Abstract:
An ammonia (reductant) injector for delivering a ammonia into an engine exhaust stream is disclosed. Generally speaking, the injector has a body with an inlet fluidly coupled to a plurality of channels within the body, a plurality of discharge ports, each port being fluidly coupled to at least one channel, and an ammonia feed line connected to the inlet of the body. The plurality of discharge ports are preferably spaced one from another such as to optimize the dispersion of ammonia from the ports throughout a cross-sectional portion of an engine exhaust stream.

Description:
TECHNICAL FIELD 
       [0001]    The present device relates to a gas injector for a vehicle exhaust after-treatment system. Specifically, the device relates to an ammonia gas injector for NOx reduction in a vehicle exhaust after-treatment system. 
       BACKGROUND 
       [0002]    Compression ignition engines provide advantages in fuel economy, but produce both NO x  and particulates during normal operation. New and existing regulations continually challenge manufacturers to achieve good fuel economy and reduce the particulates and NO x  emissions. Lean-burn engines achieve the fuel economy objective, but the high concentrations of oxygen in the exhaust of these engines yields significantly high concentrations of NO x  as well. Accordingly, the use of NO x  reducing exhaust treatment schemes is being employed in a growing number of systems. 
         [0003]    One such system is the direct addition of a reductant or reducing agent, such as ammonia gas, to the exhaust stream. It is an advantage to deliver ammonia directly into the exhaust stream in the form of a gas, both for simplicity of the flow control system and for efficient mixing of the reducing agent, ammonia, with the exhaust gases. The direct use of ammonia also eliminates potential difficulties related to blocking of the dosing system, which may be caused by precipitation or impurities, e.g., in a liquid-based urea solution. In addition, an aqueous urea solution cannot be dosed at a low engine load since the temperature of the exhaust line would be too low for complete conversion of urea to ammonia (and CO 2 ). 
         [0004]    A couple specific challenges with the direct injection of ammonia relate to dispersion and mixing of the reducing agent with the hot exhaust gases. The dispersion issue considers how to deliver or spread ammonia to the greatest volume of flowing exhaust, while the mixing issue questions how to create the most homogenous mixture of exhaust and ammonia to facilitate NOx reduction. 
         [0005]    Thus, the present system provides both a device for adequately dispersing and sufficiently mixing a reductant, such as ammonia into an exhaust gas stream of a vehicle. These and other problems are addressed and resolved by the disclosed system and method of the present application. 
       SUMMARY 
       [0006]    There is disclosed herein a device which avoids the disadvantages of prior devices while affording additional structural and operating advantages. 
         [0007]    Generally, a reductant injector for delivering reductant into an engine exhaust stream comprises a body having an inlet fluidly coupled to a plurality of channels within the body, a plurality of discharge ports, each port being fluidly coupled to at least one channel, and a reductant feed line connected to the inlet of the body. The plurality of discharge ports are preferably spaced one from another such as to optimize the dispersion of reductant from the ports throughout a cross-sectional portion of an engine exhaust stream. 
         [0008]    In an embodiment, an aspect of the subject injector includes discharging the reductant from the ports in a direction perpendicular the engine exhaust stream travel. In another embodiment, the injector ports discharge reductant in a direction parallel to the engine exhaust stream, preferably in an upstream direction. An aspect of the latter configuration includes shielding of the ports to prevent plugging. 
         [0009]    In an embodiment, the injector comprises four discharge ports. Preferably, the four ports are spaced approximately 90 degrees from one another. An aspect of this configuration includes the body being shaped like a cross having four arms at the end of each of which is positioned a discharge port. 
         [0010]    In an embodiment, the reductant feed line positions the injector within an engine exhaust stream, most preferably proximate the center of the stream. It is an aspect of this embodiment that the feed line provides stability to the injector. 
         [0011]    In an embodiment, the reductant may be ammonia. 
         [0012]    These and other aspects of embodiments of the invention are described in the following detailed description and shown in the appended drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. The components in the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the following description and throughout the numerous drawings, like reference numbers are used to designate corresponding parts. 
           [0014]      FIG. 1  is a side cross-sectional view of a vehicle after-treatment system illustrating an embodiment of the present NOx reduction system positioned within the vehicle exhaust gas; 
           [0015]      FIG. 2  is a side cross-sectional view of the vehicle after-treatment system similar to that shown in  FIG. 1 , further illustrating exhaust gas flow, ammonia gas dispersion and mixing of the two; 
           [0016]      FIG. 3  is a close-up of the upstream side of an embodiment of the NOx reduction system; 
           [0017]      FIG. 4  is a close-up of an embodiment of the injector; 
           [0018]      FIG. 5  is a perspective view of an embodiment of the ammonia injector; 
           [0019]      FIGS. 6A-B  are side views of an alternate embodiment of the ammonia injector; 
           [0020]      FIG. 7  is a perspective view of an embodiment of the ammonia injector positioned upstream of an embodiment of the mixing plate; 
           [0021]      FIG. 8  is a side view of an embodiment of the mixing plate; 
           [0022]      FIG. 9  is a front perspective of the mixing plate shown in  FIG. 9 ; and 
           [0023]      FIG. 10  is a side view illustrating the use of the mixing plate to support the injector. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    With reference to  FIGS. 1-10 , embodiments of a system and methods are described to one of skill in the relevant art. Generally speaking, a NOx reduction system, designated with the reference number  10  in the figures, typically works in conjunction with an exhaust gas after-treatment system  12  and comprises a mixing chamber  22 , an ammonia injector  20  and a mixing plate  50 . Typically, the reductant provided for use in the system  10  is carried on-board in canisters (not shown) which require periodic recharging. While embodiments using ammonia as the preferred reductant are disclosed, the invention is not limited to such embodiments, and other reductants may be utilized instead of, or in addition to, ammonia for carrying out the inventions disclosed and claimed herein. Examples of such other, or additional reductants include, but are not limited to, urea, ammonium carbamate, and hydrogen. 
