Method and apparatus for gaseous mixing in a diesel exhaust system

Abstract

A mixing device and method for a diesel exhaust system is disclosed having a chamber, a mixer within the chamber, and an injection tube supported on the mixer within the chamber. The mixer is positioned within the chamber adjacent an inlet and includes a plurality of angled blades to effect turbulent flow in a diesel exhaust stream entering the chamber through the inlet. The injection tube includes a plurality of injection points (e.g., openings) for discharging a reagent, such as gaseous ammonia (NH 3 ), into the exhaust stream. The injection tube is curved, and more specifically it is coiled with the injection points spread along the length of the tube in order to deliver reagent across a section of the chamber perpendicular to the exhaust stream flow.

1 . A mixing device for a diesel exhaust system comprising:
 a chamber having an inlet at one end for permitting entrance of an exhaust stream from a diesel engine and an outlet at an opposing end;   a mixer within the chamber adjacent the inlet and positioned to effect turbulent flow in an exhaust stream entering the chamber through the inlet; and   an injection tube supported within the chamber by the mixer.   
     
     
         2 . The mixing device of  claim 1 , wherein the injection tube comprises a plurality of injection points therein for discharging a reagent into the exhaust stream, and extends within a plane of the chamber. 
     
     
         3 . The mixing device of  claim 2 , wherein the injection tube is curved. 
     
     
         4 . The mixing device of  claim 2 , wherein the injection tube is coiled. 
     
     
         5 . The mixing device of  claim 1 , wherein the mixer comprises a plurality of fixed blades angled to deflect the exhaust stream. 
     
     
         6 . The mixing device of  claim 2 , wherein the mixer comprises a plurality of blades angled to impart mixing to the exhaust stream and the injection tube extends across each blade within the chamber. 
     
     
         7 . The mixing device of  claim 1 , wherein the injection tube is connected to the mixer. 
     
     
         8 . The mixing device of  claim 1 , wherein the chamber is positioned between a diesel particulate filter (DPF) and a NO x  slip catalyst canister. 
     
     
         9 . The mixing device of  claim 1 , wherein the chamber is positioned between a diesel oxidation catalyst (DOC) canister and a NO x  particulate filter (NPF) canister. 
     
     
         10 . A mixing device for a diesel exhaust system comprising:
 a chamber having an inlet at one end for permitting entrance of an exhaust stream from a diesel engine and an outlet at an opposing end;   a mixer within the chamber adjacent the inlet; and   an injection tube having a plurality of injection points and extending into the chamber.   
     
     
         11 . The mixing device of  claim 10 , wherein the injection tube is supported by the mixer within the chamber. 
     
     
         12 . The mixing device of  claim 10 , wherein the injection tube is curved. 
     
     
         13 . The mixing device of  claim 12 , wherein the injection tube is coiled. 
     
     
         14 . The mixing device of  claim 10 , wherein the mixer comprises a plurality of fixed blades angled to effect turbulent flow in the exhaust stream. 
     
     
         15 . The mixing device of  claim 11 , wherein the mixer comprises a plurality of blades angled to impart mixing to the exhaust stream and the injection tube extends across each blade within the chamber. 
     
     
         16 . The mixing device of  claim 10 , wherein the injection tube is connected to the mixer. 
     
     
         17 . The mixing device of  claim 10 , wherein the chamber is positioned between a diesel particulate filter (DPF) and a NO x  slip catalyst canister. 
     
     
         18 . The mixing device of  claim 10 , wherein the chamber is positioned between a diesel oxidation catalyst (DOC) canister and a NO x  particulate filter (NPF) canister. 
     
     
         19 . A method for mixing gaseous ammonia in a diesel exhaust system comprising the steps of:
 a. exhausting a diesel exhaust stream from an engine through a conduit in fluid communication with the engine;   b. directing the diesel exhaust stream to flow through the conduit into a housing having a mixer, an injection tube and an exit disposed therein;   c. creating a turbulent flow in the diesel exhaust stream within the housing as the stream passes through the mixer;   d. injecting gaseous NH 3  from the injection tube into the diesel exhaust stream as the stream moves from the mixer toward the housing exit to create a treated exhaust stream; and   e. discharging the treated exhaust stream through the housing exit.   
     
     
         20 . The method of  claim 19 , wherein the mixer comprises a plurality of fixed blades angled to deflect the diesel exhaust stream. 
     
     
         21 . The method of  claim 19 , wherein the injection tube comprises a plurality of injection points for introducing NH 3  gas into the diesel exhaust stream. 
     
     
         22 . The method of  claim 21 , wherein the injection tube is supported in the housing by the mixer. 
     
     
         23 . The method of  claim 21 , wherein the injection tube comprises a coil. 
     
     
         24 . The method of  claim 19 , further comprising the step of creating a homogenous mixture of diesel exhaust and gaseous NH 3 . 
     
     
         25 . The method of  claim 24 , wherein the step of creating a homogenous mixture comprises the step of injecting gaseous NH 3  into the diesel exhaust stream at a plurality of points. 
     
     
         26 . The method of  claim 25 , wherein the injection tube comprises a plurality of injection points spaced throughout a cross-section of the housing. 
     
     
         27 . A method of treating diesel exhaust from an engine in a motor vehicle, the method comprising the steps of:
 a. exhausting a diesel exhaust stream from an engine through a conduit in fluid communication with the engine;   b. directing the diesel exhaust stream to flow through the conduit into a housing having a mixer, an injection tube and an exit disposed therein, wherein the injection tube is in fluid communication with a reagent supply;   c. creating a turbulent flow in the diesel exhaust stream within the housing as the stream passes through the mixer;   d. injecting a gaseous reagent from the reagent supply through the injection tube into the diesel exhaust stream as the stream moves from the mixer toward the housing exit to create a treated exhaust stream; and   e. discharging the treated exhaust stream through the housing exit.