CN116576004B

CN116576004B - Reducing agent cooperative efficient distribution method and system for two-stage urea injection system

Info

Publication number: CN116576004B
Application number: CN202310607448.9A
Authority: CN
Inventors: 王天田; 骆旭薇; 廖善彬; 郭华锋; 熊建; 邹笔锋
Original assignee: Jiangling Motors Corp Ltd
Current assignee: Jiangling Motors Corp Ltd
Priority date: 2023-05-26
Filing date: 2023-05-26
Publication date: 2025-08-01
Anticipated expiration: 2043-05-26
Also published as: CN116576004A

Abstract

This invention proposes a method and system for synergistically efficiently distributing reductant for a two-stage urea injection system. This method, based on the performance of the SDPF and SCR in different temperature ranges, determines a temperature-zone control strategy that is more conducive to balancing the passive regeneration efficiency of PM on the SDPF, the overall DeNOx efficiency of the two-stage SCR system, and the reductant energy efficiency ratio. This control strategy, based on accurate modeling of the thermodynamic processes and chemical reaction kinetics of the after-treatment system, adopts a targeted reductant distribution strategy based on the operating characteristics of the after-treatment system at different temperatures to maximize the comprehensive performance of the after-treatment components. This invention effectively improves the passive regeneration performance and urea energy efficiency ratio of the after-treatment system without affecting its DeNOx efficiency.

Description

Reducing agent cooperative efficient distribution method and system for two-stage urea injection system

Technical Field

The invention relates to the technical field of reducing agent utilization of a diesel engine aftertreatment system, in particular to a reducing agent synergistic efficient distribution method and system for a two-stage urea injection system.

Background

The exhaust gas of the diesel engine contains more nitrogen oxides (NO _x) and Particulate Matters (PM), the existing emission regulations limit the emission amount of NO _x and PM, limit values of different degrees are regulated, and as the emission regulations are further tightened, the weighting factors of the corresponding emission limit values on the emission of the cold start working condition are obviously increased, so that the development of the aftertreatment system to the size and function tight coupling direction is promoted.

NO _x is a reaction product of N ₂ and O ₂ in air in a cylinder inhaled by an engine at high temperature, and its main components are NO and NO ₂. Urea selective catalytic reduction technology (Urea-SCR technology for short) is a main technology for controlling NO _x emission of an engine, and the most common form of the technology is that ammonia (NH ₃) is generated by decomposing Urea aqueous solution, and under the action of an SCR catalyst, the ammonia and NO _x undergo selective catalytic reduction reaction to generate nitrogen and water, and then the nitrogen and water are discharged into the atmosphere, and the emission amount of NO _x is effectively controlled by spraying different Urea amounts into the exhaust gas of a diesel engine. Hydrolysis and pyrolysis reactions of urea do not take place sufficiently at temperatures below 187 ℃, while the reaction rate of SCR reactions at temperatures below 250 ℃ is significantly affected by the ratio of NO ₂/NO_x, the real-time ammonia storage, the temperature and the space velocity.

PM is a reaction product of injected fuel oil, engine oil and the like under high temperature and partial oxygen deficiency conditions in a cylinder, and mainly comprises soot, soluble organic matters and sulfate. The current primary means of particulate matter control is the use of diesel particulate traps (DPFs), which trap most of the PM inside the carrier through a wall flow structure, preventing it from entering the atmosphere. PM is continuously accumulated in the DPF during use, which causes an exhaust back pressure to gradually rise to affect the normal operation of the engine, so that PM accumulated in the DPF is periodically eliminated through a high-temperature oxidation reaction, which is called an active regeneration process. Active regeneration typically requires additional fuel consumption to raise the exhaust temperature to bring the PM to an oxidized condition, thus resulting in increased fuel consumption.

As the aftertreatment system evolves toward a tight coupling direction in terms of size and function, the technology of coating SCR catalyst (SDPF) on the surface of DPF begins to emerge, which completes 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.

To cope with the stricter requirements of future emission regulations on emissions in the cold start stage, a two-stage scr+urea injection system is usually adopted, and the front stage is as close to the engine outlet as possible to reach the high-efficiency reaction temperature more quickly. There are many technical routes for the two-stage scr+urea injection system, such as oxidation catalyst (DOC) +sdpf+scr+ammonia oxidation catalyst (ASC), doc+scr+asc+dpf+scr+asc, and so on. The space and cost of arrangement of the technical routes comprising the SDPF system are obviously advantageous, and therefore, the application is wider.

The following problems are also present with the use of SDPF. SDPF achieves selective catalytic conversion capability for NO _x by coating the SCR catalyst on the entire support surface, but the oxidation catalytic reaction is not selective and directly oxidizes NH ₃, so SDPF coated with SCR catalyst is not typically further coated with oxidation catalyst. Because the SCR reaction preferentially consumes NO ₂ in the exhaust gas, the passive regeneration capability of the SDPF is seriously weakened, the active regeneration interval is shortened, and the oil consumption and the service life of an aftertreatment system are influenced. The urea distribution strategy of the conventional two-stage injection system of SDPF+SCR is usually based on upstream SDPF, and downstream SCR is used as a supplement for the insufficient reaction capacity of upstream SDPF, at this time, a large amount of reducing agent reacts on SDPF, NO ₂ almost does not remain, and the after-treatment system under the application of the strategy has the condition of short regeneration interval. In addition, the traditional distribution strategy of the two-stage urea distribution system is characterized in that the urea injection quantity is concentrated at an SDPF inlet with higher temperature under the high-temperature working condition, so that the injected urea is oxidized to a greater extent, and the energy efficiency of the reducing agent is poor.

