Patent Abstract:
A cold start NO 2  generation system includes a catalyst control module that identifies a portion of a three-way catalyst that corresponds to a nitrogen dioxide zone. A diagnostic module determines a temperature in the nitrogen dioxide zone, and a fuel control module adjusts an air/fuel ratio based on the temperature in the nitrogen dioxide zone. 
     A cold start NO 2  generation method includes identifying a portion of a three-way catalyst that corresponds to a nitrogen dioxide zone. The method further includes determining a temperature in the nitrogen dioxide zone and adjusting an air/fuel ratio based on the temperature in the nitrogen dioxide zone.

Full Description:
FIELD 
       [0001]    The present disclosure relates to cold start emission strategies, and more particularly to maximization of NO 2  generation during a cold start of an engine. 
       BACKGROUND 
       [0002]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0003]    Combustion in an engine results from ignition of a compressed air/fuel mixture in a cylinder of the engine. The exhaust gas resulting from combustion of the air/fuel mixture is expelled to an exhaust system. One or more engine parameters affecting the quantities of air and fuel in the air/fuel mixture may be adjusted by a controller based on signals from various sensors that are located in the exhaust system. The temperature of the engine will also affect the quantities of air and fuel in the air/fuel mixture. For example, during a cold start of the engine, the air/fuel mixture may be more heavily concentrated with fuel and then becomes less concentrated as the temperature of the engine increases. 
       SUMMARY 
       [0004]    A cold start NO 2  generation system includes a catalyst control module that identifies a portion of a three-way catalyst that corresponds to a nitrogen dioxide zone. A diagnostic module determines a temperature in the nitrogen dioxide zone, and a fuel control module adjusts an air/fuel ratio based on the temperature in the nitrogen dioxide zone. 
         [0005]    A cold start NO 2  generation method includes identifying a portion of a three-way catalyst that corresponds to a nitrogen dioxide zone. The method further includes determining a temperature in the nitrogen dioxide zone and adjusting an air/fuel ratio based on the temperature in the nitrogen dioxide zone. 
         [0006]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0008]      FIG. 1  is a schematic illustration of an exhaust assembly according to the present disclosure; 
           [0009]      FIG. 2  is a schematic illustration of a control module of the exhaust assembly according to the present disclosure; and 
           [0010]      FIG. 3  is an illustration of a flow diagram for operation of a cold start NO 2  generation method according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The following description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0012]    As used herein, the term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor. 
         [0013]    The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors or a group of execution engines. For example, multiple cores and/or multiple threads of a processor may be considered to be execution engines. In various implementations, execution engines may be grouped across a processor, across multiple processors, and across processors in multiple locations, such as multiple servers in a parallel processing arrangement. In addition, some or all code from a single module may be stored using a group of memories. 
         [0014]    The apparatuses and methods described herein may be implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage. 
         [0015]    The fuel efficiency of an engine increases if the engine is allowed to run in a lean operation mode (for example, where there is more oxygen and less fuel). While operating in a stoichiometric mode (for example, where there is equimolar fuel and oxygen), particularly during engine cold starts, a three-way catalyst operates to reduce nitric oxide (NO) in emissions. Lean operation may be delayed (for example, by at least 200 seconds) until the temperature of a selective catalytic reduction (SCR) system reaches a temperature threshold where the SCR system can be activated for reducing NO under the lean operation. 
         [0016]    A cold start NO 2  generation system according to the present disclosure reduces the delay by providing an NO 2  generation zone within the three-way catalyst to convert nitric oxide (NO) to nitrogen dioxide (NO 2 ) and store the NO 2  in the SCR system. Accordingly, the NO 2  generation zone is separated from a hydrocarbon (HC) oxidation zone that functions to oxidize hydrocarbons. The HC oxidation zone and NO 2  generation zone are separated because the presence of HC prohibits NO 2  generation. NO 2  generation is delayed until all HC is oxidized, and lean operation cannot occur until enough NO 2  forms to be stored in the SCR system. 
         [0017]    The NO 2  is oxidized to generate ammonium nitrate (ammonia, NH 4 NO 3 ) according to: 
         [0000]    
       
         
           
             
               
                 NO 
                 2 
               
               + 
               
                 NO 
                 2 
               
             
              
             
               ↔ 
               
                 + 
                 
                   O 
                   
                     2 
                     - 
                   
                 
               
             
              
             
               
                 NO 
                 3 
                 - 
               
               + 
               
                 NH 
                 4 
                 + 
               
             
             ↔ 
             
               
                 NH 
                 4 
               
                
               
                 NO 
                 3 
               
             
           
         
       