         [0025]      FIGS. 1 and 2  illustrate a vehicle exhaust after-treatment system  12  having, in downstream direction, an exhaust inlet  16 , a diesel oxidation catalyst (DOC) canister  17 , the NOx reduction device  10 , a NOx particulate filter (NPF) canister  18 , and an outlet  19 .  FIG. 2  further illustrates the exhaust stream flow before the NOx reduction device  10  (flow A), during mixing (flow B) and after the device  10  (flow C). Flow A is comprised entirely of engine exhaust gases, while the composition of flow B is (1) exhaust gases, (2) ammonia gas, and (3) a mixed gas, and flow C is comprised almost entirely of mixed gas. 
         [0026]      FIG. 3  shows the preferred centered positioning of the injector  20  within the mixing chamber  22  (i.e., the space between the DOC and the NPF). Positioning the injector  20  in the chamber  22  center allows for optimum dispersion of the ammonia gas from a fixed, single, multi-port injector  20 . 
         [0027]    Referring to  FIGS. 3-6 , preferred embodiments of the injector  20  are illustrated. Generally, the injector  20  comprises an inlet  24  which couples directly to an ammonia feed line  26  at one end and to the injector body  28  at the other end. The inlet  24  is preferably on a back surface of the injector body  28 , as illustrated in  FIGS. 1 and 2 . Alternatively, the inlet  24  may be positioned between two adjacent arms  30 , as shown in  FIG. 4 . Multiple discharge ports  32  are used to disperse ammonia throughout the mixing chamber  22 . In the embodiment of  FIGS. 3-6 , four discharge ports  32 A-D are positioned one at the end of each of four arms  30 A-D. As shown in  FIGS. 3-5 , the injector  20  is formed in the shape of a cross, separating the ports  32 A-D by about 90 degrees one from another. A plurality of channels  34  within the injector  20  direct the ammonia gas from the inlet  24  to the discharge ports  32 . 
         [0028]    While other multi-port injector configurations are possible, the four-port cross-injector  20  shown has proven to be most effective at disbursing ammonia throughout the mixing chamber  22 . The injector  20  is positioned substantially in the center of the mixing chamber  22  with the discharge ports  32  aimed in a direction perpendicular (or substantially perpendicular) to the exhaust stream flow. 
         [0029]    In an alternate embodiments shown in  FIGS. 6A-B , the injector discharge ports  32  are aimed directly upstream ( FIG. 6A ) or at some angle greater than zero incident to the exhaust stream ( FIG. 6B ) to disburse ammonia. However, such a configuration exposes the ports to plugging. Accordingly, to prevent plugging of the discharge ports  32  with exhaust particulates, shrouds  40  are used to shield each of the ports  32 . The shrouds  40  are attached to the body  28  of the injector  20  and are preferably conical in shape to minimize the creation of exhaust backflow. The number of shrouds  40  should correspond to the number of ports  32 , but it may be conceivable to cover more than a single port with a shroud for some applications. 
         [0030]    Another important aspect of the NOx reduction system  10 , is the use of mixing plate  50 . Referring to  FIGS. 7-9 , the mixing plate  50  is comprised of a multi-faced, multi-armed body  52 , with at least two tiers of cutouts  54  dispersed about the circumference of the plate  50 . The mixing plate  50  is positioned downstream of the injector  20 , as shown in  FIG. 1 . 
         [0031]    In the illustrated embodiment, the mixing plate body  52  has four arms  56  extending from the plate center  57 . Each arm  56  has a surface or face  58  and is similarly angled or twisted to one side, much like a fan blade, as best shown in  FIG. 8 . The angled plate face  58  is used to deflect the gas streams, as shown in  FIG. 3 , and create turbulent flow to cause efficient mixing. Tabs  59  at the end of each arm  56 , with reference to  FIG. 9 , provide a surface for attachment of the mixing plate  50  to the canister wall  62 . Other attachment means may be equally suitable. 
         [0032]    The cutouts  54  are considered to be two-tiered because of the distance each is from the plate center. The first tier cutouts  54 A are positioned between adjacent arms  56  and extend closest to the plate center, while the second tier cutouts  54 B are centered at the top of each arm  56  and are shorter. As a result, the mixing gases—i.e., exhaust gases and ammonia gas—are diverted laterally before passing the plate  50  into the NPF  18 . Additional cutout tiers may be used if desired. Further, while the preferred cutouts  54  are shown to be semi-circular, other shapes and sizes may be used to accomplish the desired distribution of gases within the mixing chamber  22 . 
         [0033]    Another function of the mixing plate  50  is as a support for the injector  20 . As shown in  FIG. 10 , the ammonia feed line  26  may come into the mixing chamber  22  from downstream of the mixing plate  50  and then passes through the plate to position the injector  20  at the chamber center. The plate  50 , which is secured at several points to the canister wall  62 , stabilizes the injector  20 , via the ammonia feed line, which is otherwise secured at a single point. 
         [0034]    It should be emphasized that the above-described embodiments of the present invention, particularly, any “preferred” embodiments, are possible examples of implementations merely set forth for a clear understanding of the principles for the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without substantially departing from the spirit and principles of the invention. All such modifications are intended to be included herein within the scope of this disclosure and the present invention, and protected by the following claims.