The reduction agent of the two-stage injection system provided by the invention is matched with an efficient distribution strategy, and meanwhile, the passive regeneration of PM on the SDPF and the overall DeNOx efficiency of the two-stage SCR system are simultaneously considered, so that the reduction agent is beneficial to helping the engine-aftertreatment system to achieve lower emission and oil consumption targets.

Disclosure of Invention

Based on the above, the invention aims to provide a reducing agent cooperative high-efficiency distribution method and a reducing agent cooperative high-efficiency distribution system for a two-stage urea injection system, which can effectively improve the passive regeneration performance and the urea energy efficiency ratio of an aftertreatment system under the condition of not influencing the DeNOx efficiency of the aftertreatment system.

In one aspect, the invention provides a method for synergistic and efficient distribution of a reducing agent for a two-stage urea injection system, the method comprising:

Confirming the catalytic unit constitution of a target aftertreatment system to establish a corresponding thermodynamic model and a chemical reaction kinetic model aiming at the catalytic unit, wherein the thermodynamic model comprises a convection heat transfer model, a heat conduction model and a heat radiation model, and the chemical reaction kinetic model comprises an NO oxidation reaction model, a CRT reaction model and an SCR chemical reaction kinetic model;

Completing parameter identification of each thermodynamic model and each chemical reaction kinetic model through a sample test, wherein the parameters comprise a convective heat transfer coefficient, a heat conduction coefficient, a specific heat capacity, a heat radiation/heat transfer coefficient, chemical reaction activation energy, a chemical reaction pre-factor and a reaction temperature;

Setting up an engine test bed to perform a performance bottoming test on the SCR and the SDPF, and dividing the carrier temperatures of the SCR and the SDPF into four continuous temperature intervals according to the bottoming test result, wherein the four temperature intervals corresponding to the SCR are a DeNO _x invalid interval of the SCR, a DeNO _x efficiency sensitive interval of the SCR, a high-efficiency conversion interval of the SCR and a NH ₃ oxidation efficiency sensitive interval of the SCR in sequence, and the four temperature intervals corresponding to the SDPF are a DeNO _x invalid interval of the SDPF, a DeNO _x efficiency sensitive interval of the SDPF, a passive regeneration efficiency sensitive interval of the SDPF and a NH ₃ oxidation efficiency sensitive interval of the SDPF in sequence;

And acquiring the current carrier temperatures of the SCR and the SDPF at intervals of a first preset time, and executing a corresponding target reducing agent distribution strategy according to the current carrier temperatures of the SCR and the SDPF so as to calculate and obtain target injection amounts of a first nozzle and a second nozzle according to the target reducing agent strategy, wherein the first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR.

In summary, according to the reducing agent cooperative high-efficiency distribution method for the two-stage urea injection system, a temperature partition control strategy which is more beneficial to considering the passive regeneration efficiency of PM on SDPF, the overall DeNOx efficiency of the two-stage SCR system and the energy efficiency ratio of the reducing agent is determined based on the performance of SDPF and SCR in different temperature intervals through the reducing agent cooperative high-efficiency distribution strategy, and the control strategy is established on the basis of accurately modeling the thermodynamic process and the chemical reaction kinetics engineering of the aftertreatment system, and fully exerts the comprehensive performance of the aftertreatment component aiming at the working characteristics of the aftertreatment system at different temperatures by adopting the high-efficiency reducing agent distribution strategy. Helping to achieve lower emissions and energy consumption goals for engine-aftertreatment systems.

In a preferred embodiment of the present invention, the current carrier temperatures of the SCR and the SDPF are obtained at intervals of a first preset time, and a corresponding target reductant distribution strategy is executed according to the current carrier temperatures of the SCR and the SDPF, so as to calculate a target injection amount 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, and the steps of:

When the temperature of the SDPF carrier is monitored to enter a DeNOx efficiency sensitive region of the SDPF, switching to a class A reducing agent supply control state, wherein a real-time NH ₃ storage quantity, a real-time DeNO _x efficiency of the SDPF catalyst, a concentration of an SDPF outlet NO _x, a concentration of an SDPF outlet NO ₂ and a concentration of an SDPF outlet NH ₃ are calculated by using the established SCR chemical reaction kinetic model of the SDPF and taking a real-time NH ₃ quantity signal, a concentration signal of the SDPF inlet NO ₂, a SDPF carrier temperature signal, a concentration signal of the SDPF inlet NO _x, an exhaust mass flow signal and a concentration signal of the inlet NH ₃ as inputs;

the real-time NH ₃ quantity is used as the update of the model input, and the urea injection quantity requirement value of the first nozzle is calculated according to the real-time DeNO _x efficiency of the SDPF catalyst;

The concentration of NO _x at the outlet of the SDPF, the concentration of NO ₂ at the outlet of the SDPF and the concentration of NH ₃ at the outlet of the SDPF are used as the input of a model in combination with the temperature of the SCR carrier storing the NH ₃ amount in real time and the exhaust mass flow, the DeNO _x efficiency of the SCR catalyst is calculated through the SCR chemical reaction kinetic model, and the urea injection quantity required value of the No. two nozzle is calculated through the DeNO _x efficiency of the SCR catalyst.

