Pressure Drop and Cleaning of In-Use Ash Loaded Diesel Particulate Filters

Environmental Protection Agency (EPA) emissions standards for on-road heavy-duty diesel engines in 2007 will require the use of diesel particulate filters (DPF) to reach the regulated limit of 0.01g/bhp-hr for particulate matter. The inorganic portion of the particulate matter, referred to as ash, accumulates in the DPF over time with engine operation and periodic cleaning is necessary to remove the buildup. In anticipation of the required cleaning, flow bench testing and modeling were conducted for heavy-duty diesel DPFs to determine the effectiveness of compressed air nozzle cleaning and water cleaning.

The result from this work shows that the first 10 minutes of cleaning removes greater than 55% of the filter soot/ash. Water cleaning was investigated and shows that it reduces filter pressure drop when repeated air cleaning was incapable of further reducing the pressure drop. Zero-dimensional modeling was demonstrated to be applicable to predict the heavily loaded in-use filters of soot and ash. Two methods of defining a cleaning efficiency were developed with one based on filter pressure drop and another on filter mass. Utilization of an average permeability and inertial coefficient based on filter size to predict the clean pressure drop was insufficient for determining a cleaning efficiency.