Reductant Cooperative and Efficient Distribution Method and System for Double-Stage Urea Injection System

Abstract

The present invention provides a method and system for synergistic and efficient distribution of reductant for a two-stage urea injection system. Through the synergistic and efficient distribution strategy of reductant, based on the performance of SDPF and SCR in different temperature ranges, a temperature zone control strategy that is more conducive to taking into account the passive regeneration efficiency of PM on SDPF, the overall DeNOx efficiency of the two-stage SCR system, and the reductant energy efficiency ratio is determined. This control strategy is based on the accurate modeling of the thermodynamic process and chemical reaction kinetics engineering of the aftertreatment system. Aiming at the working characteristics of the aftertreatment system at different temperatures, a reductant distribution strategy is adopted to bring into play the comprehensive performance of the aftertreatment components. The present invention can effectively improve its passive regeneration performance and urea energy efficiency ratio without affecting the DeNOx efficiency of the aftertreatment system.

Description

Technical Field

[0001] The present invention relates to the technical field of reductant utilization in diesel engine aftertreatment systems, and particularly relates to a method and system for synergistic and efficient distribution of reductants for a dual-stage urea injection system. Background Art

[0002] Diesel engine exhaust contains relatively high amounts of nitrogen oxides (NO x ), and particulate matter (PM). Existing emission regulations limit the emissions of NO x and PM, and specify different levels of limits. With the further tightening of emission regulations, the weighting factors for cold start condition emissions in the corresponding emission limits have increased significantly, giving rise to the development of aftertreatment systems towards a direction of closer coupling in size and function.

[0003] NO x is a reaction product of N2 and O2 in the air inhaled by the engine into the cylinder at high temperatures, and its main components are NO and NO2. Urea selective catalytic reduction technology (abbreviated as Urea-SCR technology) is the main technology for controlling NO x emissions in engines. The most common form of this technology is: using urea aqueous solution to decompose to produce ammonia (NH3), and under the action of an SCR catalytic converter, ammonia undergoes a selective catalytic reduction reaction with NO x to generate nitrogen and water, which are then discharged into the atmosphere. By injecting different amounts of urea into the exhaust of the diesel engine, the emissions of NO x can be effectively controlled. When the temperature is lower than 187°C, the hydrolysis and pyrolysis reactions of urea cannot occur sufficiently. At the same time, the reaction rate of the SCR reaction under conditions below 250°C is significantly affected by the NO2 / NO x ratio, real-time ammonia storage amount, temperature, and space velocity.

[0004] PM is a reaction product of injected fuel, engine oil, etc. under high temperature and local oxygen deficiency conditions in the cylinder, and mainly includes soot, soluble organic matter, and sulfates. Currently, the main means of controlling particulate matter is to use a diesel particulate filter (DPF). The DPF traps most of the PM inside the carrier through a wall-flow structure, preventing it from entering the atmosphere. During the use of the DPF, PM will continuously accumulate, resulting in a gradual increase in exhaust back pressure, which will in turn affect the normal operation of the engine. Therefore, it is necessary to periodically eliminate the accumulated PM through a high-temperature oxidation reaction, and this process is called the active regeneration process. Active regeneration usually requires consuming additional fuel to increase the exhaust temperature to promote the PM to reach the oxidation conditions, thus resulting in an increase in fuel consumption.

[0005] As the aftertreatment system develops towards a more compact coupling in terms of size and function, the technology of coating SCR catalyst on the surface of DPF (SDPF) has emerged. This technology integrates the SCR reaction and particulate matter trapping in the same space, effectively reducing the size and cost of the aftertreatment system and improving the temperature response performance of the system.

[0006] To meet the more stringent requirements for emissions during the cold start phase in future emission regulations, a two-stage SCR + urea injection system is usually adopted. The front stage is placed as close as possible to the engine outlet to reach the high-efficiency reaction temperature faster. There are several technical routes for the two-stage SCR + urea injection system, such as: oxidation catalytic converter (DOC) + SDPF + SCR + ammonia oxidation catalytic converter (ASC), DOC + SCR + ASC + DPF + SCR + ASC, etc. Among them, the layout space and cost of the technical route including the SDPF system have obvious advantages, so it is widely used.

[0007] However, the application of SDPF also has the following problems. SDPF realizes the selective catalytic conversion ability of NO by coating SCR catalyst on the entire carrier surface. x However, the oxidation catalytic reaction is not selective and will directly oxidize NH3. Therefore, SDPF coated with SCR catalyst usually will not be further coated with oxidation catalyst. Since the SCR reaction will preferentially consume NO2 in the exhaust gas, the passive regeneration ability of SDPF is severely weakened and the active regeneration interval is shortened, affecting fuel consumption and the service life of the aftertreatment system. The urea distribution strategy of the traditional two-stage injection system of SDPF + SCR often focuses on the upstream SDPF, and the downstream SCR is used as a supplement when the reaction ability of the upstream SDPF is insufficient. At this time, a large amount of reducing agent reacts on the SDPF, and almost no NO2 remains. The aftertreatment systems applied with such strategies will all have a relatively short regeneration interval. Moreover, for the traditional distribution strategy of the two-stage urea distribution system, due to the concentration of urea injection at the SDPF inlet with a higher temperature under high-temperature working conditions, the injected urea is oxidized to a greater extent, and the energy efficiency ratio of the reducing agent is poor.

[0008] Facing the ultra-low emission requirements for motor vehicle pollutants and extremely strict fuel consumption regulations, both the DeNOx efficiency and the passive regeneration performance of the aftertreatment system need to be considered. The reducing agent collaborative and efficient distribution strategy of the two-stage injection system provided by the present invention takes into account both the passive regeneration of PM on SDPF and the overall DeNOx efficiency of the two-stage SCR system, which helps the engine-aftertreatment system achieve lower emission and fuel consumption targets. Summary of the Invention

[0009] Based on this, the purpose of the present invention is to propose a method and system for the coordinated and efficient distribution of reducing agents for a two-stage urea injection system, which can effectively improve its passive regeneration performance and urea energy efficiency ratio without affecting the DeNOx efficiency of the after-treatment system.

[0010] In one aspect, the present invention provides a method for synergistically and efficiently distributing a reducing agent in a dual-stage urea injection system, the method comprising:

[0011] Confirming the catalytic unit configuration of the target after-treatment system to establish a corresponding thermodynamic model and chemical reaction kinetic model for the catalytic unit. The thermodynamic model includes a convection heat transfer model, a heat conduction model, and a heat radiation model. The chemical reaction kinetic model includes a NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetic model.

[0012] Identify parameters of the thermodynamic models and chemical reaction kinetic models through small-scale experiments, including convection heat transfer coefficient, thermal conductivity, specific heat capacity, thermal radiation / heat transfer coefficient, chemical reaction activation energy, chemical reaction pre-exponential factor, and reaction temperature;

[0013] An engine test bench was built to conduct a performance test on SCR and SDPF. Based on the test results, the carrier temperatures of SCR and SDPF were divided into four continuous temperature intervals. The four temperature intervals corresponding to SCR are the DeNO x Invalid zone, SCR DeNO x The efficiency sensitive range, SCR high efficiency conversion range and SCR NH3 oxidation efficiency sensitive range, and the four temperature ranges corresponding to SDPF are SDPF DeNO x Invalid section, DeNO of SDPF x efficiency sensitive range, SDPF passive regeneration efficiency sensitive range, and SDPF NH3 oxidation efficiency sensitive range;

[0014] The current carrier temperatures of the SCR and SDPF are obtained at first preset time intervals, and a corresponding target reductant distribution strategy is executed according to the current carrier temperatures of the SCR and SDPF, so as to calculate target injection amounts of the first and second nozzles according to the target reductant strategy, where the first nozzle corresponds to the SDPF and the second nozzle corresponds to the SCR.