In a preferred embodiment of the present invention, the current carrier temperatures of the SCR and the SDPF are obtained at intervals of a first preset time, and a corresponding target reductant distribution strategy is executed according to the current carrier temperatures of the SCR and the SDPF, so as to calculate a target injection quantity 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, and the steps further include:

When the SDPF carrier temperature is monitored to enter a passive regeneration efficiency sensitive zone of the SDPF, the system will switch to a class B reductant supply control state;

Judging a temperature interval in which the SCR is positioned according to the current carrier temperature of the SCR, acquiring a corresponding target correction coefficient from a preset data table according to the temperature interval in which the SCR is positioned, and obtaining target DeNO _x efficiency of the SCR catalyst according to the product of the target correction coefficient and the maximum DeNO _x efficiency of the SCR catalyst;

Calculating a target DeNO _x concentration of an SCR catalyst inlet according to a concentration limit value of tail pipe NOx emission, and calculating a urea injection quantity required value of a first nozzle according to the exhaust mass flow, a target DeNO _x concentration of the SCR catalyst inlet and a DeNO _x concentration of an SDPF inlet;

The urea injection demand for nozzle number two is calculated based on the exhaust mass flow, the target DeNO _x efficiency of the SCR catalyst, and the target DeNO _x concentration at the SCR catalyst inlet.

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} at the SDPF outlet satisfies the following relationship:

C_{NOxSDPFDs_Lim}≤C_{NOxTp_Lim}/（1-η_{SCR_Max}×f)

C _{NOxTp_Lim} is a control limit value, and f is a correction coefficient.

When the temperature of the SDPF carrier is monitored to enter the NH3 oxidation efficiency sensitive zone of the SDPF, the system will switch to a class C reductant supply control state;

Calculating the SCR maximum conversion capacity under the current temperature and airspeed through a downstream SCR chemical reaction kinetic model, and calculating the urea injection quantity of a No. two nozzle based on the concentration of NO _x at an engine outlet and an exhaust mass flow meter;

the urea injection from nozzle number one is calculated based on the target NO _x conversion of the SDPF catalyst.

In another aspect, the present invention also provides a reductant co-efficient dispensing system for a dual stage urea injection system, the system comprising:

The model construction module is used for confirming the catalytic unit constitution of the target aftertreatment system so as to establish a corresponding thermodynamic model and a chemical reaction kinetic model aiming at the catalytic unit, wherein the thermodynamic model comprises a convection heat transfer model, a heat conduction model and a heat radiation model, and the chemical reaction kinetic model comprises an NO oxidation reaction model, a CRT reaction model and an SCR chemical reaction kinetic model;

The parameter identification module is used for completing parameter identification of each thermodynamic model and each chemical reaction kinetic model through a sample test, wherein the parameters comprise a convection heat transfer coefficient, a heat conduction coefficient, a specific heat capacity, a heat radiation/heat transfer coefficient, chemical reaction activation energy, a chemical reaction pre-factor and a reaction temperature;

The temperature zone dividing module is used for building an engine test bed to perform a performance bottoming test on the SCR and the SDPF, dividing the carrier temperatures of the SCR and the SDPF into four continuous temperature zones according to a bottoming test result, wherein the four temperature zones corresponding to the SCR are a DeNO _x invalid zone of the SCR, a DeNO _x efficiency sensitive zone of the SCR, a high-efficiency conversion zone of the SCR and a NH ₃ oxidation efficiency sensitive zone of the SCR in sequence, and the four temperature zones corresponding to the SDPF are a DeNO _x invalid zone of the SDPF, a DeNO _x efficiency sensitive zone of the SDPF, a passive regeneration efficiency sensitive zone of the SDPF and a NH ₃ oxidation efficiency sensitive zone of the SDPF in sequence;

The injection control module is used for acquiring the current carrier temperatures of the SCR and the SDPF at intervals of a first preset time, executing a corresponding target reducing agent distribution strategy according to the current carrier temperatures of the SCR and the SDPF, and calculating to obtain target injection amounts of a first nozzle and a second nozzle according to the target reducing agent strategy, wherein the first nozzle corresponds to the SDPF, and the second nozzle corresponds to the SCR.

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

A first control state execution unit for switching to a class a reductant supply control state when the monitored SDPF carrier temperature enters a DeNOx efficiency sensitive zone of the SDPF, where the real-time stored NH ₃ amount, the real-time DeNO _x efficiency of the SDPF catalyst, the SDPF outlet NO _x concentration, the SDPF outlet NO ₂ concentration, and the SDPF outlet NH ₃ concentration are calculated using the established SCR chemical reaction kinetics model of the SDPF, with the real-time stored NH ₃ amount signal, the SDPF inlet NO ₂ concentration signal, the SDPF carrier temperature signal, the SDPF inlet NO _x concentration signal, the exhaust mass flow signal, and the inlet NH ₃ concentration signal as inputs;

The first injection demand amount calculation unit is used for updating the real-time NH ₃ amount stored in the first injection demand amount calculation unit as a model input and calculating the urea injection demand value of the first nozzle according to the real-time DeNO _x efficiency of the SDPF catalyst;

And the second injection demand amount calculation unit is used for taking the concentration of the NO _x at the outlet of the SDPF, the concentration of the NO ₂ at the outlet of the SDPF and the concentration of the NH ₃ at the outlet of the SDPF as the input of a model together with the temperature of the SCR carrier storing the NH ₃ amount in real time and the exhaust gas mass flow rate, calculating DeNO _x efficiency of the SCR catalyst through the SCR chemical reaction kinetic model, and calculating the urea injection demand value of the No. two nozzles through DeNO _x efficiency of the SCR catalyst.

A second control state execution unit for switching the system to a class B reductant supply control state when the SDPF carrier temperature is monitored to enter a passive regeneration efficiency sensitive zone of the SDPF;

A first injection demand amount calculation unit for calculating a target DeNO _x concentration of the SCR catalyst inlet according to a concentration limit value of tailpipe NOx emission, and calculating a urea injection demand value of the first nozzle according to an exhaust mass flow rate, a target DeNO _x concentration of the SCR catalyst inlet, and a DeNO _x concentration of the SDPF inlet;

And the second injection demand amount calculation unit is used for calculating the urea injection demand value of the second nozzle according to the exhaust gas mass flow, the target DeNO _x efficiency of the SCR catalyst and the target DeNO _x concentration of the SCR catalyst inlet.

