Effects of DPF Washcoat Variations on DPF Active Regeneration Characteristics

Three Cordierite diesel particulate filters (DPF) with variations in the washcoat^† (bare, washcoat-only, and catalyzed washcoat) were filled with equal amounts of PM (∼2 g/l) from a single steady-state engine operating condition (30% load, 1800 rpm). Two regeneration systems were used: an electrical furnace to extract the kinetic parameters by performing Temperature Programmed Oxidation (TPO) experiments and an inline burner to study how DPF washcoat variations affect active regeneration performance. Detailed emissions measurements were performed upstream and downstream of the DPF during the filtration and regeneration processes to quantify DPF filtration and regeneration performance. These measurements included gaseous emission, PM mass concentration, and particle size distribution.

Results from the furnace experiments showed that PM oxidation for a catalyzed washcoat DPF occurs in two distinct events, low temperature (LT) oxidation and high temperature (HT) oxidation, while PM oxidation in bare and washcoat DPFs only occurs in the HT event. Adding washcoat and catalyzed washcoat on the bare Cordierite substrate decreases the activation energy (E_A) during the HT event. It has been shown that with proper dilution conditions, increasing exhaust temperature by use of a burner has little effect on the PM mass and size distributions. Likewise, with appropriate dilution conditions, minimal secondary nucleation mode particles were detected during DPF regeneration. Though filtration performance of all examined filters was similar, their active regeneration behavior showed varied results in pressure drop and particle breakthrough. These differences are due to differences in their physical properties (porosity and mean pore diameter from the washcoat process) and chemical properties (E_A from the washcoat variations).