[0015] In summary, according to the above-described method for synergistic and efficient distribution of reductant for a dual-stage urea injection system, by means of a synergistic and efficient reductant distribution strategy based on the performance of SDPF and SCR in different temperature ranges, a temperature zone control strategy that is more conducive to taking into account the passive regeneration efficiency of PM on SDPF, the overall DeNOx efficiency of the dual-stage SCR system, and the reductant energy efficiency ratio is determined. This control strategy is based on an accurate modeling of the thermodynamic process and chemical reaction kinetics engineering of the aftertreatment system. For the working characteristics of the aftertreatment system at different temperatures, an efficient reductant distribution strategy is adopted to give full play to the comprehensive performance of the aftertreatment components. This helps the engine-aftertreatment system achieve lower emission and energy consumption targets.

[0016] In a preferred embodiment of the present invention, the step of obtaining the current carrier temperatures of SCR and SDPF every first preset time and executing a corresponding target reductant distribution strategy according to the current carrier temperatures of SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy, where the first nozzle corresponds to SDPF and the second nozzle corresponds to SCR includes:

[0017] When it is monitored that the SDPF carrier temperature enters the DeNOx efficiency sensitive zone of SDPF, switch to the Class A reductant supply control state. At this time, using the real-time NH3 storage amount signal, SDPF inlet NO2 concentration signal, SDPF carrier temperature signal, SDPF inlet NO x concentration signal, exhaust mass flow signal, and inlet NH3 concentration signal as inputs, calculate the real-time NH3 storage amount, the real-time DeNO x efficiency of the SDPF catalyst, the SDPF outlet NO x concentration, SDPF outlet NO2 concentration, and SDPF outlet NH3 concentration by using the established SCR chemical reaction kinetics model of SDPF;

[0018] Update the real-time NH3 storage amount as an input to the model, and calculate the urea injection amount requirement value of the first nozzle according to the real-time DeNO x efficiency of the SDPF catalyst;

[0019] Combine the SDPF outlet NO x concentration, SDPF outlet NO2 concentration, and SDPF outlet NH3 concentration with the SCR real-time NH3 storage amount, SCR carrier temperature, and exhaust mass flow as inputs to the model, and calculate the DeNO x efficiency of the SCR catalyst through the SCR chemical reaction kinetics model, so as to calculate the urea injection amount requirement value of the second nozzle according to the DeNO x efficiency of the SCR catalyst.

[0020] In a preferred embodiment of the present invention, the steps of obtaining the current carrier temperatures of the SCR and SDPF every first preset time, and executing a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy, where the first nozzle corresponds to the SDPF and the second nozzle corresponds to the SCR further include:

[0021] When it is monitored that the SDPF carrier temperature enters the passive regeneration efficiency sensitive area of the SDPF, the system will switch to the Class B reductant supply control state;

[0022] Judge the temperature range in which the SCR is located according to the current carrier temperature of the SCR, obtain the corresponding target correction coefficient from the preset data table according to the temperature range in which the SCR is located, and according to the product of the target correction coefficient and the maximum DeNO x efficiency of the SCR catalyst to obtain the target DeNO x efficiency of the SCR catalyst;

[0023] Calculate the target DeNO x concentration at the inlet of the SCR catalyst according to the concentration limit value of the tail pipe NOx emission, and according to the exhaust mass flow rate, the target DeNO x concentration at the inlet of the SCR catalyst, and the DeNO x concentration at the inlet of the SDPF to calculate the urea injection amount requirement value of the first nozzle;

[0024] Calculate the urea injection amount requirement value of the second nozzle according to the exhaust mass flow rate, the target DeNO x efficiency of the SCR catalyst, and the target DeNO x concentration at the inlet of the SCR catalyst.

[0025] In a preferred embodiment of the present invention, if the maximum DeNOx efficiency of the SCR catalyst is ηSCR_Max, then the NO x emission concentration C NOxSDPFDs_Lim satisfies the following relationship:

[0026] C NOxSDPFDs_Lim ≤ C NOxTp_Lim / (1 - η SCR_Max × f )

[0027] C NOxTp_Lim is the control limit value, and f is the correction coefficient.

[0028] In a preferred embodiment of the present invention, the step of obtaining the current carrier temperatures of the SCR and SDPF every first preset time and executing corresponding target reductant distribution strategies according to the current carrier temperatures of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy, where the first nozzle corresponds to the SDPF and the second nozzle corresponds to the SCR further includes:

[0029] When it is monitored that the SDPF carrier temperature enters the NH3 oxidation efficiency sensitive area of the SDPF, the system will switch to the Class C reductant supply control state;

[0030] Calculate the maximum conversion ability of the SCR at the current temperature and space velocity through the downstream SCR chemical reaction kinetics model, and calculate the urea injection amount of the second nozzle based on the NO x concentration at the engine outlet and the exhaust mass flow rate;

[0031] Calculate the urea injection amount of the first nozzle according to the NO x target conversion amount of the SDPF catalyst.

[0032] On the other hand, the present invention also proposes a reductant cooperative and efficient distribution system for a dual-stage urea injection system, and the system includes:

[0033] A model construction module for confirming the catalytic unit composition of the target after-treatment system, so as to establish corresponding thermodynamic models and chemical reaction kinetics models for the catalytic units. The thermodynamic models include a convective heat transfer model, a heat conduction model, and a thermal radiation model, and the chemical reaction kinetics models include a NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetics model;

[0034] A parameter identification module for completing the parameter identification of each of the thermodynamic models and each chemical reaction kinetics model through small-scale tests. The parameters include the convective heat transfer coefficient, the thermal conductivity, the specific heat capacity, the thermal radiation / heat transfer coefficient, the chemical reaction activation energy, the chemical reaction pre-exponential factor, and the reaction temperature;

[0035] A temperature zone division module for building an engine test bench to conduct performance baseline tests on the SCR and SDPF, and dividing the carrier temperatures of the SCR and SDPF into four consecutive temperature zones according to the results of the baseline tests. The four temperature zones corresponding to the SCR are the DeNO x ineffective zone of the SCR, the DeNO x efficiency sensitive zone of the SCR, the high-efficiency conversion zone of the SCR, and the NH3 oxidation efficiency sensitive zone of the SCR. The four temperature zones corresponding to the SDPF are the DeNO x ineffective zone of the SDPF, the DeNO xThe efficiency sensitive range, the passive regeneration efficiency sensitive range of the SDPF, and the NH3 oxidation efficiency sensitive range of the SDPF;

[0036] An injection control module, configured to obtain the current carrier temperatures of the SCR and the SDPF every first preset time, and execute corresponding target reductant distribution strategies according to the current carrier temperatures of the SCR and the SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy, where the first nozzle corresponds to the SDPF and the second nozzle corresponds to the SCR.

[0037] In a preferred embodiment of the present invention, the injection control module further includes:

[0038] A first control state execution unit, configured to switch to a Class A reductant supply control state when it is monitored that the SDPF carrier temperature enters the DeNOx efficiency sensitive area of the SDPF. At this time, the real-time NH3 storage amount signal, the SDPF inlet NO2 concentration signal, the SDPF carrier temperature signal, the SDPF inlet NO x concentration signal, the exhaust mass flow signal, and the inlet NH3 concentration signal are used as inputs, and the real-time NH3 storage amount, the real-time DeNO x efficiency of the SDPF catalyst, the SDPF outlet NO x concentration, the SDPF outlet NO2 concentration, and the SDPF outlet NH3 concentration are calculated by using the established SCR chemical reaction kinetics model of the SDPF;

[0039] A first injection demand calculation unit, configured to update the real-time NH3 storage amount therein as an input of the model, and calculate the urea injection amount demand value of the first nozzle according to the real-time DeNO x efficiency of the SDPF catalyst;

[0040] A second injection demand calculation unit, configured to use the SDPF outlet NO x concentration, the SDPF outlet NO2 concentration, and the SDPF outlet NH3 concentration, combined with the SCR real-time NH3 storage amount, the SCR carrier temperature, and the exhaust mass flow, as inputs of the model, and calculate the DeNO x efficiency of the SCR catalyst through the SCR chemical reaction kinetics model, so as to calculate the urea injection amount demand value of the second nozzle through the DeNO x efficiency of the SCR catalyst.