In a preferred embodiment of the present invention, the system further comprises:

the emission concentration calculation module is configured to, if the maximum DeNOx efficiency of the SCR catalyst is ηscr_max, make the NO _x emission concentration C _{NOxSDPFDs_Lim} at the SDPF outlet satisfy the following relationship:

C_{NOxSDPFDs_Lim}≤C_{NOxTp_Lim}/（1-η_{SCR_Max}×f)

C _{NOxTp_Lim} is control limit, f is correction coefficient

a third control state execution unit for switching the system to a class C reductant supply control state when the SDPF carrier temperature is monitored to enter the NH3 oxidation efficiency sensitive zone of the SDPF;

The second injection demand calculation unit is used for calculating the SCR maximum conversion capacity under the current temperature and the airspeed through a downstream SCR chemical reaction kinetic model and calculating the urea injection quantity of the second nozzle based on the concentration of NO _x at an engine outlet and an exhaust mass flow meter;

and the first injection demand amount calculation unit is used for calculating the urea injection amount of the first nozzle according to the NO _x target conversion amount of the SDPF catalyst.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

FIG. 1 is a flow chart of a reductant co-efficient dispensing method for a dual stage urea injection system in accordance with a first embodiment of the present invention;

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

FIG. 3 is a flow chart illustrating implementation of a reductant co-efficient dispensing strategy for a dual stage urea injection system;

FIG. 4 is a schematic diagram of SDPF temperature interval partitioning;

FIG. 5 is a schematic diagram of SCR temperature interval division;

FIG. 6 is a prediction flow chart for DOC outlet NO ₂ ratio prediction;

FIG. 7 is a diagram of reductant supply control states with SDPF carrier temperature at different temperature intervals;

FIG. 8 is a schematic diagram of a urea injection control strategy in a class A reductant supply control state;

FIG. 9 is a urea injection control strategy with a class B reductant supply control state;

FIG. 10 is a schematic diagram of a urea injection control strategy in the class C reductant supply control state;

FIG. 11 is a schematic diagram of a reductant co-efficient dispensing system for a dual stage urea injection system in accordance with a second embodiment of the present invention.

The invention will be further described in the following detailed description in conjunction with the above-described figures.

Detailed Description

In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Several embodiments of the invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

Referring to fig. 3, the method for synergistic and efficient distribution of reducing agent for a two-stage urea injection system according to the present invention mainly comprises the following steps:

And (1) establishing a carrier temperature estimation model of the DOC, the SDPF and the SCR, and realizing the carrier temperature estimation of the DOC, the SDPF and the SCR. The carrier temperature pre-estimation model of the SDPF and the SCR mainly models thermodynamic processes of 1) heat convection between exhaust and a catalyst, 2) heat conduction inside the catalyst, 3) radiation heat exchange of a catalyst shell to atmosphere, and establishes a corresponding HC oxidation heat release correction model by taking further oxidation heat release of HC on the DOC into consideration except thermodynamic parts.

And (2) establishing a DOC NO oxidation reaction kinetic model to realize the NO ₂ proportion prediction of the DOC outlet.

Step (3), establishing an SCR chemical reaction kinetic model of the SDPF and the SCR catalyst, and respectively calculating DeNOx reaction processes occurring on the SDPF and the SCR;

Step (4) divides the DeNOx invalid zone of the SDPF, the DeNOx efficiency sensitive zone of the SDPF, the passive regeneration efficiency sensitive zone of the SDPF and the NH ₃ oxidation efficiency sensitive zone of the SDPF into 4 continuous temperature zones based on the carrier temperature of the SDPF through a performance bottoming test of the SDPF.

And (5) dividing 4 continuous temperature intervals among a DeNOx invalid zone of the SCR, a DeNOx efficiency sensitive zone of the SCR, a high-efficiency conversion zone of the SCR and an NH ₃ oxidation efficiency sensitive zone of the SCR based on the carrier temperature of the SCR through a performance bottoming test of the SCR.

Step (6) will monitor the carrier temperatures of the SDPF and SCR in real time and take this as an input to adjust the control objective of the reductant dispensing strategy. The reductant supply control system will not supply reductant when the monitored SDPF carrier temperature is in the DeNOx inactive region of the SDPF, will switch to the class A reductant supply control state when the monitored SDPF carrier temperature enters the DeNOx efficiency sensitive region of the SDPF, will switch to the class B reductant supply control state when the monitored SDPF carrier temperature enters the passive regeneration efficiency sensitive region of the SDPF, and will switch to the class C reductant supply control state when the monitored SDPF carrier temperature enters the NH ₃ oxidation efficiency sensitive region of the SDPF

Step (7), when the system is monitored to enter the A-type reducing agent supply control state control, the upstream reducing agent supply rate is distributed by taking the DeNOx efficiency on the SDPF as a main control target, and if the DeNOx efficiency of the SDPF is insufficient, the downstream SCR is supplemented;

And (8) when the system is monitored to enter the control state of the B-type reducing agent supply, switching the basic control target to the condition that the tail pipe NOx emission does not exceed the limit value, and improving the passive regeneration efficiency of the SDPF as much as possible. When the temperature of the SCR carrier is in different temperature partitions, different DeNOx capacity correction coefficients are adopted to control the downstream DeNOx ratio so as to avoid the condition that the downstream SCR cannot completely convert NOx at the outlet of the SDPF and the emission exceeds the regulation limit;

