Methods and apparatus for injecting atomized fluid

Abstract

The present invention provides methods and apparatus for injecting fluid, such as an aqueous urea solution, into an exhaust stream in order to reduce oxides of nitrogen (NOx) emissions from diesel engine exhaust The present invention uses mechanical spill return atomization techniques to produce droplets approximately 50 μm SMD (Sauter mean diameter) or smaller. This size range is appropriate to allow urea to react into ammonia within the residence time associated with an on-road diesel engine. This effect is achieved through the use of a whirl plate having a plurality of whirl slots surrounding an exit orifice of the injector, which produce a high velocity rotating flow in the whirl chamber. When the rotating flow of fluid is passed through the exit orifice into an exhaust stream, atomization occurs from a combination of centrifugal force and shearing of the fluid by air as it jets into the exhaust stream.

1 . A method of injecting atomized reagent into an exhaust gas stream at low pressure, comprising: 
 introducing a reagent into an injector body;    providing a predetermined pressure setpoint for pressurizing said reagent in said injector body, said predetermined pressure setpoint being variable within a range of approximately 60 to 80 pounds per square inch;    imparting a high velocity rotating flow to at least a portion of the pressurized reagent within a whirl chamber of said injector body, said whirl chamber having a plurality of whirl slots; and    metering a precise amount of atomized reagent from an exit orifice into said exhaust gas stream.    
     
     
         2 . A method in accordance with  claim 1 , furthering comprising: 
 circulating reagent maintained in said injector body through said injector body to enable at least one of: (a) maintaining of said reagent within a desired temperature range; and (b) maintaining of said injector within a desired temperature range.    
     
     
         3 . A method in accordance with  claim 2 , wherein a flow rate of said reagent circulating through said injector body is variable from approximately 2 to 15 gallons per hour.  
     
     
         4 . A method in accordance with  claim 2 , wherein said desired temperature range for said reagent comprises 5° C. to 85° C.  
     
     
         5 . A method in accordance with  claim 1 , wherein the reagent comprises a urea solution.  
     
     
         6 . A method in accordance with  claim 1 , wherein said reagent comprises a hydrocarbon.  
     
     
         7 . A method in accordance with  claim 1 , wherein said exhaust gas stream comprises a diesel engine exhaust stream.  
     
     
         8 . A method in accordance with  claim 1 , wherein said predetermined pressure setpoint is variable to provide at least one of increased operating range and varied spray patterns.  
     
     
         9 . A method in accordance with  claim 1 , wherein varying said predetermined pressure setpoint varies an average droplet size of said atomized reagent metered into said exhaust gas stream.  
     
     
         10 . A method in accordance with  claim 9 , wherein said average droplet size is within a range of approximately 40 to 60 μm SMD.  
     
     
         11 . A method in accordance with  claim 1 , wherein varying said predetermined pressure setpoint varies a flow rate of said atomized reagent metered into said exhaust gas stream.  
     
     
         12 . A method in accordance with  claim 11 , wherein said flow rate of said atomized reagent metered into said exhaust gas stream is in a range of approximately 3 to 500 grams per minute.  
     
     
         13 . A method in accordance with  claim 11 , wherein varying the flow rate further varies at least one of: (1) a droplet size of said atomized reagent metered into said exhaust gas stream; and (2) an amount of cooling provided by circulating reagent remaining in the injector body through the injector body.  
     
     
         14 . A method in accordance with  claim 1 , wherein said plurality of whirl slots comprises at least four whirl slots.  
     
     
         15 . A method in accordance with  claim 1 , wherein: 
 said whirl chamber is provided in a whirl plate; and    said whirl plate is removable from said injector body.    
     
     
         16 . A method in accordance with  claim 15 , wherein different whirl plates with correspondingly different characteristics can be interchanged in said injector body for different applications of said injector.  
     
     
         17 . A method in accordance with  claim 16 , wherein said different whirl plates provide different spray patterns of said atomized reagent metered into said exhaust gas stream.  
     
     
         18 . A method in accordance with  claim 16 , wherein said different characteristics of said different whirl plates comprise at least one of a different number of whirl slots, whirl slots of different length, whirl slots of different width, whirl slots of different depth, a differently sized whirl chamber, and a differently sized exit orifice.  
     
     
         19 . A method in accordance with  claim 1 , further comprising: 
 providing a metering plug arranged within a lower section of said injector body; and    controlling the metering of said reagent into said exhaust gas stream via movement of the metering plug from between an open position opening said exit orifice and a closed position closing said exit orifice.    
     
     
         20 . A method in accordance with  claim 19 , further comprising: 
 providing a flow path for said reagent through the injector body, said flow path comprising a fluid inlet arranged in the lower section of said injector body, a hollow portion extending through said metering plug, and a fluid outlet in an upper section of said injector body; and    continuously circulating said reagent through said flow path, thereby enabling continuous cooling of said injector in both the open and closed position of said metering plug.    
     
     
         21 . A method in accordance with  claim 20 , wherein the fluid inlet is proximate the whirl chamber.  
     
     
         22 . A method in accordance with  claim 1 , wherein the whirl slots are arranged transversely to a longitudinal axis of said injector body.  
     
     
         23 . An atomizing injector comprising: 
 a fluid inlet for introducing a reagent into an injector body;    a fluid outlet for removing the reagent from said injector body;    means for providing a predetermined pressure setpoint for pressurizing said reagent in said injector body, said predetermined pressure setpoint being variable within a range of approximately 60 to 80 pounds per square inch;    a whirl chamber for imparting a high velocity rotating flow to at least a portion of said pressurized reagent, said whirl chamber having a plurality of whirl slots; and    a metering plug for metering a precise amount of atomized reagent from an exit orifice into an exhaust gas stream.