     
         [0000]    The ammonium nitrate is stored in the SCR system. The SCR system uses the ammonium nitrate to react with the NO in the emissions gas that flows through the exhaust system during lean operation of the engine. When the SCR system becomes thermally activated, the SCR system will reduce the ammonium nitrates using ammonia (NH 3 ) separately generated from the three way catalyst. The NO 2  generation zone of the three-way catalyst (and the three-way catalyst as a whole) is not required to generate NO 2  after the SCR system is thermally activated, and by no longer utilizing the three-way catalyst, fuel efficiency is increased. The cold start NO 2  generation system according to the present disclosure leverages the air/fuel ratio in the engine to control the temperature of the catalyst so that the temperature is hot enough to thermally activate the SCR system and discontinue use of the three-way catalyst, allowing for lean operation of the engine. 
         [0018]    Referencing  FIG. 1 , an exhaust assembly  10  according to the present disclosure includes a three-way catalyst  12 . The three-way catalyst  12  includes a hydrocarbon (HC) oxidation zone  14  and a nitrogen dioxide (NO 2 ) generation zone  16 . The exhaust assembly  10  further includes a plurality of SCR systems  18 - 1 , . . . ,  18 - n  (referred to collectively as SCR systems  18 ), temperature sensors  22 - 1 , . . . ,  22 - n  (referred to collectively as temperature sensors  22 ), a mixer  28 , and nitrogen oxides (NO x ) sensors  30 - 1 , . . . ,  30 - n  (referred to collectively as NO x  sensors  30 ). The exhaust assembly  10  is mechanically connected to an engine  34  and receives exhaust gases produced from combustion. A control module  36  receives signals from each temperature sensor  22  and NO x  sensor  30  and sends commands to the three-way catalyst  12  and SCR systems  18 . 
         [0019]    The quantity of HC present in the exhaust assembly  10  at the engine  34  start determines the size of the HC oxidation zone  14  and NO 2  generation zone  16 . The HC is oxidized before NO 2  is generated because the HC oxidizes at a much lower temperature. When the HC has been removed from the system, the NO 2  generation zone  16  can begin to generate NO 2  from NO in the emissions gases. The mixer  28  may be implemented in the exhaust assembly  10  if active urea injection is used to supply NH 3  to the SCR system  18 . The NO x  sensor  30  placed before each SCR system  18  determines the quantity of NO in the emission gas. The temperature sensor  22  placed before each SCR system  18  determines the temperature of the emission gas entering the SCR system  18 . 
         [0020]    Referring now to  FIG. 2 , the control module  36  includes a catalyst control module  38 , a diagnostic module  40 , and a fuel control module  42 . The diagnostic module  40  receives signals from the NO x  sensors  30  and temperature sensors  22  to determine the level of NO and the temperature of the gases within the exhaust assembly  10 . The diagnostic module  40  compares the temperature of the coolant with a first predetermined temperature threshold (for example only, 300° C.) to establish whether catalyst operation is optimal. Catalyst operation is optimal when the temperature of the coolant is greater than the first predetermined temperature threshold. The diagnostic module  40  provides a signal, to the catalyst control module  38 , that indicates whether catalyst operation is optimal. 
         [0021]    The diagnostic module  40  compares the temperature of the three-way catalyst  12  to a second predetermined temperature threshold and sends a signal, to the fuel control module  42 , indicating whether the temperature of the three-way catalyst  12  is greater than or less than the second predetermined temperature threshold. The second predetermined temperature threshold may be based on the optimal temperature for NO to NO 2  conversion, which is dependent on the type of catalyst used and the particular characteristics of the exhaust system. For example only, the second predetermined temperature threshold may be between 275° C. and 325° C. when a perovskite catalyst is used. The optimal temperature may vary if a different type of NO 2  generation catalyst is used. The diagnostic module  40  further compares the temperature of the NO 2  generation zone  16  to a third predetermined temperature threshold and communicates the results to the fuel control module  42 . The third predetermined temperature threshold for the NO 2  generation zone  16  may be set similarly to the second predetermined temperature threshold for the three-way catalyst  12  depending on the characteristics of the exhaust assembly  10 . For example only, the temperature threshold may be between 275° C. and 325° C. 
         [0022]    The first, second, and third predetermined temperature thresholds may either be equal to one another as described in the present disclosure, or the first, second, and third predetermined temperature thresholds may be different values or ranges of values in relation to one another if engine and exhaust parameters are varied. For example only, if a catalyst other than perovskite is used for NO to NO 2  conversion, the second predetermined temperature threshold may be a different value than the first and third predetermined temperature thresholds. 