When step (9) is performed after monitoring that the system is in the control state of the C-type reducing agent supply, the control strategy is aimed at the downstream DeNOx efficiency, since the oxidation degree of NH ₃ injected at the inlet of the SDPF increases with the temperature, and the reducing agent injection amount at the inlet of the SDPF needs to be reduced as much as possible. Each individual DeNOx system in a dual injection system typically does not have a largely redundant design, where the downstream SCR may not have a volume to completely eliminate engine outlet NOx emissions, so when entering the NH ₃ oxidation efficiency sensitive zone of the SDPF, the control system operates logic to first calculate the SCR maximum conversion capability at the current temperature and space velocity from the downstream SCR chemical reaction kinetics model, and then calculate the reductant supply to the inlet of the SDPF based thereon;

In summary, the method provided by the invention comprises the steps of firstly confirming the catalytic unit constitution of a target aftertreatment system, then establishing a corresponding thermodynamic model and a chemical reaction kinetic model for the target catalytic unit, completing parameter identification of the thermodynamic model and the chemical reaction kinetic model through a small sample test, completing temperature interval division of a 1# catalyst and a 2# catalyst through a performance test result carried out by an engine test bench, monitoring the SDPF carrier temperature in real time, if the SDPF carrier temperature is in a DeNOx ineffective interval, NO reducing agent supply is needed at this time, if the SDPF carrier temperature is in a DeNOx efficiency sensitive interval, adopting a class A reducing agent supply control strategy taking DeNOx capacity of a 1# catalyst as a main control target at this time, if the SDPF carrier temperature is in a passive regeneration efficiency sensitive interval, adopting a class B reducing agent supply control strategy at this time, improving the passive regeneration efficiency of a DPF as much as possible under the condition that the tail pipe NO _x emission does not exceed a limit value, and determining different DeNOx capacity correction coefficients based on the temperature interval of the 2# catalyst under the condition of the class B reducing agent supply control state so as to complete calculation of 2 nozzle target amounts, and if the SDPF carrier temperature is in a DeNOx efficiency sensitive interval, and if the temperature is in a DeNOx carrier temperature is ₃, adopting a full control strategy to realize the reduction of the class C catalyst as a main control target.

The invention has the beneficial effects that the passive regeneration performance and the reducing agent energy efficiency ratio are effectively improved under the condition of not influencing the DeNOx efficiency of the aftertreatment system.

It should be further noted that the surface of the SDPF carrier is typically coated with only the SCR catalyst, and the SCR reaction preferentially consumes NO ₂ in the exhaust gas, which severely weakens the passive regeneration capability of the SDPF, shortens the active regeneration interval, and affects fuel consumption and the service life of the aftertreatment system. The urea distribution strategy of the conventional two-stage injection system of SDPF+SCR is usually based on upstream SDPF, and downstream SCR is used as a supplement for the insufficient reaction capacity of upstream SDPF, at this time, a large amount of reducing agent reacts on the SDPF, NO ₂ almost does not remain, the passive regeneration performance of the SDPF is greatly affected, and the after-treatment system applying the strategy has short regeneration interval. In addition, the traditional distribution strategy of the two-stage urea distribution system is characterized in that the injected urea is oxidized to a greater extent and the energy efficiency of the reducing agent is poor under the high-temperature working condition because the urea injection quantity is concentrated at the inlet of the SDPF with higher temperature.

The reducing agent collaborative efficient distribution strategy provided by the invention is based on the performance of SDPF and SCR in different temperature intervals, and a temperature partition control strategy which is more favorable for considering the passive regeneration efficiency of PM on the SDPF, the overall DeNOx efficiency of a two-stage SCR system and the energy efficiency ratio of the reducing agent is determined, wherein the control strategy is established on the basis of accurately modeling the thermodynamic process and the chemical reaction dynamics engineering of the aftertreatment system, and the comprehensive performance of the aftertreatment component is fully exerted by adopting the efficient reducing agent distribution strategy aiming at the working characteristics of the aftertreatment system at different temperatures. Helping to achieve lower emissions and energy consumption goals for engine-aftertreatment systems.

Referring to fig. 2, the aftertreatment system corresponding to the preferred embodiment of the present invention is a doc+sdpf+scr+asc scheme, matching a dual-stage urea injection system. The exhaust gas passes through the oxidation catalysis of the DOC to oxidize HC, CO and other reducing gases are oxidized, NO can be further reacted with O ₂ on the DOC to generate NO ₂, after the temperature of the SDPF carrier exceeds the starting and spraying critical temperature of urea, a No. 1 urea nozzle (No. 1 nozzle) starts to spray urea, the sprayed urea is subjected to pyrolysis and hydrolysis reaction under the heating effect of exhaust gas to generate NH ₃,NH₃, the NH ₃,NH₃ reacts with the NOx rapidly under the effect of an SCR catalyst coated on the SDPF to generate N ₂ and H ₂ O, if the urea spraying amount is insufficient, the rest NOx can continue to flow downstream, if the urea spraying amount is excessive, the rest NH ₃ can flow downstream, the downstream SCR serves as a redundant DeNOx system to carry out the rest NOx conversion operation, the No. 2 urea nozzle (No. two nozzle) supplies the needed reducing agent to the downstream SCR system, the arrangement position of the SCR system can be far away from the SDPF to obtain larger temperature difference, and in the arrangement mode, if the temperature of the upstream SDPF is too high, the conversion efficiency is reduced, the downstream SCR can still realize excellent overall conversion efficiency of the system by virtue of the temperature difference. The reductant supply system of the entire aftertreatment system uses an aqueous urea solution with a mass concentration of 32.5% as reductant. The ECU and the DCU can be mutually independent hardware structures or can be combined into a complete control unit, and the ECU and the DCU collect the engine speed, the engine fuel injection quantity, the air inlet temperature, the air inlet pressure, the air inlet mass flow, the EGR valve opening, the cooling water temperature, a DOC catalyst upstream temperature sensor, an SDPF catalyst upstream temperature sensor, an SCR catalyst downstream temperature sensor, a DOC catalyst upstream NO _x concentration sensor, The signals sent by the NO _x concentration sensor at the upstream of the SCR catalyst, the NO _x concentration sensor at the downstream of the SCR catalyst, the urea liquid level sensor and the like are calculated through corresponding control function modules to complete the synergistic efficient distribution of the reducing agent of the two-stage injection system, so that the aims of simultaneously optimizing the passive regeneration performance of PM on the SDPF and improving the overall DeNOx efficiency of the two-stage SCR system are fulfilled.

