Abstract:
A burner for an exhaust gas treatment system treats an exhaust flow from an engine and includes an inner housing defining a primary combustion zone and a secondary combustion zone. The inner housing includes a plurality of apertures upstream of the secondary combustion zone for receipt of a first portion of the exhaust flow. An outer housing surrounds the inner housing to define a bypass flow path between the inner and outer housings to bypass a second portion of the exhaust flow around the inner housing outside of the primary and secondary combustion zones. The outer housing includes an exhaust inlet coaxially aligned with an exhaust outlet along a central longitudinal axis. A mixing zone is provided downstream of the second combustion chamber in receipt of the first and second portions of the exhaust flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/437,896, filed on Jan. 31, 2011. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to an exhaust gas treatment device, and more particularly, to a burner within a system for reducing oxides of nitrogen and particulate matter emissions from diesel compression engines. 
     BACKGROUND 
     Governmental bodies continue to call for a reduction in the nitrogen oxides (NO x ) and particulate matter (PM) emitted from diesel combustion processes, and in particular from diesel compression engines. While diesel particulate filters (DPF) are capable of achieving the required reductions in PM, which is typically a form of soot, there is a continuing need for improved systems that can provide the required reductions in NO x , often in connection with the PM reduction provided by a DPF. 
     Systems have been proposed to provide a diesel oxidation catalyst (DOC) upstream from a DPF in order to provide an increased level of NO 2  in the exhaust which reacts with the soot gathered in the DPF to produce a desired regeneration of the DPF. This method may be referred to as passive regeneration. However, such systems may have limited effectiveness at temperatures below 300° C. and typically produce a pressure drop across the oxidation catalyst that must be accounted for in the design of the rest of the system. Additionally, or alternatively, fuel, such as hydrogen or a hydrocarbon fuel, can be delivered upstream of the DOC to generate temperatures greater than 600° F. and actively regenerate the DPF. 
     Some systems include a burner to ignite and combust unburned fuel that remains in the exhaust downstream from the diesel combustion process. Examples of such proposals are shown in commonly assigned and co-pending U.S. patent application Ser. No. 12/430,194, filed Apr. 27, 2009, entitled “Diesel Aftertreatment System” by Adam J. Kotrba et al., the entire disclosure of which is incorporated herein by reference. 
     While current burners for such systems may by suitable for their intended purpose, improvements may be desirable. For example, it may be advantageous to provide a burner having an exhaust gas inlet coaxially aligned with the exhaust gas outlet to reduce back pressure and alleviate component packaging and mounting concerns. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A burner for an exhaust gas treatment system treats an exhaust flow from an engine and includes an inner housing defining a primary combustion zone and a secondary combustion zone. The inner housing includes a plurality of apertures upstream of the secondary combustion zone for receipt of a first portion of the exhaust flow. An outer housing surrounds the inner housing to define a bypass flow path between the inner and outer housings to bypass a second portion of the exhaust flow around the inner housing outside of the primary and secondary combustion zones. The outer housing includes an exhaust inlet coaxially aligned with an exhaust outlet along a central longitudinal axis. A mixing zone is provided downstream of the second combustion chamber in receipt of the first and second portions of the exhaust flow. 
     A burner for an exhaust gas treatment system treats an exhaust flow from an engine and includes a tubular inner housing having a closed upstream end and a central axis. The inner housing defines a combustion flow path to direct a first portion of the exhaust flow through a combustion zone wherein unburned fuel carried in the exhaust is ignited. A tubular outer housing includes an exhaust inlet coaxially aligned with the central axis. The outer housing surrounds the inner housing and defines a bypass flow path across the closed end and between the inner and outer housings to bypass a second portion of the exhaust flow around the combustion zone. An injector tube is fixed to one of the inner housing and the outer housing and is in communication with a cavity of the inner housing. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is schematic depicting an exhaust gas treatment system including a burner constructed in accordance with the teachings of the present disclosure; 
         FIG. 2  is a cross-sectional view of the burner depicted in  FIG. 1 ; 
         FIG. 3  is a perspective view of the burner; 
         FIG. 4  is an end view of the burner; and 
         FIG. 5  is an opposite end view of the burner. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
       FIG. 1  depicts an exemplary diesel exhaust gas aftertreatment system  10  for treating the exhaust from a diesel compression engine  16 . The exhaust may contain oxides of nitrogen (NO x ) such as nitric oxide (NO) and nitrogen dioxide (NO 2 ) among others, particular matter (PM), hydrocarbons, carbon monoxide (CO), and other combustion byproducts. 