[0041] In a preferred embodiment of the present invention, the injection control module further includes:

[0042] A second control state execution unit, configured to switch the system to a Class B reductant supply control state when it is monitored that the SDPF carrier temperature enters the passive regeneration efficiency sensitive area of the SDPF;

[0043] Determine the temperature range in which the SCR is located based on the current carrier temperature of the SCR, obtain the corresponding target correction coefficient from a preset data table according to the temperature range in which the SCR is located, and obtain the target DeNO of the SCR catalyst based on the product of the target correction coefficient and the maximum DeNO x efficiency x of the SCR catalyst;

[0044] A first injection demand calculation unit for calculating the target DeNO at the inlet of the SCR catalyst according to the concentration limit value of the tailpipe NOx emission x concentration, and calculating the urea injection demand value of the first nozzle according to the exhaust gas mass flow rate, the target DeNO at the inlet of the SCR catalyst x concentration, and the DeNO at the inlet of the SDPF x concentration;

[0045] A second injection demand calculation unit for calculating the urea injection demand value of the second nozzle according to the exhaust gas mass flow rate, the target DeNO of the SCR catalyst x efficiency, and the target DeNO at the inlet of the SCR catalyst x concentration;

[0046] In a preferred embodiment of the present invention, the system further includes:

[0047] An emission concentration calculation module for, if the maximum DeNOx efficiency of the SCR catalyst is ηSCR_Max, then the NO at the outlet of the SDPF x emission concentration C NOxSDPFDs_Lim satisfies the following relationship:

[0048] C NOxSDPFDs_Lim ≤ C NOxTp_Lim / (1 - η SCR_Max × f )

[0049] C NOxTp_Lim is the control limit value, and f is the correction coefficient

[0050] In a preferred embodiment of the present invention, the injection control module further includes:

[0051] A third control state execution unit for, when it is monitored that the SDPF carrier temperature enters the NH3 oxidation efficiency sensitive area of the SDPF, the system will switch to the C-type reducing agent supply control state;

[0052] The second injection demand calculation unit is configured to calculate the maximum conversion capacity of SCR at the current temperature and space velocity through a downstream SCR chemical reaction kinetics model, and calculate the urea injection amount of the second nozzle based on the NO concentration at the engine outlet and the exhaust mass flow rate; x

[0053] The first injection demand calculation unit is configured to calculate the urea injection amount of the first nozzle according to the target conversion amount of NO by the SDPF catalyst. x

[0054] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 FIG. is a flowchart of a method for synergistic and efficient distribution of reducing agents for a dual-stage urea injection system according to the first embodiment of the present invention;

[0056] Figure 2 FIG. is a schematic diagram of the hardware environment corresponding to the preferred embodiment;

[0057] Figure 3 FIG. is a flowchart of the implementation of the synergistic and efficient distribution strategy of reducing agents for a dual-stage urea injection system;

[0058] Figure 4 FIG. is a schematic diagram of the SDPF temperature range division;

[0059] Figure 5 FIG. is a schematic diagram of the SCR temperature range division;

[0060] Figure 6 FIG. is a prediction flowchart for predicting the NO2 ratio at the DOC outlet;

[0061] Figure 7 FIG. is a control state diagram of the reducing agent supply when the SDPF carrier temperature is in different temperature ranges;

[0062] Figure 8 FIG. is a urea injection control strategy diagram under the A-type reducing agent supply control state;

[0063] Figure 9 FIG. is a urea injection control strategy under the B-type reducing agent supply control state;

[0064] Figure 10 FIG. is a urea injection control strategy diagram under the C-type reducing agent supply control state;

[0065] Figure 11 FIG. is a schematic structural diagram of a system for synergistic and efficient distribution of reducing agents for a dual-stage urea injection system according to the second embodiment of the present invention. ​​

[0066] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0067] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0069] See also Figure 3 The method for efficiently distributing reducing agents in a dual-stage urea injection system according to the present invention mainly includes the following steps:

[0070] Step (1) establishes a carrier temperature prediction model for the DOC, SDPF, and SCR to achieve carrier temperature prediction for the DOC, SDPF, and SCR. The SDPF and SCR carrier temperature prediction models primarily model the following thermodynamic processes: 1) convective heat transfer between the exhaust and the catalyst; 2) heat conduction within the catalyst; and 3) radiation heat transfer from the catalyst housing to the atmosphere. In addition to the thermodynamic components, the DOC carrier temperature prediction model also considers the further oxidation heat release of HC on the DOC and establishes a corresponding HC oxidation heat release correction model.

[0071] Step (2) will establish a kinetic model of the NO oxidation reaction of DOC to predict the NO2 ratio at the DOC outlet.

[0072] Step (3) will establish the SCR chemical reaction kinetic model of SDPF and SCR catalyst to calculate the DeNOx reaction process occurring on SDPF and SCR respectively;

[0073] Step (4) Through the performance test of SDPF, four continuous temperature ranges are divided based on the carrier temperature of SDPF, namely, SDPF DeNOx invalid range, SDPF DeNOx efficiency sensitive range, SDPF passive regeneration efficiency sensitive range and SDPF NH3 oxidation efficiency sensitive range.

[0074] Step (5): Through the performance baseline test of the SCR, four consecutive temperature ranges, namely the DeNOx ineffective range of the SCR, the DeNOx efficiency sensitive range of the SCR, the high-efficiency conversion range of the SCR, and the NH3 oxidation efficiency sensitive range of the SCR, are divided based on the carrier temperature of the SCR.

[0075] Step (6): The carrier temperatures of the SDPF and SCR will be monitored in real time, and based on this, the control target of the reductant distribution strategy will be adjusted. When it is monitored that the carrier temperature of the SDPF is in the DeNOx ineffective range of the SDPF, the reductant supply control system will not supply reductant; when it is monitored that the carrier temperature of the SDPF enters the DeNOx efficiency sensitive area of the SDPF, the system will switch to the Class A reductant supply control state; when it is monitored that the carrier temperature of the SDPF enters the passive regeneration efficiency sensitive area of the SDPF, the system will switch to the Class B reductant supply control state; when it is monitored that the carrier temperature of the SDPF enters the NH3 oxidation efficiency sensitive area of the SDPF, the system will switch to the Class C reductant supply control state

[0076] Step (7): Once it is monitored that the system enters the Class A reductant supply control state, the upstream reductant supply rate will be allocated with the DeNOx efficiency of the SDPF as the main control target. If the DeNOx efficiency of the SDPF is insufficient, it will be supplemented by the downstream SCR;

[0077] Step (8): When it is monitored that the system enters the Class B reductant supply control state, the basic control target will be switched to: under the condition that the tailpipe NOx emissions do not exceed the limit value, the passive regeneration efficiency of the SDPF will be increased as much as possible. At this time, it is necessary to judge the inlet state of the downstream SCR. When the SCR carrier temperature is in different temperature zones, different DeNOx capacity correction coefficients should be used to control the DeNOx ratio borne by the downstream to avoid the situation where the downstream SCR cannot completely convert the NOx at the outlet of the SDPF and cause the emissions to exceed the regulatory limit;

[0078] Step (9): Once it is monitored that the system enters the Class C reductant supply control state, since the oxidation degree of NH3 injected at the inlet of the SDPF will increase with the increase of temperature, it is necessary to minimize the reductant injection amount at the inlet of the SDPF. Therefore, the control strategy takes the downstream DeNOx efficiency as the primary implementation goal. Each individual DeNOx system in the dual-injection system usually does not have a large degree of redundant design. At this time, the downstream SCR may not have the volume to completely eliminate the engine outlet NOx emissions. Therefore, when entering the NH3 oxidation efficiency sensitive area of the SDPF, the operation logic of the control system is: first calculate the maximum conversion capacity of the SCR at the current temperature and space velocity through the downstream SCR chemical reaction kinetics model, and then calculate the reductant supply amount at the inlet of the SDPF based on this;

