Exhaust system implementing dual stage SCR

Abstract

An exhaust system for use with an engine is disclosed. The exhaust system may have a passageway, a flow control device situated to feed reductant into the passageway, and a particulate collection device located in fluid communication with the passageway downstream of the flow control device. The particulate collection device may be catalyzed to promote NO X reduction in a presence of the reductant. The exhaust system may also have a reduction device located in fluid communication with the passageway downstream of the flow control device. The reduction device may be catalyzed to promote NO X reduction in a presence of the reductant, and the particulate collection device and the reduction device may receive reductant from only the flow control device.

1 . An exhaust system, comprising:
 a passageway;   a flow control device situated to feed reductant into the passageway;   a particulate collection device located in fluid communication with the passageway downstream of the flow control device, the particulate collection device being catalyzed to promote NO X  reduction in a presence of the reductant; and   a reduction device located in fluid communication with the passageway downstream of the flow control device, the reduction device being catalyzed to promote NO X  reduction in a presence of the reductant,   wherein the particulate collection device and the reduction device receive reductant from only the flow control device.   
   
   
       2 . The exhaust system of  claim 1 , wherein the flow control device is a control valve. 
   
   
       3 . The exhaust system of  claim 1 , wherein the reduction device is located to receive residual reductant passing through the particulate collection device. 
   
   
       4 . The exhaust system of  claim 3 , wherein an effective volume of the particulate collection device is greater than an effective volume of the reduction device. 
   
   
       5 . The exhaust system of  claim 4 , wherein the effective volume of the particulate collection device is about 1.3-2.6 times a displacement volume of an associated engine from which the passageway receives exhaust. 
   
   
       6 . The exhaust system of  claim 5 , wherein the effective volume of the reduction device is about 1.1-2.2 times the displacement volume of the associated engine. 
   
   
       7 . The exhaust system of  claim 1 , wherein a catalyst utilized within the particulate collection device to promote NO X  reduction is different from a catalyst utilized within the reduction device to promote NO X  reduction. 
   
   
       8 . The exhaust system of  claim 7 , wherein the catalyst utilized within the particulate collection device is one of vanadia or zeolite that incorporates copper or iron. 
   
   
       9 . The exhaust system of  claim 7 , wherein the catalyst utilized within the reduction device is one of vanadia or zeolite that incorporates copper or iron. 
   
   
       10 . The exhaust system of  claim 1 , wherein the particulate collection device consumes a greater amount of reductant than the reduction device. 
   
   
       11 . The exhaust system of  claim 10 , wherein the particulate collection device consumes about 60-90% of the reductant. 
   
   
       12 . The exhaust system of  claim 11 , wherein the reduction device consumes about 10-40% of the reductant. 
   
   
       13 . The exhaust system of  claim 1 , wherein the particulate collection device promotes a greater NO X  reduction than the reduction device. 
   
   
       14 . The exhaust system of  claim 13 , wherein the particulate collection device promotes a NO X  reduction of about 45-90%. 
   
   
       15 . The exhaust system of  claim 14 , wherein the reduction device promotes a NO X  reduction of about 10-55%. 
   
   
       16 . The exhaust system of  claim 1 , wherein the reductant is gaseous ammonia. 
   
   
       17 . The exhaust system of  claim 16 , further including a reductant supply in fluid communication with the flow control device, wherein the reductant supply consists of pressurized ammonia gas, liquefied anhydrous ammonia, ammonium carbonate, or ammine salt. 
   
   
       18 . An exhaust system, comprising:
 a first substrate catalyzed to promote NO X  reduction;   a second substrate catalyzed to promote NO X  reduction;   a supply of gaseous ammonia; and   a flow control device situated to feed the gaseous ammonia to the first and second substrates.   
   
   
       19 . The exhaust system of  claim 18 , wherein the first and second substrates are fluidly connected in series and receive all gaseous ammonia from the flow control device. 
   
   
       20 . A power system, comprising:
 a combustion engine;   a passageway connected to receive exhaust from the combustion engine;   a flow control device situated to feed gaseous ammonia into the passageway;   a particulate filter located in fluid communication with the passageway downstream of the flow control device, the particulate filter having a substrate catalyzed to promote NO X  reduction in a presence of the gaseous ammonia; and   an SCR device located in fluid communication with the passageway downstream of the flow control device and the particulate filter, the SCR device having a substrate catalyzed to promote NO X  reduction in a presence of the gaseous ammonia,   wherein the particulate filter and the SCR device receive gaseous ammonia from only the flow control device.