Exhaust gas treatment system with improved low temperature performance

Abstract

An exhaust gas treatment system for an internal combustion engine with an exhaust gas pathway configured to receive exhaust gas from the internal combustion engine. The system includes a heater operable to heat the exhaust gas as it passes through the exhaust gas pathway, an injector configured to inject reductant into the exhaust gas pathway, a first treatment element positioned in the exhaust gas pathway downstream of the heater and the injector, and a second treatment element positioned in the exhaust gas pathway downstream of the first treatment element. At least one of the first treatment element or the second treatment element includes a selective catalytic reduction (SCR) element, and the exhaust gas treatment system does not include a precious metal catalyst upstream of the first treatment element.

What is claimed is: 
     
         1 . An exhaust gas treatment system for an internal combustion engine, the system comprising:
 an exhaust gas pathway configured to receive exhaust gas from the internal combustion engine;   a heater operable to heat the exhaust gas as it passes through the exhaust gas pathway;   an injector configured to inject reductant into the exhaust gas pathway;   a first treatment element positioned in the exhaust gas pathway downstream of the heater and the injector; and   a second treatment element positioned in the exhaust gas pathway downstream of the first treatment element,   wherein at least one of the first treatment element or the second treatment element includes a selective catalytic reduction (SCR) element, and   wherein the exhaust gas treatment system does not include a precious metal catalyst upstream of the first treatment element.   
     
     
         2 . The exhaust gas treatment system of  claim 1 , wherein the second treatment element includes a combined selective catalytic reduction and diesel particulate filter (SCR+F) element. 
     
     
         3 . The exhaust gas treatment system of  claim 1 , wherein the first treatment element includes a combined selective catalytic reduction and diesel particulate filter (SCR+F) element. 
     
     
         4 . The exhaust gas treatment system of  claim 1 , wherein the first treatment element includes a diesel particulate filter (DPF). 
     
     
         5 . The exhaust gas treatment system of  claim 1 , wherein the second treatment element includes an ammonia oxidation catalyst (AOC). 
     
     
         6 . The exhaust gas treatment system of  claim 1 , wherein the heater includes a fuel burner. 
     
     
         7 . The exhaust gas treatment system of  claim 1 , wherein the heater includes an electric heating element. 
     
     
         8 . The exhaust gas treatment system of  claim 1 , wherein the heater is operable to heat the exhaust gas to a temperature of at least 550 degrees Celsius. 
     
     
         9 . An exhaust gas treatment system for an internal combustion engine, the system comprising:
 an exhaust gas pathway configured to receive exhaust gas from the internal combustion engine;   an ozone injector configured to inject ozone into the exhaust gas pathway;   a selective catalytic reduction (SCR) element positioned in the exhaust gas pathway downstream of the ozone injector; and   a particulate filter positioned in the exhaust gas pathway downstream of the ozone injector such that ozone from the ozone injector can oxidize soot thereon.   
     
     
         10 . The exhaust gas treatment system of  claim 9 , wherein the exhaust gas treatment system does not include a precious metal catalyst upstream of the particulate filter. 
     
     
         11 . The exhaust gas treatment system of  claim 9 , wherein the SCR element includes a vanadium-based catalyst. 
     
     
         12 . The exhaust gas treatment system of  claim 9 , wherein the ozone from the ozone injector is configured to oxidize soot on the particulate filter at temperatures less than 600 degrees Celsius. 
     
     
         13 . The exhaust gas treatment system of  claim 9 , further comprising an ammonia oxidation catalyst (AOC) disposed downstream of the SCR element. 
     
     
         14 . The exhaust gas treatment system of  claim 9 , wherein the particulate filter is part of a combined selective catalytic reduction and diesel particulate filter (SCR+F) element. 
     
     
         15 . The exhaust gas treatment system of  claim 9 , further comprising an ozone generator configured to supply ozone to the ozone injector; and a transfer line fluidly coupled to the ozone generator, wherein the transfer line is configured to supply ozone to an air intake of the internal combustion engine. 
     
     
         16 . The exhaust gas treatment system of  claim 9 , further comprising a reductant injector configured to inject reductant into the exhaust gas pathway downstream of the ozone injector. 
     
     
         17 . A method of treating exhaust gas from an internal combustion engine as the exhaust gas passes through an exhaust gas pathway, the method comprising:
 injecting reductant into the exhaust gas pathway with a reductant injector;   filtering particulate matter from the exhaust gas with a first treatment element located downstream of the reductant injector;   oxidizing soot on the first treatment element with ozone; and converting nitrogen oxides (NO x ) from the exhaust gas with a second treatment element located downstream of the reductant injector.   
     
     
         18 . The method of  claim 17 , wherein the first treatment element includes a combined selective catalytic reduction and diesel particulate filter (SCR+F) element. 
     
     
         19 . The method of  claim 18 , wherein the first treatment element is located upstream of the second treatment element. 
     
     
         20 . The method of  claim 18 , further comprising generating ozone with an ozone generator, wherein oxidizing soot on the first treatment element with ozone includes injecting ozone from the ozone generator into the exhaust gas pathway; and
 supplying ozone from the ozone generator into an air intake of the internal combustion engine.