Referring to fig. 1, a flowchart of a method for synergistic efficient distribution of reductant for a dual-stage urea injection system according to a first embodiment of the present invention is shown, the method comprising steps S01 to S04, wherein:

step S01, confirming the catalytic unit constitution of a target aftertreatment system so as to establish a corresponding thermodynamic model and a chemical reaction kinetic model aiming at the catalytic unit;

Wherein the thermodynamic model comprises a convective heat transfer model, a thermal conduction model and a thermal radiation model, and the chemical reaction kinetics model comprises an NO oxidation reaction model, a CRT reaction model and an SCR chemical reaction kinetics model.

Specifically, referring to fig. 6, first, the relationship between the engine outlet NO ₂/NOx ratio and the engine fuel injection amount, the rotation speed, and the EGR rate is experimentally determined and the engine outlet NO ₂/NOx ratio MAP is obtained. When the system works, the basic engine outlet NO ₂/NOx ratio can be obtained by checking the engine outlet NO ₂/NOx ratio MAP through the engine fuel injection quantity, the rotating speed and the EGR rate, and then the more accurate engine outlet NO ₂/NOx ratio is obtained as one of the input of the NO oxidation reaction kinetic model of the DOC through the correction of the cooling water temperature, the air inlet temperature and the air inlet pressure;

and secondly, establishing a DOC carrier temperature prediction model comprising an HC oxidation heat release model and a thermodynamic process model. The DOC support temperature obtained by this model will be one of the inputs to the DOC's NO oxidation reaction kinetics model.

Under the condition that the DOC catalytic performance is determined, the inlet temperature and the exhaust gas mass flow rate determine the occurrence degree of HC oxidation reaction, and the post-injection oil quantity determines the total heat which can be released when the HC oxidation reaction completely occurs, so that the HC oxidation heat release correction model established by the invention takes the post-injection oil quantity of the engine, the engine speed, the exhaust gas mass flow rate and the 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 an energy source of exhaust gas to be input into a thermodynamic process model to finish accurate estimation of the DOC carrier temperature;

The post-engine fuel injection quantity, the engine rotating speed and the DOC inlet temperature are respectively obtained through calculation of a fuel injection pulse width signal, a rotating speed sensor signal and an exhaust temperature sensor signal of the DOC inlet by an Engine Control Unit (ECU), and the exhaust mass flow is obtained through calculation of an air inlet mass flow sensor signal and a fuel injection quantity signal of the ECU;

The thermodynamic process model of DOC mainly models the thermodynamic process of 1) convective heat transfer between exhaust gas and catalyst, 2) heat transfer inside the catalyst, 3) radiative heat transfer of the catalyst shell to the atmosphere, and the model description method is as follows:

1) Convection heat exchange amount between exhaust gas and catalyst in unit time Can be calculated by

Wherein h is the heat exchange coefficient of the convection heat exchange of 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 surface area of the catalyst which can be contacted with the exhaust gasRepresents the porosity of the catalyst (i.e., the ratio of the circulated exhaust gas volume per unit of the nominal catalyst volume,%), S _cat represents the catalyst internal surface area per unit of the circulated gas volume of the catalyst, m ²/m³. Wherein a _H-T can be represented as:

wherein: L _C is the length of the catalyst, m; I.e., the total volume of the catalyst V _C; i.e., the total cross-sectional area of the catalyst, a _f; Indicating the area where exhaust gas is blocked by the catalyst. The area of exhaust gas blocked by the catalyst is small and therefore negligible, so the above formula can be expressed as

2) The heat conduction inside the catalyst can be deduced from the fourier theorem, and the heat of the catalyst through the heat conduction per unit time is:

3) The radiative heat transfer of the catalyst housing to the atmosphere can be calculated according to Stefan-Boltzmann's law:

Wherein: The radiation area of the catalyst and the outside is m ²; is the radiation blackness; W/m ²K⁴;T_amb is the ambient temperature, K;

After the carrier temperature pre-estimation model is established, parameter identification is required to be completed through a catalyst sample test. Wherein the thermodynamic parameter identification is realized mainly by carrying out a step-by-step temperature rise test. The standard tail gas with the temperature of 200 ℃, 250 ℃,300 ℃, 350 ℃, 400 ℃, 500 ℃ and 600 ℃ is sequentially introduced, the exhaust temperature is unchanged before each time of reaching the heat balance, meanwhile, the change relation curve of the catalyst carrier temperature along with time at different positions, the carrier radiation heat release rate and the like are recorded, and thermodynamic parameters to be confirmed are the effective circulation volume V of the carrier, the effective cross section area A _fr of the carrier, the convective heat transfer coefficient h, the heat conductivity coefficient lambda, the effective heat transfer area A _{H-T_}, the heat radiation area A _Rad and the specific heat capacity of the carrier 。

And finally, establishing a dynamic model of the NO oxidation reaction of the DOC. The model takes DOC inlet NO _x concentration, inlet O ₂ concentration, inlet NO ₂/NOx ratio, DOC carrier temperature and exhaust mass flow as inputs to calculate the NO oxidation reaction rate occurring on the DOC. The DOC inlet NO _x concentration is obtained through a NOx sensor signal or an engine NOx emission model which is arranged at the DOC inlet, the DOC inlet O ₂ concentration is obtained through an engine combustion model or an oxygen sensor or a NOx sensor at the DOC inlet, the DOC inlet NO ₂/NOx ratio is obtained through table look-up of engine fuel injection quantity, rotating speed and EGR rate, and correction of cooling water temperature, air inlet temperature and air inlet pressure is added, and the DOC carrier temperature is obtained through output results of a DOC carrier temperature prediction model.