     Aftertreatment system  10  includes a burner  18  that selectively increases the temperature of the exhaust by selectively igniting and combusting unburned fuel carried in the exhaust. The ability to provide the exhaust at an elevated temperature to the rest of the system  10  provides a number of advantages, some of which will be discussed in more detail below. 
     Aftertreatment system  10  may also include one or more other exhaust treatment devices, such as a diesel particulate filter (DPF)  20  connected downstream from the burner  18  to receive the exhaust therefrom, and a NO x  reducing device  22 , such as a selective catalytic reduction catalyst (SCR) or a lean NO x  trap connected downstream from the DPF  20  to receive the exhaust therefrom. 
     Burner  18  is operable to increase the temperature of the exhaust of lean-burn engines, such as diesel compression engine  16 , by employing an active regeneration process for the DPF  20  wherein fuel is ignited in the burner  18  to create a flame that heats the exhaust to an elevated temperature that will allow for oxidation of the PM in the DPF  20 . Additionally, in connection with such active regeneration, or independent thereof, burner  18  may be used in a similar manner to heat the exhaust to an elevated temperature that will enhance the conversion efficiency of the NO x  reducing device  22 , particularly an SCR. Advantageously, burner  18  may provide elevated exhaust temperatures, either selectively or continuously, independent of a particular engine operating condition, including operating conditions that produce a low temperature (&lt;300° C.) exhaust as it exits engine  16 . Thus, aftertreatment system  10  can be operated without requiring adjustments to the engine controls. 
     Burner  18  includes an injector  24  for injecting a suitable fuel and an oxygenator. The fuel may include hydrogen or a hydrocarbon. Injector  24  may be structured as a combined injector that injects both the fuel and oxygenator, as shown in  FIG. 2 , or may include separate injectors for the fuel and the oxygenator. Preferably, a control system, shown schematically at  28  in  FIG. 1 , is provided to monitor and control the flows through the injector  24  and the ignition by the igniters  26  using any suitable processor(s), sensors, flow control valves, electric coils, etc. 
     As shown in  FIGS. 2-4 , burner  18  includes a housing  30  constructed as a multi-piece assembly of fabricated sheet metal components. Housing  30  includes a cylindrically-shaped outer housing  32 , a cylindrically-shaped inner housing  34  and a mixer  36  aligned on a central axis  38 . An injector tube  40  extends through an aperture  42  in outer housing  32  as well as an aperture  44  in inner housing  34 . An injector mount  43  is fixed to injector tube  40  to provide an attachment mechanism for injector  24 . Atomized fuel is injected along an injection axis  46 . Injection axis  46  intersects central axis  38  at an included angle “A.” Angle “A” is shown as approximately 52 degrees. Spark plug  26   a  is fixed to outer housing  32  via a mount  48 . An aperture  50  extends through outer housing  32  and another aperture  52  extends through inner housing  34  in receipt of spark plug  26   a . Mount  48  may include portions positioned inside and outside outer housing  32 . Spark plug  26   a  extends along an igniter axis  54  that intersects central axis  38  at an included angle “B.” Angle “B” is also approximately 52 degrees. Spark plug  26   a  includes an end in communication with a first combustion chamber  56  defined by inner housing  34 . Spark plug  26   b  is fixed to outer housing  32  via an igniter mount  55  and extends through apertures  57 ,  59  to be in communication with a second combustion chamber  61  defined by inner housing  34 . 
