Exhaust aftertreatment system with in-elbow reductant injection

Abstract

An exhaust aftertreatment system, such as for a diesel engine, includes a reductant dosing system with an injector positioned in an elbow pipe of an exhaust conduit. A tubeless mixer is positioned in the exhaust conduit between the injector nozzle outlet and an SCR catalyst. The tubeless mixer includes a plurality of rings, all of which are distributed with increasing size as distance from the nozzle outlet increases. The tubeless mixer aides in more uniformly distributing reductant in the exhaust flow prior to arrival at the SCR catalyst.

What is claimed is: 
     
         1 . An exhaust aftertreatment system comprising:
 an exhaust conduit with an elbow pipe positioned between an engine end and a tailpipe end;   an SCR catalyst positioned in the exhaust conduit between the elbow pipe and the tailpipe end;   a reductant dosing system with a nozzle outlet of an injector positioned in the elbow pipe of the exhaust conduit;   a tubeless mixer positioned in the exhaust conduit between the nozzle outlet and the SCR catalyst; and   the tubeless mixer includes a plurality of rings, all of which are distributed with increasing size as distance from the nozzle outlet increases.   
     
     
         2 . The exhaust aftertreatment system of  claim 1  wherein the rings share a common centerline. 
     
     
         3 . The exhaust aftertreatment system of  claim 2  wherein the exhaust conduit immediately adjacent the elbow pipe shares the common centerline. 
     
     
         4 . The exhaust aftertreatment system of  claim 3  wherein leading edges of consecutively increased size rings are located at distances that increase along the common centerline from the nozzle outlet. 
     
     
         5 . The exhaust aftertreatment system of  claim 4  wherein trailing edges of consecutively increased size rings are located at distances that increase along the common centerline from the nozzle outlet. 
     
     
         6 . An elbow pipe of an exhaust conduit comprising:
 a pipe with an inlet and an outlet;   a centerline of the inlet being angled, at an angle greater than zero, with respect to a centerline of the outlet;   the pipe defining an injector opening therethrough;   a tubeless mixer attached to an inner surface of the pipe and including a plurality of rings, all of which are distributed with increasing size as distance from the injector opening increases.   
     
     
         7 . The elbow pipe of  claim 6  wherein the rings share a common centerline. 
     
     
         8 . The elbow pipe of  claim 7  wherein the outlet of the pipe shares the common centerline. 
     
     
         9 . The elbow pipe of  claim 8  wherein leading edges of consecutively increased size rings are located at distances that increase along the common centerline from the injector opening. 
     
     
         10 . The elbow pipe of  claim 9  wherein trailing edges of consecutively increased size rings are located at distances that increase along the common centerline from the injector opening. 
     
     
         11 . The elbow pipe of  claim 10  wherein each of the rings has a circular cross section. 
     
     
         12 . The elbow pipe of  claim 11  wherein the plurality of rings includes five rings. 
     
     
         13 . A method of operating an exhaust aftertreatment system, comprising the steps of:
 moving exhaust in an exhaust conduit from an engine end toward a tailpipe end;   injecting reductant from an injector into an elbow pipe of the exhaust conduit;   mixing the reductant with the exhaust at least in part by passing the exhaust and the reductant through a tubeless mixer that includes a plurality of rings distributed with increasing size as a distance from the injector increases;   reacting NOx in the exhaust with the reductant at an SCR catalyst positioned in the exhaust conduit.   
     
     
         14 . The method of  claim 13  wherein the mixing step includes:
 dispersing the reductant toward an inside wall of the elbow pipe responsive to an exhaust flow being high; and 
 inhibiting impingement of the reductant on the inside wall responsive to the exhaust flow being low. 
 
     
     
         15 . The method of  claim 14  wherein the mixing step includes orienting the rings to share a common centerline. 
     
     
         16 . The method of  claim 15  wherein the mixing step includes orienting the common centerline colinear with a centerline of the exhaust conduit immediately adjacent the elbow pipe.