[0079] In summary, the method proposed by the present invention first confirms the composition of the catalytic unit of the target post-treatment system; then, a corresponding thermodynamic model and a chemical reaction kinetics model are established for the target catalytic unit, and the parameter identification of the thermodynamic model and the chemical reaction kinetics model is completed through a small-scale test; the temperature range of the 1# catalytic converter and the 2# catalytic converter is divided through the performance test results carried out on the engine test bench; the temperature of the SDPF carrier is monitored in real time. If the temperature of the SDPF carrier is in the DeNOx ineffective range, then no reductant supply is required at this time; if the temperature of the SDPF carrier is in the DeNOx efficiency sensitive range, then a Class A reductant supply control strategy with the main control objective of fully realizing the DeNOx capacity of the 1# catalytic converter is adopted at this time; if the temperature of the SDPF carrier is in the passive regeneration efficiency sensitive range, then a Class B reductant supply control strategy is adopted at this time. Under the condition that the NO x emission at the tail pipe does not exceed the limit value, the passive regeneration efficiency of the DPF is increased as much as possible. Under the Class B reductant supply control state, it is also necessary to determine different DeNOx capacity correction coefficients based on the temperature range of the 2# catalytic converter to complete the calculation of the target injection amounts of the two nozzles; if the temperature of the SDPF carrier is in the NH3 oxidation efficiency sensitive range, then a Class C reductant supply control strategy with the main control objective of fully realizing the DeNOx capacity of the 2# catalytic converter is adopted at this time.

[0080] The beneficial effect of the present invention is that without affecting the DeNOx efficiency of the post-treatment system, the passive regeneration performance and the reductant energy efficiency ratio are effectively improved.

[0081] It should be further noted that the SDPF carrier surface is usually only coated with an SCR catalyst, and the SCR reaction will preferentially consume NO2 in the exhaust gas, resulting in a serious weakening of the passive regeneration ability of the SDPF and a shortening of the active regeneration interval, which affects the fuel consumption and the service life of the post-treatment system. The urea distribution strategy of the traditional two-stage injection system of SDPF+SCR often focuses on the upstream SDPF, and the downstream SCR is used as a supplement when the reaction ability of the upstream SDPF is insufficient. At this time, a large amount of reductant reacts on the SDPF, and almost no NO2 remains, greatly affecting the passive regeneration performance of the SDPF. The post-treatment systems applying such strategies will all have a relatively short regeneration interval. In addition, due to the concentration of the urea injection amount at the SDPF inlet with a higher temperature under high-temperature conditions in the traditional distribution strategy of the two-stage urea distribution system, the injected urea is oxidized to a greater extent, and the reductant energy efficiency ratio is poor.

[0082] The reducing agent collaborative and efficient distribution strategy provided by the present invention is based on the performance of SDPF and SCR in different temperature ranges, and determines a temperature zoning control strategy that is more conducive to taking into account the passive regeneration efficiency of PM on SDPF, the overall DeNOx efficiency of the two-stage SCR system, and the reducing agent energy efficiency ratio. This control strategy is based on the accurate modeling of the thermodynamic process and chemical reaction kinetics of the aftertreatment system. For the working characteristics of the aftertreatment system at different temperatures, an efficient reducing agent distribution strategy is adopted to give full play to the comprehensive performance of the aftertreatment components. It helps the engine-aftertreatment system achieve lower emission and energy consumption targets.

[0083] Please refer to Figure 2 , the aftertreatment system corresponding to the preferred embodiment of the present invention is the DOC+SDPF+SCR+ASC scheme, which is matched with a two-stage urea injection system. The exhaust gas oxidizes reducing gases such as HC and CO through the oxidation catalysis of DOC. At the same time, NO can also further react with O2 on DOC to generate NO2. When the temperature of the SDPF carrier exceeds the critical temperature for urea injection start, the 1# urea nozzle (the first nozzle) starts to inject urea. The injected urea undergoes pyrolysis and hydrolysis reactions under the heating of the exhaust gas to generate NH3. NH3 rapidly reacts with NOx under the action of the SCR catalyst coated on SDPF to generate N2 and H2O. If the urea injection amount is insufficient, the remaining NOx will continue to flow downstream. If the urea injection amount is excessive, the remaining NH3 will flow downstream; the downstream SCR acts as a redundant DeNOx system to undertake the remaining NOx conversion work, and the 2# urea nozzle (the second nozzle) supplies the required reducing agent. The SCR system can be arranged away from the SDPF to obtain a larger temperature difference. In this arrangement, if the temperature of the upstream SDPF is too high, resulting in a decrease in the conversion efficiency, the downstream SCR can still achieve excellent DeNOx performance due to this temperature difference to ensure the overall conversion efficiency of the system. The reducing agent supply system of the entire aftertreatment system uses urea aqueous solution with a mass concentration of 32.5% as the reducing agent. Among them, the ECU and DCU can be independent hardware structures or combined into a complete control unit. The ECU and DCU collect engine speed, engine fuel injection volume, intake air temperature, intake air pressure, intake air mass flow rate, EGR valve opening degree, coolant temperature, DOC catalyst upstream temperature sensor, SDPF catalyst upstream temperature sensor, SCR catalyst upstream temperature sensor, SCR catalyst downstream temperature sensor, DOC catalyst upstream NO x concentration sensor, SCR catalyst upstream NO x concentration sensor, SCR catalyst downstream NO xSignals sent by concentration sensors, urea level sensors, etc. complete the coordinated and efficient distribution of reductants for the dual-injection system through the calculations of corresponding control function modules, achieving the goal of simultaneously optimizing the passive regeneration performance of PM on the SDPF and enhancing the overall DeNOx efficiency of the dual-stage SCR system.

[0084] Please refer to Figure 1 , which shows a flowchart of a method for the coordinated and efficient distribution of reductants for a dual-stage urea injection system in the first embodiment of the present invention. The method includes steps S01 to S04, where:

[0085] Step S01: Confirm the catalytic unit composition of the target after-treatment system, and establish corresponding thermodynamic models and chemical reaction kinetic models for the catalytic unit;

[0086] Among them, the thermodynamic model includes a convective heat transfer model, a heat conduction model, and a thermal radiation model, and the chemical reaction kinetic model includes a NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetic model.

[0087] Specifically, please refer to Figure 6 , first, determine the relationship between the NO2 / NOx ratio at the engine outlet and the engine fuel injection volume, engine speed, and EGR rate through experiments and obtain the NO2 / NOx ratio MAP at the engine outlet. When the system is working, the basic NO2 / NOx ratio at the engine outlet can be obtained by looking up the NO2 / NOx ratio MAP at the engine outlet through the engine fuel injection volume, engine speed, and EGR rate, and a more accurate NO2 / NOx ratio at the engine outlet can be obtained after correction by the coolant water temperature, intake air temperature, and intake air pressure as one of the inputs of the NO oxidation reaction kinetic model of the DOC;

[0088] Second, establish a DOC carrier temperature prediction model including an HC oxidation heat release model and a thermodynamic process model. The DOC carrier temperature obtained through this model will be used as one of the inputs of the NO oxidation reaction kinetic model of the DOC.

[0089] When the catalytic performance of the DOC is determined, the inlet temperature and the exhaust gas mass flow rate determine the degree of occurrence of the HC oxidation reaction, and the post-injection fuel volume determines the total heat that can be released when the HC oxidation reaction occurs completely. Therefore, the HC oxidation heat release correction model established in the present invention takes the engine post-injection fuel volume, engine speed, exhaust gas mass flow rate, and DOC inlet temperature as inputs, and calculates the heat release rate of the HC oxidation reaction in real time. The calculated heat release rate of the HC oxidation reaction is used as the energy source of the exhaust gas to input the thermodynamic process model to complete the accurate prediction of the DOC carrier temperature;

[0090] Among them, the post-injection fuel quantity of the engine, the engine speed, and the DOC inlet temperature are obtained by the engine control unit (ECU) calculating the injection pulse width signal, the rotational speed sensor signal, and the exhaust gas temperature sensor signal at the DOC inlet respectively. The exhaust gas mass flow rate is calculated by the ECU from the intake air mass flow sensor signal and the fuel injection quantity signal.

