Abstract:
A system for controlling the temperature of an exhaust stream includes a main exhaust passageway adapted to receive the exhaust stream from an engine. A bypass passage includes an inlet and an outlet in communication with the main exhaust passageway. The outlet is located downstream from the inlet. A burner is positioned within the bypass passage for treating the exhaust passing through the bypass passage. A valve is positioned within the main exhaust passageway downstream from the inlet and upstream from the outlet. The valve is operable to vary the exhaust flow through the burner. A controller selectively operates the burner to maintain a desired exhaust temperature downstream of the outlet.

Description:
FIELD 
       [0001]    The present disclosure generally relates to a system for treating exhaust gases. More particularly, a flow diverter and burner arrangement for increasing an exhaust gas temperature is discussed. 
       BACKGROUND 
       [0002]    In an attempt to reduce the quantity of NO X  and particulate matter emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment devices have been developed. A need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented. Typical aftertreatment systems for diesel engine exhaust may include one or more of a diesel particulate filter (DPF), a selective catalytic reduction (SCR) system, a hydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC). 
         [0003]    During engine operation, the DPF traps soot emitted by the engine and reduces the emission of particulate matter (PM). Over time, the DPF becomes loaded and begins to clog. Periodically generation or oxidation of the trapped soot in the DPF is required for proper operation. To regenerate the DPF, relatively high exhaust temperatures in combination with an ample amount of oxygen in the exhaust stream are needed to oxidize the soot trapped in the filter. 
         [0004]    The DOC is typically used to generate heat to regenerate the soot loaded DPF. When hydrocarbons (HC) are sprayed over the DOC at or above a specific light-off temperature, the HC will oxidize. This reaction is highly exothermic and the exhaust gases are heated during light-off. The heated exhaust gases are used to regenerate the DPF. 
         [0005]    Under many engine operating conditions, however, the exhaust gas is not hot enough to achieve a DOC light-off temperature of approximately 300° C. As such, DPF regeneration does not passively occur. Furthermore, NO X  adsorbers and selective catalytic reduction systems typically require a minimum exhaust temperature to properly operate. 
         [0006]    A burner may be provided to heat the exhaust stream upstream of the various aftertreatment devices. Known burners have successfully increased the exhaust temperature of relatively small displacement internal combustion engines for automotive use. However, other applications including diesel locomotives, stationary power plants, marine vessels and others may be equipped with relatively large diesel compression engines. The exhaust mass flow rate from the larger engines may be more than ten times the maximum flow rate typically provided to the burner. While it may be possible to increase the size of the burner to account for the increased exhaust mass flow rate, the cost, weight and packaging concerns associated with this solution may be unacceptable. Therefore, a need may exist in the art for an arrangement to increase the temperature of the exhaust output from a large diesel engine while minimally affecting the cost, weight, size and performance of the exhaust system. It may also be desirable to minimally affect the pressure drop and/or back pressure associated with the use of a burner. 
       SUMMARY 
       [0007]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0008]    A system for controlling the temperature of an exhaust stream includes a main exhaust passageway adapted to receive the exhaust stream from an engine. A bypass passage includes an inlet and an outlet in communication with the main exhaust passageway. The outlet is located downstream from the inlet. A burner is positioned within the bypass passage for treating the exhaust passing through the bypass passage. A valve is positioned within the main exhaust passageway downstream from the inlet and upstream from the outlet. The valve is operable to vary the exhaust flow through the burner. A controller selectively operates the burner to maintain a desired exhaust temperature downstream of the outlet. 
         [0009]    A system for controlling the temperature of an exhaust from an engine includes a bypass passage having an inlet in communication with a main exhaust passageway in receipt of an exhaust stream from the engine. The bypass passage also includes an outlet in communication with the main exhaust passageway at a location downstream from the inlet. A burner is positioned within the bypass passage for heating the exhaust passing through the bypass passage. A valve is positioned within the main exhaust passageway downstream from the inlet and upstream from the outlet. The valve is operable to vary the exhaust flow through the burner. An exhaust aftertreatment device is located downstream of the outlet in receipt of a mixed exhaust supplied from the bypass passage and the main exhaust passageway. 
         [0010]    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 
         [0011]    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. 
           [0012]      FIG. 1  is a schematic depicting a system for controlling the temperature of an exhaust from an engine; 
           [0013]      FIG. 2  is a side view of a valve from the temperature control system in a closed position; 
           [0014]      FIG. 3  is an end view of the valve of  FIG. 2  in the closed position; 
           [0015]      FIG. 4  is side view of the valve of  FIG. 2  in a fully open position; and 
           [0016]      FIG. 5  is an end view of the valve of  FIG. 2  shown in a fully open position. 
