Exhaust treatment system with an oxidation device for NO2 control

Abstract

An exhaust treatment system includes an oxidation device having a plurality of channels through which a flow of exhaust flows. A first portion of the channels of the oxidation device are coated with catalytic material for converting NO to NO 2 and a second portion of the channels are uncoated with the catalytic material. The exhaust treatment system also includes a selective catalytic reduction device disposed downstream from the oxidation device. The selective catalytic reduction device is configured to receive the flow of exhaust passing through the oxidation device.

1 . An exhaust treatment system comprising:
 an oxidation device having a plurality of channels through which a flow of exhaust flows, a first portion of the channels being coated with catalytic material for converting NO to NO 2 , a second portion of the channels being uncoated with the catalytic material; and   a selective catalytic reduction device disposed downstream from the oxidation device, the selective catalytic reduction device being configured to receive the flow of exhaust passing through the oxidation device.   
   
   
       2 . The exhaust treatment system of  claim 1 , wherein a percentage of the channels of the oxidation device that are coated with the catalytic material is based on a target NO:NO 2  ratio in the flow of exhaust supplied to the selective catalytic reduction device. 
   
   
       3 . The exhaust treatment system of  claim 2 , wherein the target NO:NO 2  ratio in the flow of exhaust supplied to the selective catalytic reduction device is approximately 50:50. 
   
   
       4 . The exhaust treatment system of  claim 2 , wherein the percentage of channels coated in the oxidation device is determined when operating at a predetermined operating condition when the target NO:NO 2  ratio is achieved, the predetermined operating condition including at least one of a predetermined mass flow and a predetermined temperature. 
   
   
       5 . The exhaust treatment system of  claim 1 , wherein the first portion of the channels of the oxidation device that are coated with the catalytic material constitute approximately 75% of the channels of oxidation device. 
   
   
       6 . The exhaust treatment system of  claim 1 , further including a particulate filter downstream from the oxidation device. 
   
   
       7 . The exhaust treatment system of  claim 1 , wherein the selective catalytic reduction device is a downstream selective catalytic reduction device, and the exhaust treatment system further includes:
 an upstream selective catalytic reduction device disposed upstream from the oxidation device; and   an upstream injector disposed upstream from the upstream selective catalytic reduction device, the upstream injector configured to inject reductant into the flow of exhaust.   
   
   
       8 . The exhaust treatment system of  claim 7 , wherein the oxidation device is a downstream oxidation device, and the exhaust treatment system further includes:
 an upstream oxidation device disposed upstream from the upstream selective catalytic reduction device, the upstream oxidation device having a plurality of channels through which the flow of exhaust flows, and a percentage less than 100% of the channels of the upstream oxidation catalyst are coated with the catalytic material.   
   
   
       9 . The exhaust treatment system of  claim 8 , further including:
 a sensor for sensing a characteristic of the flow of exhaust upstream from the downstream selective catalytic reduction device and downstream from the upstream selective catalytic reduction device; and   a controller connected to the sensor, the controller being configured to receive the sensed characteristic and control an injection of reductant by the upstream injector based on the sensed characteristic.   
   
   
       10 . The exhaust treatment system of  claim 9 , wherein the characteristic is a NO:NO 2  ratio. 
   
   
       11 . The exhaust treatment system of  claim 8 , wherein the percentage of coated channels in the downstream oxidation device is greater than 50%, and the percentage of coated channels in the upstream oxidation device is less than 50%. 
   
   
       12 . The exhaust treatment system of  claim 1 , further including a first passageway configured to direct a portion of the flow of exhaust around the oxidation device, the oxidation device being disposed in a second passageway. 
   
   
       13 . The exhaust treatment system of  claim 12 , further including:
 a first particulate filter disposed in the first passageway; and   a second particulate filter disposed in the second passageway.   
   
   
       14 . The exhaust treatment system of  claim 13 , wherein at least one of the particulate filters is coated with the catalytic material for converting NO to NO 2 . 
   
   
       15 . The exhaust treatment system of  claim 13 , wherein at least one of the particulate filters is a flow through type filter. 
   
   
       16 . The exhaust treatment system of  claim 12 , wherein the oxidation device is a second oxidation device, and the exhaust treatment system further includes a first oxidation device in the first passageway, the first oxidation device having a plurality of channels through which the flow of exhaust flows, a percentage less than 100% of the channels of the first oxidation device being coated with the catalytic material. 
   