[0091] The thermodynamic process model of the DOC mainly models the following thermodynamic processes: 1) Convective heat transfer between the exhaust gas and the catalyst; 2) Heat conduction inside the catalyst; 3) Radiative heat transfer from the catalytic converter housing to the atmosphere. The model description method is as follows:

[0092] 1) The convective heat transfer amount between the exhaust gas and the catalyst per unit time can be calculated by the following formula

[0093]

[0094] In the formula: h is the heat transfer coefficient of convective heat transfer between the exhaust gas and the catalyst, W / (m 2 •K); T P is the exhaust gas temperature, K; T C is the catalyst temperature, K; A H-T is the total surface area of the catalyst that can be in contact with the exhaust gas. It is expressed by indicating the porosity of the catalyst (i.e., the volume ratio of the exhaust gas that can flow through in the nominal volume of the unit catalyst, %), S cat indicating the internal surface area of the catalyst per unit volume of the gas that can flow through the catalyst, m 2 / m 3 . Among them A H-T can be expressed as:

[0095]

[0096] In the formula: is the radius of the cross-section of the catalyst, m; L C is the length of the catalytic converter, m; i.e., the total volume of the catalyst V C ; i.e., the total cross-sectional area of the catalyst A f ; represents the area blocked by the catalyst for the exhaust gas. The area blocked by the catalyst for the exhaust gas is very small and can be ignored. Therefore, the above formula can be expressed as

[0097]

[0098] 2) The heat conduction inside the catalyst can be derived from Fourier's law. The heat transferred through heat conduction by the catalyst per unit time is as follows:

[0099]

[0100] 3) The radiative heat transfer between the catalytic converter housing and the atmosphere can be calculated based on the Stefan - Boltzmann law:

[0101]

[0102] Where: is the radiative area between the catalytic converter and the outside; m 2 ; is the emissivity; is the gas radiation constant, W / m 2 K 4 ; T amb is the ambient temperature, K;

[0103] After the carrier temperature prediction model is established, parameter identification needs to be completed through small - scale catalyst tests. Among them, the thermodynamic parameter identification is mainly achieved by conducting step - wise temperature rise tests. Standard exhaust gases with temperatures of 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 500 °C, and 600 °C are introduced in sequence. Before reaching thermal equilibrium each time, the exhaust gas temperature remains unchanged, and at the same time, the relationship curves of the catalyst carrier temperature at different positions with time, the carrier radiative heat release rate, etc. are recorded; The thermodynamic parameters to be confirmed are: the effective flow volume of the carrier V 、the effective cross - sectional area of the carrier A fr 、the convective heat transfer coefficient h 、the thermal conductivity λ 、the effective heat transfer area A H-T_ 、the thermal radiation area A Rad 、the specific heat capacity of the carrier .

[0104] Finally, establish the NO oxidation reaction kinetic model for the DOC. This model takes the DOC inlet NO x concentration, inlet O2 concentration, inlet NO2 / NOx ratio, DOC carrier temperature, and exhaust gas mass flow rate as inputs, and calculates the NO oxidation reaction rate occurring on the DOC. Among them, the DOC inlet NO xThe concentration is obtained through the NOx sensor signal arranged at the DOC inlet or the engine NOx emission model; the O2 concentration at the DOC inlet is obtained through the engine combustion model or the oxygen sensor or the NOx sensor at the DOC inlet; the NO2 / NOx ratio at the DOC inlet is obtained by looking up the table of engine fuel injection amount, speed and EGR rate, and is obtained by adding corrections for cooling water temperature, intake air temperature and intake pressure; the DOC carrier temperature comes from the output result of the DOC carrier temperature prediction model.

[0105] The NO oxidation reaction kinetic model of DOC only considers the reaction process of NO oxidation under aerobic conditions. The chemical reaction equation of NO oxidation reaction is: 2NO + O 2 ßà2NO 2 , the corresponding reaction rate description equation is:

[0106]

[0107] The NO oxidation reaction kinetic model of DOC outputs the outlet NO2 / NO in real time x Signal, outlet O2 concentration signal, outlet NO2 concentration signal, complete the NO2 concentration and NO2 / NO of the DOC part x Proportional forecast.

[0108] Step S02: completing parameter identification of each of the thermodynamic models and each of the chemical reaction kinetic models through small sample tests;

[0109] The parameters include convection heat transfer coefficient, thermal conductivity, specific heat capacity, thermal radiation / heat transfer coefficient, chemical reaction activation energy, chemical reaction pre-exponential factor, and reaction temperature;

[0110] Step S03: Building an engine test bench to conduct a performance test on the SCR and SDPF, and dividing the carrier temperatures of the SCR and SDPF into four continuous temperature intervals based on the test results;

[0111] Among them, the four temperature ranges corresponding to SCR are SCR DeNO x Invalid zone, SCR DeNO x The efficiency sensitive range, SCR high efficiency conversion range and SCR NH3 oxidation efficiency sensitive range, and the four temperature ranges corresponding to SDPF are SDPF DeNO x Invalid section, DeNO of SDPF x efficiency sensitive range, SDPF passive regeneration efficiency sensitive range, and SDPF NH3 oxidation efficiency sensitive range;

[0112] Specifically, see Figure 4, according to the working characteristics of the selected SDPF system, the working state of SDPF is divided into 4 temperature ranges according to the carrier temperature, namely: the DeNOx ineffective range of SDPF, the DeNOx efficiency sensitive range of SDPF, the passive regeneration efficiency sensitive range of SDPF, and the NH3 oxidation efficiency sensitive range of SDPF.

[0113] Among them, the DeNOx ineffective range of SDPF is determined by the lowest temperature at which the hydrolysis and pyrolysis reactions of urea can occur, so the temperature range is (-273°C, 185°C);

[0114] The DeNOx efficiency sensitive temperature range of SDPF is obtained by conducting DeNOx efficiency tests of SDPF under different temperatures, space velocities, ammonia storage amounts, and NO2 / NO x ratios. When the SDPF carrier temperature is higher than 250°C, the DeNOx efficiency on SDPF no longer increases with the increase of temperature, and the space velocity, ammonia storage amount, and NO2 / NO x ratio no longer affect the DeNOx efficiency. Therefore, the temperature range of the DeNOx efficiency sensitive temperature range is set as [185°C, 250°C);

[0115] The passive regeneration efficiency sensitive temperature range of SDPF is obtained through SDPF passive regeneration rate tests under different temperatures, space velocities, carbon loadings, and NO2 / NO x ratios. When the SDPF carrier temperature exceeds 250°C, the reaction between NO2 and PM begins to occur. When the temperature exceeds 350, the reaction rate of O2 and PM is equivalent to that of NO2 and PM. The passive regeneration reaction rate after this temperature is less affected by the NO2 concentration. Therefore, the temperature range of the passive regeneration efficiency sensitive temperature range is set as [250°C, 350°C);

[0116] The NH3 oxidation efficiency sensitive temperature range of SDPF is obtained by conducting DeNOx efficiency tests of SDPF under different temperatures and space velocities. When the SDPF carrier temperature is higher than 350°C, the NH3 oxidation phenomenon on SDPF begins to appear, and with the increase of temperature, the degree of NH3 oxidation increases. Therefore, the NH3 oxidation efficiency sensitive temperature range of SDPF is set as [350°C, +∞);

[0117] The actual working characteristics of SDPF cannot ensure that the division of the above temperature ranges is continuous on the entire temperature axis. However, to meet the control requirements, the division of the SDPF temperature ranges should be seamlessly connected. Therefore, the present invention selects Figure 2 the shown temperature range division method only as the preferred implementation mode of the present invention.