       
    
    
       [0017]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0018]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0019]      FIG. 1  depicts a diesel exhaust gas aftertreatment system  10  for treating the exhaust output by engine  12  to a main exhaust passageway  14 . An intake passage  16  is coupled to engine  12  to provide combustion air thereto. A turbocharger  18  includes a driven member  20  positioned in an exhaust stream flowing through main exhaust passageway  14  as well as a drive member  22  positioned within intake passage  16  and in communication with intake air. During engine operation, the exhaust stream causes driven member  20  to rotate. Because drive member  22  is fixed for rotation with driven member  20 , intake air is compressed within intake passage  16  prior to entry into engine  12 . 
         [0020]    Exhaust aftertreatment system  10  also includes a valve and burner arrangement  26  positioned downstream from turbocharger  18  and upstream from a number of exhaust aftertreatment devices. In the exemplary aftertreatment system depicted in  FIG. 1 , the aftertreatment devices include a hydrocarbon injector  28 , a diesel oxidation catalyst  30 , a diesel particulate filter  32 , a urea injector  34  and a selective catalytic reduction system  36 . 
         [0021]    It is contemplated that engine  12  is configured as a relatively large displacement diesel compression engine having an exhaust mass flow rate ranging from 3000 to 20,000 kg per hour depending on engine operating speed. It should be appreciated that this mass flow rate range is merely exemplary and that the teachings of the present disclosure may be applied to other engines having different exhaust mass flow rates. It is further contemplated that engine  12  typically operates as a lean-burn engine having exhaust temperatures oftentimes less than 300° C. As previously mentioned, proper operation of many of the exhaust aftertreatment devices occurs when the exhaust gas temperature entering the aftertreatment device exceeds 300° C. Accordingly, burner and valve arrangement  26  is provided upstream of the exhaust aftertreatment devices. 
         [0022]    Burner and valve arrangement  26  includes a burner  40  and a valve  42  positioned within parallel portions of system  10 . In particular, burner  40  is positioned within a bypass passage  44  having an inlet  46  positioned upstream of valve  42  and in communication with main exhaust passageway  14 . A bypass outlet  48  is positioned downstream of valve  42  and in communication with main exhaust passageway  14 . Bypass outlet  48  is upstream from each of exhaust aftertreatment devices  28 ,  30 ,  32 ,  34  and  36 . As such, burner  40  may be used to heat the exhaust to an elevated temperature that will enhance the efficiency of DOC  30  and SCR system  36 . 
         [0023]    Burner  40  may include one or more injectors  52  for injecting fuel as well as one or more oxygenators  54 . One or more igniters  55  function to ignite the injected fuel and oxygen together with unburned fuel already carried in the exhaust. Alternatively, each injector  52  may be a combined injector that injects both fuel and oxygen. A controller  56  is provided to monitor and control the flow of the fuel and/or oxygen through injectors  52 ,  54  as well as the operation of igniters  55 . 
         [0024]    Valve  42  is a passive snap-action valve positioned within a tubular portion  60  of main exhaust passageway  14  downstream of bypass inlet  46  and upstream of bypass outlet  48 . Valve  42  is depicted in  FIGS. 2 and 3  to include a spring anchor  64 , a valve spring  66 , an external lever arm  68 , a valve flap  70 , a valve support shaft or axle  72  and an attachment point  74  protruding from axle  72 . 
         [0025]    Valve flap  70  has first and second arcuate edges substantially conforming to an interior arcuate surface of tube  60 . Flap  70  additionally has linear side edges  76  and  78  which provide clearance  80 ,  82  between flap  70  and an interior surface of tube  60  when the flap is in the closed position shown in  FIGS. 2 and 3 . Bias element or spring  66  extends between a spring anchor  64  on tube  60  and attachment point  74  of external lever arm  68 . Spring  66  biases flap  70  toward the closed positioned shown in  FIG. 2 . When in the fully closed position, flap  70  resides at an angle other than 90° to a plane extending normal to the longitudinal axis of tube  60 . The angle of the flap with respect to a cross-sectional normal plane of tube  60  is designated A. 
         [0026]    In operation, exhaust pressure acts on flap  70  from the left as viewed in  FIGS. 2-5 . When the exhaust pressure is sufficient to overcome the bias force of spring  66 , the flap  70  will start to rotate about axle  72 . The torque on valve flap  70  is determined by the bias spring force multiplied by a distance d. Distance d is the distance between the axis of spring  66  and axle  72 . The spring force increases as the valve flap opens and spring  66  stretches. However, d gets shorter as the valve continues to open resulting in the torque approaching zero as the longitudinal axis of the spring approaches an “over-center” position. Distance d reduces as the spring axis approaches intersection with a longitudinal axis of axle  72 . This nearly over-center positioning of the valve flap  70  as shown in  FIGS. 4 and 5  results in a substantially horizontal position of the flap when in the fully open position. This positioning, in turn, minimizes back pressure in the tube when the valve is in the fully open position. Additionally, it is to be noted that the tube itself supplies the stop mechanism for the valve flap in both its fully closed and fully opened positions. In the fully closed position, the arcuate edges of flap  70  contact the interior surface of tube  60  to define that position. Conversely, when in the fully opened position, as shown in  FIGS. 4 and 5 , flap  70  utilizes its lateral linear side edges ( 76  and  78  of  FIG. 3 ) to come into contact with the inner surface of tube  60  to thereby provide a stop position for the fully opened position of flap  70 . 
