Abstract:
An exhaust gas after treatment system for treating exhaust gases from an internal combustion engine is provided. The system includes a soot catalytic converter and an SCR catalytic converter, which reduces NOx-emissions by means of a reagent delivered via an injector located upstream of the SCR catalytic converter. According to the invention the soot catalytic converter is located between the injector and the SCR-catalytic converter.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to an exhaust gas aftertreatment system for treating exhaust gases from an internal combustion engine, comprising a soot catalytic converter and an SCR catalytic converter, which reduces NOx-emissions by means of a reagent delivered via a nozzle located upstream of the SCR catalytic converter. 
         [0002]    Increasing requirements aimed at reducing exhaust emissions from heavy trucks and buses are leading to ever more advanced systems of exhaust gas aftertreatment. SCR (Selective Catalytic Reduction) is one such system for reducing NOx emissions, in which a reagent, in the form a urea/water solution, for example, is injected upstream of an SCR catalytic converter. DPF (Diesel Particulate Filters), in which the soot is burned by means of NO2 (so-called CRT or Continuously Regenerating Trap), is another system which reduces engine particulate emissions (which consist primarily of carbon). NO2 is produced by means of an oxidation catalytic converter located upstream of the particulate filter. 
         [0003]    Various types of particulate filter exist, of which the so-called “wall flow” cordierite filter has been the most commonly used. Another type of filter that has emerged of late is the so-called “flow-through” filter. The latter is characterized in that it has a lower particulate reduction and is ash-permeable, thereby requiring no servicing. 
         [0004]    The more stringent emission requirements are leading to a need to combine these two types of exhaust gas aftertreatment system, which often presents problems of insufficient installation space. 
         [0005]    In hitherto known combined exhaust gas aftertreatment systems (SCR+DPF), the systems comprise components fitted in the following order: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0006]    Variants exist in which a hydrolysis catalytic converter may also be incorporated, primarily into the SCR catalytic converter, and the particulate filter may be catalytically coated, thereby avoiding the first oxidation catalytic converter downstream of the engine. They are all characterized, however, in that the particulate filter is located upstream of the urea injection. This has been essential where “wall flow” cordierite filters were used, due among other things to the fact that these collect ash, primarily calcium sulfate (i.e. gypsum), which presents problems if urea/water solution is injected upstream. They are further characterized by a considerable porous mass, which absorbs the ammonia formed and thereby makes transient urea dosing more difficult. 
         [0007]    It is desirable to provide an effective exhaust gas aftertreatment system which is more compact that known systems. 
         [0008]    The exhaust gas aftertreatment system according to an aspect of the invention for treating exhaust gases from an internal combustion engine comprises a soot catalytic converter and an SCR catalytic converter, which reduces NOx-emissions by means of a reagent delivered via a nozzle located upstream of the SCR catalytic converter and is characterized in that the soot catalytic converter is located between the nozzle and the SCR catalytic converter. This embodiment of the arrangement makes it possible to assemble multiple system components into one compact unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be described in more detail below with reference to exemplary embodiments shown in the drawings attached, in which 
           [0010]      FIG. 1  shows a schematic representation of an internal combustion engine having an exhaust gas aftertreatment system according to the invention, 
           [0011]      FIG. 2  shows in more detail a longitudinal section through a treatment unit forming part of the exhaust gas aftertreatment system according to  FIG. 1 , and 
           [0012]      FIG. 3  correspondingly shows a cross-section through the treatment unit according to  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The internal combustion engine  10  represented schematically in  FIG. 1  comprises an engine block  11  having six piston cylinders  12  with an inlet manifold  13  and an exhaust manifold  14 . Exhaust gases from the engine are led via an exhaust line  15  to a turbine rotor  17  of a turbocharger unit  16 . The turbine shaft  18  drives the compressor wheel  19  of the turbocharger unit, which via an inlet line  20  compresses intake air and delivers it via an intercooler  21  to the inlet manifold  13 . Fuel is fed to each cylinder  12  via injection devices (not shown). Although the figure illustrates a six-cylinder engine, the invention may also be used in conjunction with other cylinder configurations. 
         [0014]    Exhaust gases that have passed through the turbocharger unit  16  are led onwards via the exhaust line  22  to an oxidation catalytic converter  23  for the production of NO2 for the exhaust gas flow. Downstream of the oxidation catalytic converter is a unit  24  for removing soot particles and NOx from the exhaust gas flow, which unit will be described with reference to FIG.  2 . An injector  25  for mixing a reagent, such as urea or ammonia, for example, into the exhaust gas flow, is located upstream of the unit  24 . 
         [0015]    The unit  24  comprises an oval cylindrical casing  26  having two end walls  27 ,  28  and three internal dividing walls  29 ,  30 ,  31 . An inlet pipe  32  extends from the side in through the casing  26  and via a pipe bend onwards in the longitudinal direction of the casing through the three dividing walls  29 - 31  to a distributing space  33  at the end wall  27 . 
         [0016]    Two catalytic converter units  34 ,  35  are fitted in parallel, each in its pipe in the casing, said pipes extending through the three dividing walls  29 - 31  with internal sealing in relation to said walls and external sealing in relation to the outer casing  26 , in order to form two separate internal spaces  36 ,  37  in the casing. The space  36  situated nearest the distributing space  33  communicates via perforations  38  with the exhaust inlet  32 . The space  36  therefore communicates with the distributing space  33  via the inlet pipe  32 . 
         [0017]    A further connection between the distributing space  33  and the space  36  is provided via a pipe  39 , which extends between the distributing space  33  and the space  37 , by the side of the other pipes in the casing  26 . The pipe  39  is provided with perforations into the space  36  on the one hand and into the space  37  on the other. The provision of the pipe  39  allows the otherwise enclosed space  37  to serve as a sound-damping Helmholtz resonator for sound waves that occur in the exhaust gas flow from the engine  10 . In addition, the pipe  39  forms a flow path from the space  36  to the distributing space  33  via said perforations, the flow path reducing the pressure gradient into the distributing space and furthermore increasing the scope for gasifying of the reagent in the exhaust gas flow. 
         [0018]    The distributing space  33  distributes the exhaust gas flow entering via the inlet pipe  32  and the pipe  39  to the two catalytic converter units  34 ,  35 , which are both identically fitted each with its particulate filter  40  of the soot catalytic converter type. The exhaust gas flow from this particulate filter thereafter passes through an SCR-catalytic converter  41 , in which ammonia reacts with NOx to form N2. Finally the exhaust gas flow passes through an oxidation-catalytic converter  42 , which removes any residual ammonia from the exhaust gas flow. The exhaust gas flow is then led via an outlet space  43  to an exhaust outlet  44 . 
         [0019]    The embodiment of the aftertreatment unit  24  according to the invention, in which the exhaust gas flow passes through the particulate filter  40  before it reaches the SCR catalytic converter  41 , allows the injector  25  to be located advantageously close to the unit  24 . Distribution and gasification of the reagent in the exhaust gas flow occurs in the pipes  32 ,  39 , the distributing space  33  and the particulate filter  40 . At the same time it becomes possible to locate the particulate filter, the SCR-catalytic converter and the oxidation catalytic converter as a common unit  24  in one and the same casing  26 . If the injector  25  were instead to be located between the particulate filter and SCR-catalytic converter, the entire exhaust gas aftertreatment system would have to be configured differently, taking up more space. 
         [0020]    The invention must not be regarded as being limited to the exemplary embodiments described above, a number of further variants and modifications being feasible without departing from the scope of the following patent claims. For example, the aftertreatment unit  24  need not be provided with multiple catalytic converter units arranged in parallel.