Minimizing Filter Volume by Design Optimization 2007-01-0657
As Diesel Particulate Filter (DPF) applications become widespread, the need for downsizing of filters increases. Indeed, downsizing allows reducing both filter and system costs, facilitates filter integration in the exhaust line close to the engine, and reduces overall system mass and potentially the precious metal loading.
Filter downsizing is mainly limited by filter thermo-mechanical resistance because the system must be capable of storing enough soot before being forced to start filter regeneration in order to limit oil dilution and fuel consumption. The interval between two regenerations depends on filter maximum soot load (MSL) and volume. Thus, it is desired to increase filter MSL in order to keep long regeneration intervals with minimum filter volume. Moreover, in order to maintain acceptable backpressure on a loaded filter, it is required to use optimized cell geometries allowing significant pressure drop reductions.
The current criterion used to define MSL is the appearance of the first crack inside the filter. This criterion is too conservative for recrystallized silicon carbide (RSiC) filters. Indeed, durability and robustness tests performed on RSiC filters show that it is possible to use a higher soot mass than the current MSL without degrading filter functional properties such as filtration efficiency and pressure drop. Therefore, filter downsizing is possible, but it is necessary to reduce filter pressure drop when it is loaded with soot. To do this, cell geometry has been optimized by increasing cell density and reducing wall thickness. Asymmetrical design is also maintained to guarantee good ash storage capacity. This new optimized filter enables a filter volume reduction of 20% while maintaining the same level of performance.