   
       17 . The exhaust treatment system of  claim 16 , wherein:
 the selective catalytic reduction device is a downstream selective catalytic reduction device disposed downstream from the first and second passageways; and   the exhaust treatment system further includes:
 a first selective catalytic reduction device in the first passageway downstream from the first oxidation device; and 
 a second selective catalytic reduction device in the second passageway downstream from the second oxidation device. 
   
   
   
       18 . The exhaust treatment system of  claim 17 , wherein the percentage of channels coated with the catalytic material in the first oxidation device is greater than 50%, and the percentage of channels coated with the catalytic material in the second oxidation device is less than 50%. 
   
   
       19 . The exhaust treatment system of  claim 17 , further including:
 a first particulate filter in the first passageway downstream from the first selective catalytic reduction device; and   a second particulate filter in the second passageway downstream from the second selective catalytic reduction device.   
   
   
       20 . The exhaust treatment system of  claim 1 , wherein the catalytic material is platinum. 
   
   
       21 . A method for treating a flow of exhaust comprising:
 generating the flow of exhaust;   passing the flow of exhaust through a plurality of channels of a downstream oxidation device, a first portion of the channels being coated with catalytic material for converting NO to NO 2 , a second portion of the channels being uncoated with the catalytic material; and   directing the combined flow of exhaust to a downstream selective catalytic reduction device disposed downstream from the downstream oxidation device.   
   
   
       22 . The method of  claim 21 , further including:
 passing the flow of exhaust through a plurality of channels of an upstream oxidation device disposed upstream from the downstream oxidation device, a first portion of the channels of the upstream oxidation device being coated with the catalytic material, a second portion of the channels of the channels of the upstream oxidation device being uncoated with the catalytic material;   injecting reductant with an upstream injector disposed downstream from the upstream oxidation device and upstream from the downstream oxidation device; and   passing the flow of exhaust through an upstream selective catalytic reduction device disposed upstream from the downstream oxidation device and downstream from the upstream injector.   
   
   
       23 . The method of  claim 22 , further including:
 sensing a characteristic of the flow of exhaust; and   controlling the injection of reductant by the upstream injector based on the sensed characteristic.   
   
   
       24 . The method of  claim 23 , wherein the sensed characteristic is a sensed NO:NO 2  ratio in the flow of exhaust. 
   
   
       25 . The method of  claim 24 , wherein the injection of reductant by the upstream injector is controlled based on a target NO:NO 2  ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device. 
   
   
       26 . The method of  claim 25 , wherein the target NO:NO 2  ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device is approximately 50:50. 
   
   
       27 . An exhaust treatment system comprising:
 an upstream oxidation device having a plurality of channels through which a flow of exhaust flows, a first portion of the channels being coated with catalytic material for converting NO to NO 2 , a second portion of the channels being uncoated with the catalytic material;   an upstream injector configured to inject reductant into the flow of exhaust upstream from the upstream selective catalytic reduction device;   an upstream selective catalytic reduction device disposed downstream from the upstream injector, the upstream selective catalytic reduction device being configured to receive the flow of exhaust;   a downstream oxidation device disposed downstream from the upstream selective catalytic reduction device, the downstream oxidation device having a plurality of channels through which the flow of exhaust flows, a first portion of the channels of the downstream oxidation device being coated with the catalytic material, a second portion of the channels of the downstream oxidation device being uncoated with the catalytic material; and   a downstream selective catalytic reduction device disposed downstream from the downstream oxidation device, the downstream selective catalytic reduction device being configured to receive the flow of exhaust.   
   
   
       28 . The exhaust treatment system of  claim 27 , further including:
 a sensor configured to sense a characteristic of the flow of exhaust; and   a controller connected to the sensor, the controller being configured to receive the sensed characteristic and control an injection of reductant by the upstream injector based on the sensed characteristic.   
   
   
       29 . The exhaust treatment system of  claim 28 , wherein the sensed characteristic is a sensed NO:NO 2  ratio in the flow of exhaust. 
   
   
       30 . The exhaust treatment system of  claim 29 , wherein the controller controls the injection of reductant based on a target NO:NO 2  ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device. 
   
   
       31 . The exhaust treatment system of  claim 30 , wherein the target NO:NO 2  ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device is approximately 50:50.