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The present invention provides methods and apparatus for injecting reagent, 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 d

The present invention provides methods and apparatus for injecting reagent, 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 reagent is passed through the exit orifice into an exhaust stream, atomization occurs from a combination of centrifugal force and shearing of the reagent by air as it jets into the exhaust stream.

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What is claimed is: 1. A low pressure atomizing injector for injecting reagent, comprising: an injector body having an upper section and a lower section; a reagent inlet extending into said lower section of said injector body; a reagent outlet extending out of said upper section of said injector bo

What is claimed is: 1. A low pressure atomizing injector for injecting reagent, comprising: an injector body having an upper section and a lower section; a reagent inlet extending into said lower section of said injector body; a reagent outlet extending out of said upper section of said injector body; a conical whirl chamber having an exit orifice, said whirl chamber arranged on said lower section of said injector body; a plurality of whirl slots in said whirl chamber for imparting a rotational velocity to reagent introduced into said whirl chamber; a valve seat positioned within said whirl chamber surrounding said exit orifice; a metering plug arranged within said injector body, a hollow portion of said metering plug extending within said lower section of said injector body; and an actuator mounted on said injector body and connected to said metering plug for moving said metering plug between closed and open positions; wherein: said reagent inlet and reagent outlet communicate with said whirl chamber via a hollow portion of said metering plug; and said reagent inlet, said whirl slots, said whirl chamber, said hollow portion of said metering plug, and said reagent outlet provide a flow path for reagent through said injector body, thereby enabling continuous cooling of said injector in both the open and closed position of said metering plug. 2. An injector according to claim 1, wherein: in said open position, atomized reagent is dispensed from said exit orifice at a rate of approximately 3 to 500 grams per minute. 3. An injector according to claim 1, further comprising a metering orifice in the reagent outlet for controlling the amount of said cooling reagent flowing through said flow path. 4. An injector according to claim 1, wherein: said hollow portion of said metering plug extends substantially through a length of said metering plug. 5. An injector according to claim 4 wherein: a plurality of bores are provided in a tip section of said metering plug proximate the whirl chamber, said plurality of bores being connected with a first end of said hollow portion of said metering plug; an outlet section is provided in a top portion of said metering plug opposite said tip section, said outlet section being connected with a second end of said hollow portion of said metering plug; and reagent flows from said reagent inlet, into said plurality of bores, through said hollow portion, out of said outlet section of said metering plug, and into said reagent outlet independent of the position of said metering plug. 6. An injector according to claim 1, further comprising a plurality of ribs surrounding said injector body for dispersing heat away from said injector body. 7. An injector according to claim 1, further comprising a heat shield surrounding said exit orifice, said heat shield having an aperture therethrough aligned with said exit orifice, thereby allowing reagent released from said whirl chamber to pass through said heat shield. 8. An injector according to claim 7, wherein said heat shield comprises: a plate surrounding said exit orifice; and a layer of insulating material arranged on said plate. 9. An injector according to claim 1, wherein said injector body and said metering plug comprise stainless steel. 10. An injector according to claim 1, further comprising a biasing member located within said injector body for biasing said metering plug into said closed position. 11. An injector according to claim 10, wherein said biasing member comprises a coil spring coaxially arranged with said metering plug. 12. An injector according to claim 10, wherein said actuator comprises: a magnetic coil generating a magnetic force, said magnetic force effecting a sliding motion of said metering plug against said biasing member when said magnetic coil is energized thereby moving said metering plug from said closed position to said open position within said whirl chamber to enable reagent to be released from said whirl chamber through said exit orifice; and means for energizing said magnetic coil. 13. An injector according to claim 1, wherein said reagent comprises a urea solution. 14. An injector according to claim 1, wherein said reagent comprises a hydrocarbon. 15. An injector in accordance with claim 1, further comprising: means for introducing the reagent into the injector body; means for providing a predetermined pressure setpoint for pressurizing said reagent in said injector body; wherein said metering plug meters a precise amount of said reagent having said rotational velocity from said exit orifice. 16. An injector according to claim 15, wherein the reagent comprises a urea solution. 17. An injector according to claim 15, wherein said reagent comprises a hydrocarbon. 18. An injector according to claim 15, wherein said gas stream comprises a diesel exhaust stream. 19. An injector according to claim 15, wherein said predetermined pressure setpoint varies in response to operating conditions to provide at least one of increased operating range and varied spray patterns. 20. An injector in accordance with claim 15, wherein varying said predetermined pressure setpoint varies a droplet size of said reagent metered from said exit orifice. 21. An injector in accordance with claim 20, wherein said droplet size is within a range of approximately 50 μm SMD or smaller. 22. An injector in accordance with claim 15, wherein varying said predetermined pressure setpoint varies a flow rate of said reagent metered from the exit orifice. 23. An injector in accordance with claim 22, wherein said flow rate of said reagent metered from said exit orifice is in a range of approximately 3 to 500 grams per minute. 24. An injector in accordance with claim 22, wherein varying the flow rate further varies at least one of (1) a droplet size of said reagent metered from said exit orifice; and (2) an amount of cooling provided by circulating reagent remaining in the injector body through the injector body. 25. An injector according to claim 1, wherein said reagent is circulated through said flow path to maintain said reagent in said injector body within a desired temperature range. 26. An injector according to claim 25, wherein said desired temperature range comprises 5�� C. to 85�� C. 27. An injector in accordance with claim 1, wherein a pressure of said reagent in said injector body is in a range of approximately 60 to 80 pounds per square inch. 28. An injector in accordance with claim 1, wherein said plurality of whirl slots comprises at least four whirl slots. 29. An injector 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. 30. An injector in accordance with claim 29, wherein different whirl plates with correspondingly different characteristics can be interchanged in said injector body for different applications of said injector. 31. An injector in accordance with claim 30, wherein said different whirl plates provide different spray patterns of said reagent metered from said exit orifice. 32. An injector in accordance with claim 30, 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. 33. An injector in accordance with claim 1, wherein the whirl slots are arranged transversely to a longitudinal axis of the metering plug. 34. An injector in accordance with claim 1, wherein the reagent inlet is proximate the whirl chamber. 35. An injector in accordance with claim 1, wherein: all reagent flowing through said injector body flows through said plurality of whirl slots and into said whirl chamber to provide maximum cooling of said whirl chamber and maximum rotational velocity to said reagent in said whirl chamber. 36. An injector in accordance with claim 1, wherein: said exit orifice is recessed from a tip of the injector to limit exposure of said exit orifice to high temperatures and to minimize fouling and deposits proximate said exit orifice. 37. An injector in accordance with claim 1, wherein: an amount of reagent circulated through said injector body for said cooling is greater than an amount of reagent dispensed from said exit orifice. 38. A method for injecting atomized reagent at low pressure, comprising: introducing a reagent into a lower section of an injector body; imparting a rotational velocity to said reagent by circulating said reagent through a conical whirl chamber having a plurality of whirl slots, said whirl chamber arranged on said lower section of said injector body; controlling movement of a metering plug arranged within the injector body between closed and open positions; providing a flow path through the injector body, said flow path comprising a reagent inlet arranged in said lower section of said injector body, said whirl slots, said whirl chamber, a hollow portion extending through said metering plug, and a reagent outlet arranged in an upper section of said injector body; 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; metering atomized reagent from an exit orifice of the whirl chamber when said metering plug is in said open position. 39. A method in accordance with claim 38, wherein: an amount of reagent circulated through said injector body for said cooling is greater than an amount of reagent metered from said exit orifice.