Hydrocarbon scr aftertreatment system

Abstract

An engine exhaust aftertreatment system including a selective catalytic reduction (SCR) device. The system contains no significant amount of catalyzed material upstream of the SCR device.

1 . An engine exhaust aftertreatment system comprising:
 a selective catalytic reduction (SCR) device in an exhaust stream of an engine, the SCR device including a composition that reduces an amount of NOx in the presence of a reductant; and wherein no significant amount of catalyzed material is present in the exhaust stream upstream of the SCR device.   
   
   
       2 . The engine exhaust aftertreatment system of  claim 1  wherein the SCR device is not sensitive to the ratio of NO to NO2 in the exhaust stream. 
   
   
       3 . The engine exhaust aftertreatment system of  claim 1  wherein the composition of the SCR device includes silver tungstate. 
   
   
       4 . The engine exhaust aftertreatment system of  claim 1  wherein the reductant is a hydrocarbon. 
   
   
       5 . The engine exhaust aftertreatment system of  claim 1  further including: a clean-up catalyst downstream of the SCR device. 
   
   
       6 . The engine exhaust aftertreatment system of  claim 1  further including: a diesel particulate filter present in the exhaust stream upstream of the SCR device. 
   
   
       7 . The engine exhaust aftertreatment system of  claim 6  further including: a heat source present in the exhaust stream upstream of the diesel particulate filter. 
   
   
       8 . The engine exhaust aftertreatment system of  claim 7  wherein the heat source is a fuel fired burner. 
   
   
       9 . An engine exhaust aftertreatment system comprising:
 a selective catalytic reduction (SCR) device in an exhaust stream of an engine, the SCR device including a composition that reduces an amount of NOx in the presence of a reductant; and wherein a ratio of NO to NO2 exiting the engine is substantially the same as a ratio of NO to NO2 entering the SCR device.   
   
   
       10 . The engine exhaust aftertreatment system of  claim 9  wherein no significant amount of catalyzed material is present in the exhaust stream upstream of the SCR device. 
   
   
       11 . The engine exhaust aftertreatment system of  claim 9  wherein the SCR device is not sensitive to the ratio of NO to NO2 in the exhaust stream. 
   
   
       12 . The engine exhaust aftertreatment system of  claim 9  wherein the composition of the SCR device includes silver tungstate. 
   
   
       13 . The engine exhaust aftertreatment system of  claim 9  wherein the reductant is a hydrocarbon. 
   
   
       14 . The engine exhaust aftertreatment system of  claim 9  further including: a clean-up catalyst downstream of the SCR device. 
   
   
       15 . The engine exhaust aftertreatment system of  claim 9  further including: a diesel particulate filter present in the exhaust stream upstream of the SCR device. 
   
   
       16 . The engine exhaust aftertreatment system of  claim 15  further including: a heat source present in the exhaust stream upstream of the diesel particulate filter. 
   
   
       17 . The engine exhaust aftertreatment system of  claim 16  wherein the heat source is a fuel fired burner.