The DOC NO oxidation reaction kinetic model only considers the reaction process of NO oxidation under the aerobic condition, the chemical reaction equation of NO oxidation reaction is 2NO+O ₂ßà2NO₂, and the corresponding reaction rate description equation is as follows:

The DOC NO oxidation reaction kinetic model outputs an outlet NO ₂/NO_x signal, an outlet O ₂ concentration signal and an outlet NO ₂ concentration signal in real time, so that the prediction of the NO ₂ concentration and the NO ₂/NO_x proportion of the DOC part is completed.

Step S02, completing parameter identification of each thermodynamic model and each chemical reaction kinetic model through a small sample test;

The parameters comprise a convection heat transfer coefficient, a heat conduction coefficient, a specific heat capacity, a heat radiation/heat transfer coefficient, chemical reaction activation energy, a chemical reaction pre-factor and a reaction temperature;

Step S03, setting up an engine test bench to perform a performance bottoming test on the SCR and the SDPF, and dividing the carrier temperatures of the SCR and the SDPF into four continuous temperature intervals according to the bottoming test result;

the four temperature intervals corresponding to the SCR are a DeNO _x invalid interval of the SCR, a DeNO _x efficiency sensitive interval of the SCR, a high-efficiency conversion interval of the SCR and an NH ₃ oxidation efficiency sensitive interval of the SCR in sequence, and the four temperature intervals corresponding to the SDPF are a DeNO _x invalid interval of the SDPF, a DeNO _x efficiency sensitive interval of the SDPF, a passive regeneration efficiency sensitive interval of the SDPF and an NH ₃ oxidation efficiency sensitive interval of the SDPF in sequence;

Specifically, referring to FIG. 4, the operating state of the SDPF is divided into 4 temperature zones according to the carrier temperature, namely, a DeNOx invalid zone of the SDPF, a DeNOx efficiency sensitive zone of the SDPF, a passive regeneration efficiency sensitive zone of the SDPF and an NH ₃ oxidation efficiency sensitive zone of the SDPF, according to the operating characteristics of the SDPF system.

Wherein, the DeNOx ineffective zone of SDPF is determined by the lowest temperature at which hydrolysis and pyrolysis reactions of urea can occur, so the temperature range is (-273 ℃ and 185 ℃);

The DeNOx efficiency sensitive temperature interval of the SDPF was obtained by conducting DeNOx efficiency tests of the SDPF under different conditions of temperature, space velocity, ammonia storage amount and NO ₂/NO_x ratio. When the SDPF carrier temperature is higher than 250 ℃, the DeNOx efficiency on the SDPF is NO longer increased with the increase of temperature, and the airspeed, ammonia storage amount and NO ₂/NO_x ratio NO longer have an effect on the DeNOx efficiency, thus the temperature range of the DeNOx efficiency sensitive temperature interval is set to [185 ℃,250 ℃);

The temperature interval sensitive to the passive regeneration efficiency of the SDPF is obtained by the passive regeneration rate test of the SDPF under different temperatures, airspeeds, carbon loads and NO ₂/NO_x ratios. When the SDPF carrier temperature exceeds 250 ℃, the reaction of NO ₂ and PM starts to occur, when the temperature exceeds 350 ℃, the reaction rate of O ₂ and PM is equivalent to the reaction rate of NO ₂ and PM, and the passive regeneration reaction rate after the temperature is influenced by the concentration of NO ₂ is lower, so that the temperature range of the sensitive temperature interval of the passive regeneration efficiency is defined as [250 ℃ and 350 ℃;

The NH ₃ oxidation efficiency sensitive temperature interval of the SDPF is obtained by carrying out DeNOx efficiency tests of the SDPF under different temperature and space velocity conditions. When the temperature of the SDPF carrier is higher than 350 ℃, NH ₃ oxidation phenomenon on the SDPF starts to appear, and as the temperature increases, the degree of NH ₃ oxidation increases, so that the NH ₃ oxidation efficiency sensitive temperature interval of the SDPF is set as [350 ℃ and +infinity);

The actual SDPF operating characteristics do not guarantee that the above-mentioned division of temperature intervals is continuous throughout the temperature axis, but in order to meet control requirements, the division of the SDPF temperature intervals should be seamless. The present invention therefore selects the temperature interval division scheme shown in fig. 2 as the preferred embodiment of the present invention only.

Referring to fig. 5, the operating state of the SCR is divided into 4 temperature intervals according to the carrier temperature according to the operating characteristics of the selected SCR system. The method comprises a DeNOx ineffective zone of the SCR, a DeNOx efficiency sensitive zone of the SCR, a high-efficiency conversion zone of the SCR and an NH ₃ oxidation efficiency sensitive zone of the SCR respectively.

