ppm sulfur, and as a function of DPF regeneration temperature. The results show the DPF to be very effective at removing particulate matter, >99% efficiency. The <1% of particles that escape trapping exhibit a size distribution very similar to engine out soot. During regeneration, particle emissions remain well below engine out levels for the low sulfur fuel, but exhibit a temporary nucleation mode of about ten times the engine out level for the high sulfur fuel. The regeneration rate increases exponentially with temperature, and the fastest regenerations suffer the lowest fuel economy penalty.