Thermal Durability of a Ceramic Wall-Flow Diesel Filter for Light Duty Vehicles

The thermal durability of a large frontal area cordierite ceramic wall-flow filter for light-duty diesel engine is examined under various regeneration conditions. The radial temperature distribution during burner regeneration, obtained by eight different thermocouples at six different axial sections of a 75″ diameter x 8″ long filter, is used together with physical properties of the filter to compute thermal stresses via finite element analysis. The stress-time history of the filter is then compared with the strength and fatigue characteristics of extruded cordierite ceramic monolith. The successful performance of the filter over as many as 1000 regenerations is attributed to three important design parameters, namely unique filter properties, controlled regeneration conditions, and optimum packaging design. The latter induces significant radial and axial compression in the filter thereby enhancing its strength and reducing the operating stresses. The filter properties are measured for both the new and aged filters following 1000 successful regenerations. It is found that the elastic properties of the filter are modified appreciably with successive regenerations due, possibly, to uniform and homogeneous microcracking. The resulting stresses, under identical temperature profile, are reduced by 50 to 55% thereby promoting filter durability.

The thermal stress data are also compared with the fatigue properties of ceramic filter to assess cumulative damage and to identify packaging designs and regeneration conditions which will help promote filter durability to the required 120K vehicle miles.