[0118] Please refer to Figure 5, according to the working characteristics of the selected SCR system, the working state of SCR is divided into 4 temperature ranges according to the carrier temperature. They are: the DeNOx ineffective range of SCR, the DeNOx efficiency sensitive range of SCR, the high-efficiency conversion range of SCR, and the NH3 oxidation efficiency sensitive range of SCR.

[0119] Among them, the DeNOx ineffective range of SCR is determined by the lowest temperature at which the hydrolysis and pyrolysis reactions of urea can occur, so the temperature range is (-273°C, 185°C);

[0120] The DeNOx efficiency sensitive temperature range, the high-efficiency conversion range, and the NH3 oxidation efficiency sensitive temperature range of SCR are obtained by conducting DeNOx efficiency tests of SCR under different temperature, space velocity, ammonia storage amount, and NO2 / NO x ratio conditions. When the SCR carrier temperature is higher than 250°C, the DeNOx efficiency on SCR no longer increases with the increase of temperature, and the space velocity, ammonia storage amount, and NO2 / NO x ratio no longer affect the DeNOx efficiency. Therefore, the temperature range of the DeNOx efficiency sensitive temperature range is set as [185°C, 250°C); when the SCR carrier temperature is higher than 350°C, the NH3 oxidation phenomenon on SCR begins to appear, and with the increase of temperature, the degree of NH3 oxidation occurrence increases. Therefore, the NH3 oxidation efficiency sensitive temperature range of SCR is set as [350°C, +∞);

[0121] The actual working characteristics of SCR cannot ensure that the division of the above temperature ranges is continuous on the entire temperature axis. However, to meet the control requirements, the division of the SCR temperature range should be seamlessly connected. Therefore, the present invention selects Figure 3 the shown temperature range division method only as the preferred implementation manner of the present invention.

[0122] Step S04: Obtain the current carrier temperatures of SCR and SDPF every first preset time, and execute the corresponding target reductant distribution strategy according to the current carrier temperatures of SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy;

[0123] Among them, the first nozzle corresponds to SDPF, and the second nozzle corresponds to SCR.

[0124] Please refer to Figure 7, the establishment of the SDPF carrier temperature model is similar to that of the DOC carrier temperature model, but only the thermodynamics part needs to be considered and the heat release of the HC oxidation reaction does not need to be considered. This model takes the measured values of the SDPF inlet temperature sensor, the SDPF outlet temperature sensor, and the exhaust mass flow signal as inputs. After model calculation, the SDPF carrier temperature can be obtained. When it is monitored that the SDPF carrier temperature is in the DeNOx invalid interval of the SDPF, the reductant supply control system will not supply reductant; when it is monitored that the SDPF carrier temperature enters the DeNOx efficiency sensitive area of the SDPF, the system will switch to the Class A reductant supply control state; when it is monitored that the SDPF carrier temperature enters the passive regeneration efficiency sensitive area of the SDPF, the system will switch to the Class B reductant supply control state; when it is monitored that the SDPF carrier temperature enters the NH3 oxidation efficiency sensitive area of the SDPF, the system will switch to the Class C reductant supply control state.

[0125] Please refer to Figure 8 , when the system enters the Class A reductant supply control state, the upstream reductant supply rate is allocated with the DeNOx efficiency on the SDPF as the main control target. If the DeNOx efficiency of the SDPF is insufficient, it will be supplemented by the downstream SCR; the DeNOx efficiency sensitive area of the SDPF is generally in the range of 180 - 250 °C. At this time, the reductant can start to be injected, and the SCR reaction efficiency is greatly affected by temperature, space velocity, ammonia storage amount, and NO2 / NO x ratio. And at this time, the SDPF carrier temperature is relatively low, and passive regeneration hardly has reaction conditions. Therefore, the control target of the reductant supply strategy is to maximize the DeNOx efficiency on the SDPF.

[0126] Under this control strategy, the control system first takes the real-time ammonia storage amount signal, the SDPF inlet NO2 concentration signal, the SDPF carrier temperature signal, the SDPF inlet NO x concentration signal, the exhaust mass flow signal, and the inlet NH3 concentration signal as inputs, and uses the established SCR chemical reaction kinetics model of the SDPF to calculate the real-time ammonia storage amount, the real-time DeNO x efficiency of the SDPF catalyst, the SDPF outlet NO x concentration, the SDPF outlet NO2 concentration, and the SDPF outlet NH3 concentration.

[0127] Among them, the real-time ammonia storage amount is used as the update of the model input; the urea injection amount demand value of the No. 1 nozzle can be calculated through the real-time DeNO x efficiency of the SDPF catalyst; the SDPF outlet NO xThe concentration, the NO2 concentration at the SDPF outlet, and the NH3 concentration at the SDPF outlet, together with the real-time NH3 storage amount in the SCR, the SCR carrier temperature, and the exhaust gas mass flow rate, are used as inputs. Through the SCR chemical reaction kinetics model, the DeNO x efficiency of the SCR catalyst is calculated to obtain the required value of the urea injection amount of the No. 2 nozzle.

[0128] Please refer to Figure 9 , when the system enters the control state of Class B reductant supply control, the passive regeneration efficiency on the SDPF will be introduced as a control target. At the same time, it is also necessary to judge the downstream SCR carrier temperature range. Corresponding to different SCR carrier temperature ranges, different correction coefficients need to be introduced for the maximum DeNOx efficiency of the model f , in this embodiment, the f of the DeNOx ineffective range of the SCR = 0, the f of the DeNOx efficiency sensitive range of the SCR = 0.5, the f of the high-efficiency conversion range of the SCR = 0.9, the f of the NH3 oxidation efficiency sensitive range of the SCR = 1.0;

[0129] The following takes the SCR being in the DeNOx efficiency sensitive range under the Class B reductant supply control state as an example to describe the current urea injection control strategy. When the SCR is in the DeNOx efficiency sensitive range, in order to avoid the situation that the downstream SCR cannot completely convert the NOx at the SDPF outlet and cause emissions to exceed the regulatory limit, usually only let the downstream SCR bear 50% of its current maximum DeNOx conversion target; if the maximum DeNOx efficiency of the SCR at this time is η SCR_Max , the control limit under this target working condition is C NOxTp_Lim then the NOx emission concentration at the SDPF outlet C NOxSDPFDs_Lim should satisfy the following relationship:

[0130] C NOxSDPFDs_Lim ≤ C NOxTp_Lim / (1 - η SCR_Max × f )

[0131] At this time, the set value of the upstream SDPF reductant pre-control should satisfy the following relationship:

[0132] ANR ≥ ( C NOxEo - C NOxTp_Lim / (1 - η SCR_Max× f )) / C NOxEo

[0133] wherein η SCR_Max calculated by the SCR chemical reaction kinetics model. When SCR is in the DeNOx efficiency sensitive range, f = 0.5;

[0134] The determination of the SCR carrier temperature range is confirmed by comparing the SCR carrier temperature with the subordinate relationship of 4 SCR temperature ranges;

[0135] The SCR carrier temperature is obtained through the SCR carrier temperature prediction model. The establishment method and parameter identification method of the SCR carrier temperature model are similar to the thermodynamic part of the DOC model.

[0136] Please refer to Figure 10 , when the system enters the control state of Class C reductant supply control, since the oxidation degree of NH3 injected at the SDPF inlet will increase with the increase of temperature, it is necessary to minimize the reductant injection amount at the SDPF inlet. Therefore, the control strategy takes the downstream DeNOx efficiency as the primary target to be achieved. Each individual DeNOx system in the dual-injection system usually does not have a large degree of redundant design. At this time, the downstream SCR may not have the volume to completely eliminate the NOx emissions at the engine outlet. Therefore, when entering the NH3 oxidation efficiency sensitive area of the SDPF, the control system will first calculate the maximum conversion ability of the SCR at the current temperature and space velocity through the downstream SCR chemical reaction kinetics model, and then calculate the urea injection amount control target of the 2# nozzle based on the NOx concentration at the engine outlet and the exhaust mass flow rate, and calculate the urea injection amount of the 1# nozzle at the SDPF inlet based on this.