         [0023]    The catalyst control module  38  receives signals from the diagnostic module  40  indicating whether the catalyst operation is optimal. If catalyst operation is optimal, the catalyst control module  38  determines whether the SCR system  18  is thermally activated. If catalyst operation is not optimal, the catalyst control module  38  determines the HC oxidation zone  14  and the NO 2  generation zone  16 . Determination of the HC oxidation zone  14  is a function of the amount of HC in the system, the exhaust flow, and temperature. For example only, if there is more HC in the exhaust system, the HC oxidation zone  14  will be larger in order to accommodate the catalyst volume needed to oxidize the HC in the exhaust assembly  10 . The catalyst control module  38  determines the NO 2  generation zone  16  by subtracting the volume of the HC oxidation zone  14  from the total volume of the three-way catalyst  12 . The NO 2  generation zone  16  is where NO is converted to NO 2  by using a catalyst (for example, perovskite). The catalyst facilitates the reaction of the O 2  and the NO to form NO 2 . 
         [0024]    The fuel control module  42  receives a first signal from the diagnostic module  40  if the three-way catalyst  12  temperature is greater than the first predetermined temperature threshold. The fuel control module  42  activates lean operation of the engine  34  and sends a signal to the catalyst control module  38  commanding discontinued use of the three-way catalyst  12 . The fuel control module  42  receives a second signal from the diagnostic module  40  that indicates whether the NO 2  generation zone  16  temperature is greater than or less than the third predetermined temperature threshold. If the NO 2  generation zone  16  temperature is greater than the third predetermined temperature threshold, the fuel control module  42  reduces the air/fuel (A/F) ratio (for example, engine operation becomes more rich) by an NO 2  correction factor. The NO 2  correction factor is determined by the fuel control module  42  and is a function of the difference between the temperature of the NO 2  generation zone  16  and the third predetermined temperature threshold. If the temperature of the NO 2  generation zone  16  is less than the third predetermined temperature threshold, the fuel control module  42  increases the A/F ratio (for example, engine operation becomes more lean) by the NO 2  correction factor. 
         [0025]    Referencing  FIG. 3 , a cold start NO 2  generation method  110  begins at  112  and determines whether the coolant temperature is less than the first predetermined temperature threshold. If false, the method  110  continues to  118 , and, if true, the method  110  continues to  114  and determines whether the SCR system  18  is thermally activated. 
         [0026]    At  118 , the HC oxidation zone  14  is identified, and, at  120 , the NO 2  generation zone  16  is identified. At  122 , the method  110  determines whether the an exhaust temperature in the three-way catalyst  12  is greater than the second predetermined temperature threshold. If true the method  110  continues at  126 . If false, the method  110  proceeds with catalyst warm-up at  124  and, at  118  and  120 , the HC oxidation zone  14  and NO 2  generation zone  16  are re-determined. The temperature is reevaluated to determine whether the exhaust temperature in the three-way catalyst  12  is greater than the second predetermined temperature threshold at  122 . 
         [0027]    At  126 , lean operation is activated and use of the three-way catalyst  12  is discontinued. At  128 , the method  110  determines whether the temperature of the NO 2  generation zone  16  is greater than the third predetermined temperature threshold. If true, the air/fuel ratio is increased by adding the NO 2  correction factor at  130 . The correction factor is a function of the difference between the temperature of the NO 2  generation zone and the third predetermined temperature threshold. If false, the air/fuel ratio is decreased by subtracting the NO 2  correction factor at  132 . 
         [0028]    At  114 , the method  110  determines whether the SCR system  18  is thermally activated by evaluating temperature inputs from the temperature sensor signals  22 . For example only, if the reading from the temperature sensor signals  22  indicates an exhaust gas temperature greater than 200° C., the SCR system  18  will be thermally activated. If true, the method  110  exits and the exhaust assembly  10  resumes normal operation. If false, the method  110  evaluates whether the temperature of the NO 2  generation zone  16  is greater than the third predetermined temperature threshold at  128 . The procedures at  128 ,  130 ,  132 , and  114  are repeated until the SCR system  18  becomes thermally activated and the method  110  exits. 
         [0029]    After the method  110  exits, the exhaust assembly  10  resumes normal operating conditions. The exiting of the method  110  essentially means that the exhaust assembly  10  is no longer operating in a cold start mode. For example, the three-way catalyst  12  is no longer operational for the remainder of the engine-on condition. The three-way catalyst  12  may only operate during cold start procedures. Further, the SCR system  18  continues to convert NO x  via the reaction with ammonia (NH 3 ) by either using the ammonium nitrate stored in the SCR system  18  or using injected urea, allowing the engine to run lean and have higher fuel efficiency without sacrificing emission quality. 
         [0030]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.

Technology Classification (CPC): 8