Adjusting nitrogen oxide ratios in exhaust gas

Abstract

A method of adjusting a ratio of NO to NO 2 in a flow of exhaust gas is disclosed. The method includes directing a first portion of the exhaust flow through at least one first channel, wherein the at least one first channel is a wall-flow channel, and directing a second portion of the exhaust flow through at least one second channel, wherein the at least one second channel is an open flow-through channel. The method further includes converting NO into NO 2 at a first rate in the first portion of the exhaust flow as the first portion of the exhaust flow passes through the at least one first channel and converting NO into NO 2 at a second rate in the second portion of the exhaust flow as the second portion of the exhaust flow passes through the at least one second channel, the second rate being slower than the first rate.

1 . A method of adjusting a ratio of NO to NO 2  in a flow of exhaust gas, the method comprising:
 directing a first portion of the exhaust flow through at least one first channel, wherein the at least one first channel is a wall-flow channel;   directing a second portion of the exhaust flow through at least one second channel, wherein the at least one second channel is an open flow-through channel;   converting NO into NO 2  at a first rate in the first portion of the exhaust flow as the first portion of the exhaust flow passes through the at least one first channel;   converting NO into NO 2  at a second rate in the second portion of the exhaust flow as the second portion of the exhaust flow passes through the at least one second channel, the second rate being slower than the first rate; and   removing particulate matter from the first portion of the exhaust flow as the first portion of the exhaust flow passes through the at least one first channel.   
   
   
       2 . The method of  claim 1 , wherein the first and second rates are selected to provide a final ratio of NO to NO 2  of about 1:1 in the exhaust flow. 
   
   
       3 . The method of  claim 1 , further comprising converting hydrocarbons in one or both of the first and second portions of the exhaust flow as the first and second portions of the exhaust flow pass through the at least one first channel and the at least one second channel, respectively. 
   
   
       4 . The method of  claim 1 , wherein NO is converted into NO 2  at the first rate in the first portion of the exhaust flow using a platinum catalyst, and NO is converted into NO 2  at the second rate in the second portion of the exhaust flow using a palladium catalyst. 
   
   
       5 . The method of  claim 1 , wherein particulate matter is removed from the first portion of the exhaust flow using a plurality of porous filter walls. 
   
   
       6 . A method of altering a composition of exhaust gas flow including particulate matter, hydrocarbons, and NO, the method comprising:
 directing a first portion of the exhaust flow through at least one first channel, wherein the at least one first channel is a wall-flow channel;   directing a second portion of the exhaust flow through at least one second channel, wherein the at least one second channel is an open flow-through channel;   converting NO into NO 2  in the first portion of the exhaust flow as the first portion of the exhaust flow passes through the at least one first channel;   trapping the particulate matter in the first portion of the exhaust flow as the first portion of the exhaust flow passes through the at least one first channel; and   passively regenerating the particulate matter in the second portion of exhaust flow as the second portion of exhaust flow passes from a first end of the at least one second flow channel through a second end of the at least one second flow channel.   
   
   
       7 . The method of  claim 6 , further comprising converting hydrocarbons in one or both of the first and second portions of the exhaust flow as the first and second portions of the exhaust flow pass through the at least one first channel and the at least one second channel, respectively. 
   
   
       8 . The method of  claim 6 , further comprising controlling the amount of particulate matter trapped and passively regenerated to provide a desired amount of particulate matter reduction in the exhaust flow. 
   
   
       9 . The method of  claim 6 , further comprising converting NO into NO 2  at a second rate in the second portion of the exhaust flow as the second portion of the exhaust flow passes through the at least one second channel;
 wherein the second rate is slower than the first rate, and the first and second rates are selected to provide a final ratio of NO to NO 2  of about 1:1 in the exhaust flow.   
   
   
       10 . The method of  claim 6 , wherein particulate matter is trapped in the at least one first channel using a plurality of porous filter walls. 
   
   
       11 . An exhaust filter, comprising:
 at least one first channel configured to convert NO in an exhaust flow to NO 2  at a first rate, the at least one first channel being a wall-flow channel configured to remove particulate matter from the exhaust flow; and   at least one second channel configured to convert NO in an exhaust flow to NO 2  at a second rate, slower than the first rate, wherein the at least one second channel is an open flow-through channel.   
   
   
       12 . The exhaust filter of  claim 11 , further including a plurality of the at least one first and second channels, wherein a ratio of first channels to second channels is configured to provide a final ratio of NO to NO 2  of about 1:1. 
   
   
       13 . The exhaust filter of  claim 11 , wherein the at least one first channel is coated with a platinum catalyst and the at least one second channel is coated with a palladium catalyst. 
   
   
       14 . The exhaust filter of  claim 11 , wherein the at least one first channel includes a plurality of wall-flow channels and the at least one second channel includes a plurality of open flow-through channels. 
   
   
       15 . A method of adjusting a ratio of NO to NO 2  in a flow of exhaust gas, the method comprising:
 directing a first portion of the exhaust flow through at least one first channel, wherein the at least one first channel is a wall-flow channel;   directing a second portion of the exhaust flow through at least one second channel, wherein the at least one second channel is an open flow-through channel;   transforming NO into NO 2  in the first portion of the exhaust flow to yield a first ratio of NO to NO 2 ;   transforming NO into NO 2  in the second portion of the exhaust flow to yield a second ratio of NO to NO 2 ; and   combining the first and second portions of the exhaust flow as the first and second portions of the exhaust flow exit the at least one first and second flow channels to yield a final ratio of NO to NO 2  of about 1:1 in the combined exhaust flow.   
   
   
       16 . The method of  claim 15 , further comprising:
 trapping particulate matter in the at least one first channel to reduce the amount of particulate matter by a first percentage; and passively regenerating particulate matter in the exhaust flow in the at least one second channel to reduce the amount of particulate matter by a second percentage, wherein the first percentage is higher than the second percentage.   
   
   
       17 . The method of  claim 15 , wherein the at least one first channel includes a plurality of wall-flow channels and the at least one second channel includes a plurality of open flow-through channels. 
   
   
       18 . The method of  claim 15 , wherein NO is transformed into NO 2  in the first portion of the exhaust flow using a platinum catalyst and NO is transformed into NO 2  in the second portion of the exhaust flow using a palladium catalyst. 
   
   
       19 . The method of  claim 15 , wherein the first portion includes about 70% to 95% of the exhaust flow and the second portion includes about 5% to 30% of the exhaust flow. 
   
   
       20 . The method of  claim 15 , wherein NO is transformed into NO 2  in the first portion at a faster rate than in the second portion and wherein particulate matter is trapped in the first portion at a higher rate than in the second portion.