[0137] Please refer to Figure 11 , which shows the structural schematic diagram of the reductant collaborative and efficient distribution system for the dual-stage urea injection system in the second embodiment of the present invention. The system includes:

[0138] [[ID=3l]]A model construction module 10, configured to confirm the catalytic unit composition of the target after-treatment system, and establish corresponding thermodynamic models and chemical reaction kinetics models for the catalytic unit. The thermodynamic models include a convective heat transfer model, a heat conduction model, and a thermal radiation model. The chemical reaction kinetics models include a NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetics model;

[0139] a parameter identification module 20 for completing parameter identification of each of the thermodynamic models and each of the chemical reaction kinetic models through small-sample experiments, wherein the parameters include convective heat transfer coefficient, thermal conductivity, specific heat capacity, thermal radiation / heat transfer coefficient, chemical reaction activation energy, chemical reaction pre-exponential factor, and reaction temperature;

[0140] The temperature zone division module 30 is used to build an engine test bench to conduct a performance test on SCR and SDPF, and divide the carrier temperature of SCR and SDPF into four consecutive temperature intervals according to the test results. The four temperature intervals corresponding to SCR are the DeNO x Invalid zone, SCR DeNO x The efficiency sensitive range, SCR high efficiency conversion range and SCR NH3 oxidation efficiency sensitive range, and the four temperature ranges corresponding to SDPF are SDPF DeNO x Invalid section, DeNO of SDPF x efficiency sensitive range, SDPF passive regeneration efficiency sensitive range, and SDPF NH3 oxidation efficiency sensitive range;

[0141] The injection control module 40 is used to obtain the current carrier temperature of the SCR and SDPF at intervals of a first preset time, and execute a corresponding target reductant distribution strategy based on the current carrier temperature of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy, wherein the first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR.

[0142] Furthermore, the injection control module 40 further includes:

[0143] The first control state execution unit is used to switch to the Class A reducing agent supply control state when the SDPF carrier temperature is monitored to enter the SDPF DeNOx efficiency sensitive area. At this time, the real-time NH3 storage amount signal, SDPF inlet NO2 concentration signal, SDPF carrier temperature signal, SDPF inlet NO x The concentration signal, exhaust mass flow signal and inlet NH3 concentration signal are input, and the established SDPF SCR chemical reaction kinetic model is used to calculate the real-time NH3 storage amount and the real-time DeNO of the SDPF catalyst. x Efficiency, SDPF export NO x concentration, NO2 concentration at SDPF outlet and NH3 concentration at SDPF outlet;

[0144] The first injection demand calculation unit is used to update the real-time NH3 storage amount as a model input and to calculate the real-time DeNO of the SDPF catalyst. x Efficiency calculates the required value of urea injection amount of nozzle No. 1;

[0145] Calculate the target DeNO at the inlet of the SCR catalyst based on the concentration limit of the tail pipe NOx emissions x concentration, and calculate the urea injection quantity requirement value of the first nozzle according to the exhaust gas mass flow rate, the target DeNO at the inlet of the SCR catalyst x concentration, and the DeNO at the inlet of the SDPF x concentration;

[0146] Calculate the urea injection quantity of the first nozzle according to the NO x target conversion quantity of the SDPF catalyst.

[0147] The second injection demand calculation unit is used to combine the NO concentration at the SDPF outlet, the NO2 concentration at the SDPF outlet, and the NH3 concentration at the SDPF outlet with the real-time NH3 storage quantity in the SCR, the SCR carrier temperature, and the exhaust gas mass flow rate as the inputs of the model, and calculate the DeNO x efficiency of the SCR catalyst through the SCR chemical reaction kinetics model, so as to calculate the urea injection quantity requirement value of the second nozzle through the DeNO x efficiency of the SCR catalyst; x

[0148] Calculate the urea injection quantity requirement value of the second nozzle according to the exhaust gas mass flow rate, the target DeNO x efficiency of the SCR catalyst, and the target DeNO at the inlet of the SCR catalyst x concentration;

[0149] Calculate the maximum conversion capacity of the SCR at the current temperature and space velocity through the downstream SCR chemical reaction kinetics model, and calculate the urea injection quantity of the second nozzle based on the NO x concentration at the engine outlet and the exhaust gas mass flow rate.

[0150] The second control state execution unit is used to switch the system to the Class B reductant supply control state when it is monitored that the SDPF carrier temperature enters the passive regeneration efficiency sensitive area of the SDPF;

[0151] The third control state execution unit is used to switch the system to the Class C reductant supply control state when it is monitored that the SDPF carrier temperature enters the NH3 oxidation efficiency sensitive area of the SDPF.

[0152] ​In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0153] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for the synergistic and efficient distribution of a reducing agent for a two-stage urea injection system, characterized in that, The method includes: Confirming the composition of the catalytic unit of the target post-treatment system to establish corresponding thermodynamic models and chemical reaction kinetic models for the catalytic unit. The thermodynamic models include a convective heat transfer model, a heat conduction model, and a thermal radiation model. The chemical reaction kinetic models include a NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetic model; Completing the parameter identification of each of the thermodynamic models and each of the chemical reaction kinetic models through a small-scale test. The parameters include a convective heat transfer coefficient, a thermal conductivity, a specific heat capacity, a thermal radiation / heat transfer coefficient, a chemical reaction activation energy, a chemical reaction pre-exponential factor, and a reaction temperature; An engine test bench was built to conduct a performance test on SCR and SDPF. Based on the test results, the carrier temperatures of SCR and SDPF were divided into four continuous temperature intervals. The four temperature intervals corresponding to SCR are the DeNO x Invalid zone, SCR DeNO x The efficiency sensitive range, SCR high efficiency conversion range and SCR NH3 oxidation efficiency sensitive range, the four temperature ranges corresponding to SDPF are SDPF DeNO x Invalid section, DeNO of SDPF x efficiency sensitive range, SDPF passive regeneration efficiency sensitive range, and SDPF NH3 oxidation efficiency sensitive range; Obtaining the current carrier temperatures of the SCR and SDPF every first preset time, and implementing a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy. The first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR.

2. The method for synergistically and efficiently distributing a reducing agent for a two-stage urea injection system according to claim 1, wherein The step of obtaining the current carrier temperatures of the SCR and SDPF every first preset time, and implementing a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy. The first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR includes: When it is monitored that the temperature of the SDPF carrier enters the DeNOx efficiency sensitive area of the SDPF, switch to the Class A reductant supply control state. At this time, use the real-time NH3 storage amount signal, the SDPF inlet NO2 concentration signal, the SDPF carrier temperature signal, the SDPF inlet NO x concentration signal, the exhaust gas mass flow signal and the inlet NH3 concentration signal as inputs, and use the established SCR chemical reaction kinetics model of the SDPF to calculate the real-time NH3 storage amount, the real-time DeNO x efficiency of the SDPF catalyst, the SDPF outlet NO x concentration, the SDPF outlet NO2 concentration and the SDPF outlet NH3 concentration; The real-time NH3 storage volume therein is used as an update of the model input, and the urea injection volume requirement value of the first nozzle is calculated according to the real-time DeNO x efficiency of the SDPF catalyst; SDPF outlet NO x The concentration of SDPF outlet NO, the concentration of SDPF outlet NO2, the concentration of SDPF outlet NH3, the real-time NH3 storage amount of the SCR, the SCR carrier temperature, and the exhaust gas mass flow rate are used as the inputs of the model together. Through the SCR chemical reaction kinetics model, the DeNO x efficiency of the SCR catalyst is calculated, and the DeNO x efficiency of the SCR catalyst is used to calculate the urea injection amount requirement value of the second nozzle.