         [0027]    Rotating the valve flap such that the spring approaches the over-center condition also results in an easier maintenance of the valve in the fully opened position. It should be appreciated that the configuration of valve flap  70  is merely exemplary and that other snap-action valves are contemplated for use within burner and valve arrangement  26 . Specifically, U.S. Pat. No. 7,434,570 and U.S. Patent Application Publication Nos. 2008-0223025 and 2008- 0245063  are herein incorporated by reference and depict alternate suitable valves. 
         [0028]    Controller  56  is also in receipt of signals from various sensors  84  associated with aftertreatment system  10  and engine  12 . For example, sensors  84  may include individual sensors for collecting specific data or may broadly refer to data available over a CAN bus. When engine  12  and aftertreatment system  10  are used in a vehicle, the information provided to controller  56  may include battery voltage and ignition switch position data. Additional sensors including a mass air flow sensor, air flow and fuel flow sensors associated with injector  52 , a fuel pressure sensor, an air pressure sensor, a burner inlet temperature sensor, a burner outlet temperature sensor and/or an exhaust gas temperature sensor downstream of bypass outlet  48  may also be associated with aftertreatment system  10  and in communication with controller  56 . 
         [0029]    It should be appreciated that exhaust aftertreatment system  10  may be operated in a number of different modes. In a first mode of operation, controller  56  may be in receipt of a command to operate burner  40  in an active mode. This mode of operation may be entered when the vehicle ignition is on and other sensor data indicates that engine  12  is combusting fuel. During operation of engine  12 , controller  56  commands burner  40  to maintain a desired exhaust gas temperature. The control temperature data may be provided by a sensor  86  ( FIG. 1 ) at the burner outlet. Alternatively or additionally, an exhaust gas temperature sensor  88  may be positioned further downstream from the interconnection of bypass outlet  48  and main exhaust passageway  14  to determine the temperature of the mixed exhaust gas entering DOC  30 . Controller  56  may operate burner  40  to maintain a desired mixed exhaust temperature as indicated by sensor  88 . Burner control continues until controller  56  indicates that engine  12  has ceased operation and/or the ignition switch is in the off position. 
         [0030]    It should be noted that valve  42  is passively operated and that the position of flap  70  varies based on exhaust fluid pressure applied to flap  70 . The angle of flap  70  at the closed position, the initial preload and rate of spring  66 , as well as the position of axle  72  will be determined and defined to assure that the proper flow of exhaust is diverted into bypass passage  44  and burner  40 . Controller  56  may selectively actuate injectors  52 ,  54  and igniters  55  to heat the exhaust gas flowing through bypass outlet  48  to maintain a target temperature. 
         [0031]    In another mode of operation, burner  40  may be used to perform active regeneration of DPF  32  after engine  12  has been shut off. In certain operating conditions, engine  12  will cool more rapidly than desired if continued passive regeneration of DPF  32  is desired. Accordingly, controller  56  may activate burner  40  to heat the exhaust gas within main exhaust passageway  14  to regenerate DPF  32  after engine  12  has been shut off. The burner  40  heats the exhaust gas when the exhaust flow has effectively been stopped. 
         [0032]    Another mode of operating exhaust aftertreatment system  10  includes monitoring the use of fresh air inputs to engine  12  or exhaust aftertreatment system  10  that are not heated by the combustion process of engine  12 . Such systems may include a dynamic brake where relatively cold ambient air may be pumped through engine  12  when combustion does not occur in an attempt to retard the vehicle. The cool air is then provided to DOC  30 , DPF  32  and/or SCR system  36 . Some of the components within the exhaust aftertreatment devices  30 ,  32  and  36  may be adversely affected when exposed to a thermal shock such as during dynamic engine braking. Accordingly, it may be desirable to operate burner  40  during engine braking to assure that the exhaust gas entering the aftertreatment devices will be at or above a minimum temperature. 
         [0033]    During times when engine  12  operates at a relatively high load and/or operating speed, it is contemplated that valve  42  will be in a substantially open condition and that the temperature of the exhaust within main exhaust passageway  14  will exceed a predetermined minimum temperature for proper operation of exhaust aftertreatment devices  30 ,  32  and  36 . Accordingly, controller  56  will maintain burner  40  at an idle state where fuel is not injected through injector  52  and igniters  55  are not energized. When engine  12  operates at lower loads and lower operating speeds, the exhaust gas temperature will likely decrease. Once controller  56  determines that the exhaust gas temperature upstream from DOC  30  is at or below a predetermined threshold, burner  40  will be operated in its active mode to maintain either a desired burner outlet temperature or a mixed gas temperature upstream from the exhaust aftertreatment devices. 
         [0034]    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.