     Inner housing  34  is depicted as a multi-piece sheet metal subassembly including an inner liner  60 , a transition pipe  62  and an end cap  64  fixed to one another. End cap  64  includes a substantially uninterrupted outer surface  66  with the exception of apertures  44  and  52 . An annular volume  68  exists in the space between outer housing  32  and inner housing  34 . Transition pipe  62  is fixed to end cap  64  and inner liner  60  by a suitable process such as welding. Transition pipe  62  is a substantially contiguous uninterrupted member. Volume  68  is placed in fluid communication with second combustion chamber  61  via a plurality of apertures  72  extending through inner liner  60 . Inner liner  60  also includes an open end  74 . 
     Outer housing  32  is a multi-piece sheet metal fabrication including a cylindrical body  80 , a cylindrical inlet cone  82 , a sleeve  84  and an inlet flange  86  fixed to one another as depicted in the Figures. Inlet cone  82  includes a substantially circular cylindrical portion  92  and a conical portion  94 . Both of these portions have a longitudinal axis coaxially aligned with central axis  38 . Inlet flange  86  and sleeve  84  also include substantially circular cylindrical cross-sections having longitudinal axes aligned with central axis  38 . Inlet flange  86  includes an inlet  96  in receipt of exhaust from engine  16 . Cylindrical body  80  includes an open end  90  having a substantially circular cross-section that is also aligned on central axis  38 . The coaxial arrangement of inlet  96  with open end  74  and open end  90  minimizes the exhaust pressure drop across burner  18 . It should also be appreciated that inner liner  60 , transition pipe  62  and end cap  64  have longitudinal axes that are commonly aligned with central axis  38 . A mounting flange  97  is fixed to outer housing  32  to allow burner  18  to be directly fixed to a downstream exhaust treatment device such as DPF  20 . 
     The shape and positioning of the components of outer housing  32  and inner housing  34  define engine exhaust paths that split and recombine with one another. More particularly, exhaust gas from an internal combustion engine is provided to inlet  96 . Exhaust flows from left to right when viewing  FIG. 2 . As the exhaust continues to flow through inlet flange  86  and sleeve  84 , the exhaust passes through annular volume  68  defined between the outer surfaces of inner housing  34 , such as surface  66 , and an inner surface  91  of outer housing  32 . As the exhaust passes over end cap  64  and transition pipe  62 , a portion of the engine exhaust travels along a combustion flow path  98 . Exhaust travelling along combustion flow path  98  flows through apertures  72 . During burner operation, fuel and oxygenator are supplied to first combustion chamber  56  by injector  24 . Spark plug  26   a  functions as an igniter to produce a flame within first combustion chamber  56 . Exhaust travelling along combustion flow path  98  is heated by the flame and unburned fuel carried in the exhaust is ignited by the flame and/or spark plug  26   b  within second combustion chamber  61 . 
     The remaining portion of exhaust gas that does not pass through apertures  72  may be characterized as travelling along a bypass flow path  100 . Exhaust flows through the volume  68  between inner housing  34  and outer housing  32  downstream of aperture  72 . The exhaust flowing through bypass flow path  100  is supplied to a mixing zone  102  for combination with the combustion flow exiting combustion flow path  98 . 
     Mixer  36  includes an end plate  104  and a mixing plate  106 . End plate  104  extends across the bypass flow path  100  to restrict an available flow area of the bypass flow path  100 . A plurality of elongated apertures  108  extend through mixing plate  106  to define an outlet  110 . Outlet  110  is coaxially arranged with central axis  38 . End plate  104  is fixed to interior surface  91  of the outer housing  32  to secure mixer  36  to burner  18 . Mixer  36  may be constructed from a single, stamped piece of sheet metal. Alternatively, end plate  104  may be constructed separately from and subsequently fixed to mixing plate  106 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.