Exhaust aftertreatment system having a diesel particulate filter manufactured for reducing thermal gradients

Abstract

A diesel particulate filter includes a honeycomb structure having a plurality of elongated cell walls defining a plurality of passages and a skin layer surrounding the honeycomb structure. The filter is regenerated by oxidizing particulate matter trapped within the honeycomb structure by heating at least a portion of the honeycomb structure. A thermal gradient between the honeycomb structure and the skin layer is limited to less than a crack causing thermal gradient by utilizing at least one of maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5, blocking at least those passages comprising a perimeter of the honeycomb structure, and heating the skin layer from an external side.

1 . A method of regenerating a diesel particulate filter, wherein the diesel particulate filter includes a honeycomb structure having a plurality of elongated cell walls defining a plurality of passages and a skin layer surrounding the honeycomb structure, comprising:
 oxidizing particulate matter trapped within the honeycomb structure by heating at least a portion of the honeycomb structure; and   limiting a thermal gradient between the honeycomb structure and the skin layer to less than a crack causing thermal gradient, wherein the limiting step includes at least one of maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5, blocking at least those passages comprising a perimeter of the honeycomb structure, and heating the skin layer from an external side.   
   
   
       2 . The method of  claim 1 , wherein the limiting step includes maintaining a ratio of the heat capacity of the skin layer to the heat capacity of the cell walls at less than about 2.5. 
   
   
       3 . The method of  claim 2 , wherein the limiting step further includes limiting a thickness of the skin layer to less than about 0.5 mm. 
   
   
       4 . The method of  claim 1 , wherein the limiting step includes at least two of maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5, blocking at least those passages comprising a perimeter of the honeycomb structure, and heating the skin layer from an external side. 
   
   
       5 . The method of  claim 1 , wherein the limiting step includes maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5 and blocking at least those passages comprising a perimeter of the honeycomb structure. 
   
   
       6 . The method of  claim 5 , wherein the limiting step further includes maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 2.5. 
   
   
       7 . The method of  claim 6 , wherein the limiting step further includes limiting a thickness of the skin layer to less than about 0.5 mm. 
   
   
       8 . An exhaust aftertreatment system, comprising:
 a can having a gas inlet and a gas outlet;   a substrate having a honeycomb structure and a skin layer surrounding the honeycomb structure disposed within the can, the honeycomb structure comprising a plurality of elongated cell walls extending from the gas inlet to the gas outlet and defining a plurality of passages, wherein the cell walls are permeable relative to the skin layer; and   means for limiting a thermal gradient between the honeycomb structure and the skin layer to less than a crack causing thermal gradient during a regeneration process, wherein the limiting means include at least one of means for maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5, means for blocking at least those passages comprising a perimeter of the honeycomb structure, and means for heating the skin layer from an external side.   
   
   
       9 . The exhaust aftertreatment system of  claim 8 , wherein the limiting means include means for maintaining a ratio of the heat capacity of the skin layer to the heat capacity of the cell walls at less than about 2.5. 
   
   
       10 . The exhaust aftertreatment system of  claim 9 , wherein the cell walls and the skin layer comprise a ceramic material. 
   
   
       11 . The exhaust aftertreatment system of  claim 10 , wherein the maintaining means include limiting a thickness of the skin layer to less than about 0.5 mm. 
   
   
       12 . The exhaust aftertreatment system of  claim 8 , wherein the limiting means include at least two of means for maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5, means for blocking at least those passages comprising a perimeter of the honeycomb structure, and means for heating the skin layer from an external side. 
   
   
       13 . The exhaust aftertreatment system of  claim 8 , wherein the limiting means include maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 5 and blocking at least those passages comprising a perimeter of the honeycomb structure. 
   
   
       14 . The exhaust aftertreatment system of  claim 13 , wherein the limiting means further include maintaining a ratio of a heat capacity of the skin layer to a heat capacity of the cell walls at less than about 2.5. 
   
   
       15 . The exhaust aftertreatment system of  claim 14 , wherein the limiting means further include limiting a thickness of the skin layer to less than about 0.5 mm. 
   
   
       16 . A diesel particulate filter, comprising:
 a honeycomb structure having a plurality of elongated cell walls defining a plurality of passages;   a skin layer surrounding the honeycomb structure;   at least one crack avoidance feature of: the skin layer having a heat capacity less than about five times the heat capacity of the cell walls and at least those passages comprising a perimeter of the honeycomb structure being blocked; and   wherein the crack avoidance feature limits a thermal gradient between the honeycomb structure and the skin layer to less than a crack causing thermal gradient.   
   
   
       17 . The diesel particulate filter of  claim 16 , wherein the cell walls and the skin layer comprise a ceramic material. 
   
   
       18 . The diesel particulate filter of  claim 17 , wherein the crack avoidance feature includes the skin layer having a thickness of less than about 0.5 mm.