Patent Application
20130091826
The present disclosure relates to cold start emission strategies, and more particularly to maximization of NO2 generation during a cold start of an engine.
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.
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.
A cold start NO2 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 NO2 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.
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.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
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.
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.
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.
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.
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.
A cold start NO2 generation system according to the present disclosure reduces the delay by providing an NO2 generation zone within the three-way catalyst to convert nitric oxide (NO) to nitrogen dioxide (NO2) and store the NO2 in the SCR system. Accordingly, the NO2 generation zone is separated from a hydrocarbon (HC) oxidation zone that functions to oxidize hydrocarbons. The HC oxidation zone and NO2 generation zone are separated because the presence of HC prohibits NO2 generation. NO2 generation is delayed until all HC is oxidized, and lean operation cannot occur until enough NO2 forms to be stored in the SCR system.
The NO2 is oxidized to generate ammonium nitrate (ammonia, NH4NO3) according to:
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 (NH3) separately generated from the three way catalyst. The NO2 generation zone of the three-way catalyst (and the three-way catalyst as a whole) is not required to generate NO2 after the SCR system is thermally activated, and by no longer utilizing the three-way catalyst, fuel efficiency is increased. The cold start NO2 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.
Referencing
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 NO2 generation zone 16. The HC is oxidized before NO2 is generated because the HC oxidizes at a much lower temperature. When the HC has been removed from the system, the NO2 generation zone 16 can begin to generate NO2 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 NH3 to the SCR system 18. The NOx 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.
Referring now to
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 NO2 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 NO2 generation catalyst is used. The diagnostic module 40 further compares the temperature of the NO2 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 NO2 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.
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 NO2 conversion, the second predetermined temperature threshold may be a different value than the first and third predetermined temperature thresholds.
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 NO2 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 NO2 generation zone 16 by subtracting the volume of the HC oxidation zone 14 from the total volume of the three-way catalyst 12. The NO2 generation zone 16 is where NO is converted to NO2 by using a catalyst (for example, perovskite). The catalyst facilitates the reaction of the O2 and the NO to form NO2.
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 NO2 generation zone 16 temperature is greater than or less than the third predetermined temperature threshold. If the NO2 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 NO2 correction factor. The NO2 correction factor is determined by the fuel control module 42 and is a function of the difference between the temperature of the NO2 generation zone 16 and the third predetermined temperature threshold. If the temperature of the NO2 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 NO2 correction factor.
Referencing
At 118, the HC oxidation zone 14 is identified, and, at 120, the NO2 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 NO2 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.
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 NO2 generation zone 16 is greater than the third predetermined temperature threshold. If true, the air/fuel ratio is increased by adding the NO2 correction factor at 130. The correction factor is a function of the difference between the temperature of the NO2 generation zone and the third predetermined temperature threshold. If false, the air/fuel ratio is decreased by subtracting the NO2 correction factor at 132.
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 NO2 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.
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 NOx via the reaction with ammonia (NH3) 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.
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.
