An Experimental and Computational Study of the Pressure Drop and Regeneration Characteristics of a Diesel Oxidation Catalyst and a Particulate Filter 2006-01-0266

An experimental and computational study was performed to evaluate the performance of the CRT™ technology with an off-highway engine with a cooled low pressure loop EGR system. The MTU-Filter 1D DPF code predicts the particulate mass evolution (deposition and oxidation) in a diesel particulate filter (DPF) during simultaneous loading and during thermal and NO₂-assisted regeneration conditions. It also predicts the pressure drop across the DPF, the flow and temperature fields, the solid filtration efficiency and the particle number distribution downstream of the DPF. A DOC model was also used to predict the NO₂ upstream of the DPF.

The DPF model was calibrated to experimental data at temperatures from 230°C to 550°C, and volumetric flow rates from 9 to 39 actual m³/min. Model predictions of the solid particulate mass deposited in the DPF after each loading and regeneration case were in agreement within +/-10g (or+/-10%) of experimental measurements at the majority of the engine operating conditions. The activation temperatures (Ea/R = 18000 K for thermal, and 14650 K for NO₂-assisted) obtained from the model calibration are in good agreement with values reported in the literature and gave good results in the model calibration by using constant pre-exponential factors throughout the entire range of conditions evaluated. The average clean filter permeability was 2.372x10^-13 m², which is in the range of permeability values reported in the literature. Estimates of the solid particulate mass packing density inside the porous wall were 1 to 5 kg/m³; and percolation factors were 0.81 to 0.97. Average particulate layer permeability was 1.95x10^-14 m². Solid particulate layer packing density values were between 11 and 128 kg/m³. These values were in good agreement with the Peclet number correlation theory reported in the literature. NO₂-assisted oxidation of PM in the DPF showed experimentally that a significant reduction of the pressure drop can be achieved (<8 kPa) when sufficient NO₂ (>120 ppm) is available and high exhaust gas temperatures (∼360-460-C) can be maintained, even at high PM loadings (low NO₂/solid PM ratios).

The CRT™ (DOC-DPF system) showed limited advantages when used with high PM rates (low NOx/PM ratios) in combination with a low pressure loop EGR strategy for a continuous operation of an engine-exhaust aftertreatment system. The DOC model predicted the conversion of NO to NO₂ within +/-5% of the experimentally measured conversion efficiencies. In a parametric study, the predicted NO₂ concentrations were used as input in the DPF model to estimate the oxidation of solid particulate mass in the filter. Temperature is the most important factor in both, thermal and NO₂-assisted oxidation processes. Higher temperatures require less NO₂ to be used and lower NO₂/PM ratios. NO₂ is much more effective than O₂ in PM oxidation in a DPF. NO₂ flow rates are more important than NO₂/PM ratios.