Numerical Prediction of Particulate Matter (PM) Collection Efficiency, Loading, and Flow Characteristics in Partially Damaged Particulate Filters with Different PM Size Classes

The objective of the current study is to numerically predict the collection efficiency, particulate matter (PM) loading, pressure drop, and flow characteristics in partially damaged or unplugged filters. Five different PM size classes with mean particle diameters ranging from 25 to 300 nm are considered for loading the filter. These PM classes are transported in the computational domain as scalars and collected in the filter through Brownian diffusion and interception mechanisms. Four different partially damaged filters with varying damaged cross-sections in the outlet face of the filter are considered. Five different exhaust gas flow rates from 50 to 300 kg/h with a transient soot loading condition are considered, which leads to different temporal and spatial soot cake evolutions as well as a different total soot mass in the filter. As expected, plugged filter sections have higher filtration efficiencies which increases monotonically with soot accumulation. For damaged segment, however, efficiency is nonmonotonic and depends strongly on particle size, loading, and prevailing flow conditions. The collection efficiency of damaged segments is less than 40% at all flow rates and damaged cross-sections considered in this study. The overall filter efficiency is evaluated as the sum of flow averaged filtration efficiencies of both plugged and unplugged sections. The overall filter efficiency is less than 100% and this efficiency decreases from filter-1 to filter-4 as the damaged filter section contributes to the efficiency loss. Spatial and temporal evolution of soot cake is different in damaged and undamaged sections. Strong nonuniform soot distribution is observed in the partially damaged filters in both the axial and radial direction. One objective of the current study is to analyze the overall filter collection efficiency with respect to the percentage of damage, which as a result will assist in the roadworthiness studies, on-board diagnostic studies, or periodic technical inspection of the filters or damaged filters.