3. The method for synergistic and efficient distribution of reducing agent for a two-stage urea injection system according to claim 1, wherein, The step of obtaining the current carrier temperatures of the SCR and SDPF every first preset time, and implementing a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy. The first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR further includes: When it is monitored that the SDPF carrier temperature enters the passive regeneration efficiency sensitive area of the SDPF, the system will switch to a Class B reductant supply control state; Determine the temperature range in which the SCR is located based on the current carrier temperature of the SCR, obtain the corresponding target correction coefficient from a preset data table according to the temperature range in which the SCR is located, and obtain the target DeNO x efficiency of the SCR catalyst by multiplying the target correction coefficient by the maximum DeNO x efficiency; Calculate the target DeNO at the inlet of the SCR catalyst based on the concentration limit of the tailpipe NOx emissions x concentration, and calculate the urea injection quantity demand value of the first nozzle based on the exhaust gas mass flow rate, the target DeNO x concentration at the inlet of the SCR catalyst, and the DeNO x concentration at the inlet of the SDPF; Based on the exhaust gas mass flow rate, the target DeNO of the SCR catalyst, x efficiency, and the target DeNO at the inlet of the SCR catalyst, x the urea injection quantity requirement value of the second nozzle is calculated according to the concentration.

4. The method for synergistically and efficiently distributing a reducing agent for a two-stage urea injection system according to claim 3, wherein If the maximum DeNOx efficiency of the SCR catalyst is ηSCR_Max, then the NO x emission concentration C NOxSDPFDs_Lim satisfies the following relationship: C NOxSDPFDs_Lim ≤ C NOxTp_Lim / （1- η SCR_Max × f ） C NOxTp_Lim is the control limit, and f is the correction factor.

5. The method for synergistically and efficiently distributing a reducing agent for a two-stage urea injection system according to claim 1, wherein The step of obtaining the current carrier temperatures of the SCR and SDPF every first preset time, and implementing a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and SDPF, so as to calculate the target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy. The first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR further includes: When it is monitored that the SDPF carrier temperature enters the NH3 oxidation efficiency sensitive area of the SDPF, the system will switch to a Class C reductant supply control state; Calculate the maximum SCR conversion ability at the current temperature and space velocity through the downstream SCR chemical reaction kinetics model, and calculate the urea injection amount of the second nozzle based on the NO x concentration at the engine outlet and the exhaust gas mass flow rate; Based on the NO target conversion amount of the SDPF catalyst x the urea injection amount of the first nozzle is calculated.

6. A reductant collaborative and efficient distribution system for a two-stage urea injection system, characterized in that, The system includes: A model construction module for confirming the composition of the catalytic unit of the target post-treatment system to establish corresponding thermodynamic models and chemical reaction kinetic models for the catalytic unit. The thermodynamic models include a convective heat transfer model, a heat conduction model, and a thermal radiation model. The chemical reaction kinetic models include a NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetic model; A parameter identification module, configured to complete the parameter identification of each of the thermodynamic models and each of the chemical reaction kinetic models through a pilot test, where the parameters include a convective heat transfer coefficient, a thermal conductivity, a specific heat capacity, a thermal radiation / heat transfer coefficient, a chemical reaction activation energy, a chemical reaction pre-exponential factor, and a reaction temperature; The temperature zone division module is used to build an engine test bench to conduct a performance test on SCR and SDPF. According to the test results, the carrier temperature of SCR and SDPF is divided into four continuous temperature intervals. The four temperature intervals corresponding to SCR are the DeNO x Invalid zone, SCR DeNO x The efficiency sensitive range, SCR high efficiency conversion range and SCR NH3 oxidation efficiency sensitive range, the four temperature ranges corresponding to SDPF are SDPF DeNO x Invalid section, DeNO of SDPF x efficiency sensitive range, SDPF passive regeneration efficiency sensitive range, and SDPF NH3 oxidation efficiency sensitive range; An injection control module, configured to obtain the current carrier temperatures of the SCR and the SDPF every first preset time, and execute corresponding target reductant distribution strategies according to the current carrier temperatures of the SCR and the SDPF, so as to calculate the target injection amounts of a first nozzle and a second nozzle according to the target reductant strategy, where the first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR.

7. The reductant cooperative and efficient distribution system for a dual-stage urea injection system according to claim 6, characterized in that The injection control module further includes: The first control state execution unit is used to switch to the Class A reductant supply control state when it monitors that the SDPF carrier temperature enters the DeNOx efficiency sensitive area of the SDPF. At this time, using the real-time NH3 storage amount signal, SDPF inlet NO2 concentration signal, SDPF carrier temperature signal, SDPF inlet NO x concentration signal, exhaust gas mass flow signal and inlet NH3 concentration signal as inputs, and using the established SCR chemical reaction kinetics model of the SDPF to calculate the real-time NH3 storage amount, real-time DeNO x efficiency of the SDPF catalyst, SDPF outlet NO x concentration, SDPF outlet NO2 concentration and SDPF outlet NH3 concentration; The first injection demand calculation unit is used to update the real-time NH3 storage amount therein as the model input, and calculate the urea injection amount demand value of the first nozzle according to the real-time DeNO x efficiency of the SDPF catalyst; The second injection demand calculation unit is used to combine the NO x concentration at the SDPF outlet, the NO2 concentration at the SDPF outlet, and the NH3 concentration at the SDPF outlet with the real-time NH3 storage amount in the SCR, the SCR carrier temperature, and the exhaust gas mass flow rate as the inputs of the model, and calculate the DeNO x efficiency of the SCR catalyst through the SCR chemical reaction kinetics model, so as to calculate the urea injection amount demand value of the second nozzle through the DeNO x efficiency of the SCR catalyst.

8. The reducing agent cooperative and efficient distribution system for a two-stage urea injection system according to claim 7, wherein The injection control module further includes: A second control state execution unit, configured to switch the system to a Class B reductant supply control state when it is monitored that the SDPF carrier temperature enters the passive regeneration efficiency sensitive area of the SDPF; Judge the temperature range where the SCR is located according to the current carrier temperature of the SCR, obtain the corresponding target correction coefficient from the preset data table according to the temperature range where the SCR is located, and obtain the target DeNO x efficiency of the SCR catalyst by multiplying the target correction coefficient by the maximum DeNO x efficiency; The first injection demand calculation unit is used to calculate the target DeNO at the SCR catalyst inlet according to the concentration limit of the tailpipe NOx emission x concentration, and calculate the urea injection amount demand value of the first nozzle according to the exhaust gas mass flow rate, the target DeNO at the SCR catalyst inlet x concentration, and the DeNO at the SDPF inlet x concentration; The second injection demand calculation unit is used to calculate the urea injection amount demand value of the second nozzle according to the exhaust gas mass flow rate, the target DeNO x efficiency of the SCR catalyst, and the target DeNO x concentration at the inlet of the SCR catalyst.

9. The reductant collaborative and efficient distribution system for a dual-stage urea injection system according to claim 7, characterized in that, The system further includes: Emission concentration calculation module, used to calculate the NO emission concentration at the outlet of SDPF, if the maximum DeNOx efficiency of the SCR catalyst is ηSCR_Max, which satisfies the following relationship: x Emission concentration C NOxSDPFDs_Lim Satisfy the following relationship: C NOxSDPFDs_Lim ≤ C NOxTp_Lim / （1- η SCR_Max × f ） C NOxTp_Lim is the control limit, and f is the correction factor.

10. The reductant collaborative and efficient distribution system for a dual-stage urea injection system according to claim 8, wherein The injection control module further includes: A third control state execution unit, configured to switch the system to a Class C reductant supply control state when it is monitored that the SDPF carrier temperature enters the NH3 oxidation efficiency sensitive area of the SDPF; The second injection demand calculation unit is used to calculate the maximum SCR conversion capacity at the current temperature and airspeed through the downstream SCR chemical reaction kinetics model, and calculate the urea injection amount of the second nozzle based on the NO x concentration at the engine outlet and the exhaust gas mass flow rate; The first injection demand calculation unit is used to calculate the urea injection amount of the first nozzle according to the NO x target conversion amount of the SDPF catalyst.

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