Wherein, the DeNOx ineffective zone of the SCR is determined by the lowest temperature at which hydrolysis and pyrolysis reactions of urea can occur, so the temperature range is (-273 ℃ and 185 ℃);

The DeNOx efficiency sensitive temperature interval, the high-efficiency conversion interval and the NH ₃ oxidation efficiency sensitive temperature interval of the SCR are obtained by developing DeNOx efficiency tests of the SCR under different conditions of temperature, airspeed, ammonia storage amount and NO ₂/NO_x proportion. When the temperature of the SCR carrier is higher than 250 ℃, the DeNOx efficiency on the SCR is not increased along with the temperature rise, and the airspeed, the ammonia storage amount and the NO ₂/NO_x proportion have NO influence on the DeNOx efficiency any more, so the temperature range of a DeNOx efficiency sensitive temperature interval is set to be [185 ℃ and 250 ℃), when the temperature of the SCR carrier is higher than 350 ℃, the NH ₃ oxidation phenomenon on the SCR starts to appear, and the NH ₃ oxidation occurrence degree is increased along with the temperature rise, so the NH ₃ oxidation efficiency sensitive temperature interval of the SCR is set to be [350 ℃ and + ];

The actual SCR operating characteristics cannot ensure that the above-mentioned division of the temperature interval is continuous over the entire temperature axis, but in order to meet the control requirements, the division of the SCR temperature interval should be seamless. The present invention therefore selects the temperature interval division scheme shown in fig. 3 as the preferred embodiment of the present invention only.

Step S04, acquiring the current carrier temperatures of the SCR and the SDPF at intervals of a first preset time, and executing a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and the SDPF so as to calculate and obtain target injection amounts of the first nozzle and the second nozzle according to the target reductant strategy;

Wherein, nozzle one corresponds with SDPF, nozzle two corresponds with SCR.

Referring to fig. 7, the SDPF carrier temperature model is built similar to the DOC carrier temperature model, but only the thermodynamic part and not the HC oxidation exotherm are considered, and the model takes the SDPF inlet temperature sensor measurement, the SDPF outlet temperature sensor measurement and the exhaust mass flow signal as inputs, and the SDPF carrier temperature is obtained after model calculation. The reductant supply control system will not supply reductant when the monitored SDPF carrier temperature is in a DeNOx inactive zone of the SDPF, will switch to a class A reductant supply control state when the monitored SDPF carrier temperature enters a DeNOx efficiency sensitive zone of the SDPF, will switch to a class B reductant supply control state when the monitored SDPF carrier temperature enters a passive regeneration efficiency sensitive zone of the SDPF, and will switch to a class C reductant supply control state when the monitored SDPF carrier temperature enters an NH ₃ oxidation efficiency sensitive zone of the SDPF.

Referring to FIG. 8, when the system enters the A-type reductant supply control state control, the upstream reductant supply rate is allocated with the DeNOx efficiency on the SDPF as the main control target, and the downstream SCR is replenished if the DeNOx efficiency on the SDPF is insufficient, the DeNOx efficiency sensitive area of the SDPF is generally within the range of 180-250 ℃, the reductant can start to be injected, the SCR reaction efficiency is greatly affected by the temperature, the airspeed, the ammonia storage amount and the NO ₂/NO_x ratio, and the temperature of the SDPF carrier is low at this time, and the passive regeneration hardly has the reaction condition, so the control target of the reductant supply strategy is to maximize the DeNOx efficiency on the SDPF.

Under this control strategy, the control system first takes as input a real-time stored NH ₃ quantity signal, an SDPF inlet NO ₂ concentration signal, an SDPF carrier temperature signal, an SDPF inlet NO _x concentration signal, an exhaust mass flow signal, and an inlet NH ₃ concentration signal, calculates a real-time stored NH ₃ quantity, a real-time DeNO _x efficiency of the SDPF catalyst, an SDPF outlet NO _x concentration, an SDPF outlet NO ₂ concentration, and an SDPF outlet NH ₃ concentration using the established SCR chemical reaction kinetics model of the SDPF.

The method comprises the steps of updating a model input by real-time NH ₃ quantity, calculating a urea injection quantity demand value of a No. 1 nozzle through the real-time DeNO _x efficiency of an SDPF catalyst, and calculating DeNO _x efficiency of the SCR catalyst through an SCR chemical reaction kinetic model by taking the concentration of NO _x at an outlet of the SDPF, the concentration of NO ₂ at an outlet of the SDPF and the concentration of NH ₃ at an outlet of the SDPF as inputs in combination with the SCR carrier temperature of the real-time NH ₃ quantity of SCR and the exhaust gas mass flow.

Referring to fig. 9, when the system enters the control state control of the B-type reducing agent supply, the passive regeneration efficiency on the SDPF will introduce a control target, and meanwhile, the downstream SCR carrier temperature interval needs to be determined, and different correction coefficients f need to be introduced for the maximum DeNOx efficiency of the model corresponding to different SCR carrier temperature intervals, in this embodiment, f=0 in the DeNOx ineffective interval of the SCR, f=0.5 in the DeNOx efficiency sensitive interval of the SCR, f=0.9 in the high efficiency conversion interval of the SCR, and f=1.0 in the NH ₃ oxidation efficiency sensitive interval of the SCR;

The current urea injection control strategy is described below taking the SCR in the DeNOx efficiency sensitive zone in the B-type reductant supply control state as an example. In order to avoid emissions exceeding regulatory limits due to the inability of downstream SCRs to fully convert NOx at the SDPF outlet when the SCR is in the DeNOx efficiency sensitive region, it is common to have only the downstream SCRs assume a conversion target of 50% of its current maximum DeNOx capacity, and if the SCR's maximum DeNOx efficiency is η _{SCR_Max} and the control limit under this target operating condition is C _{NOxTp_Lim}, then the NOx emission concentration at the SDPF outlet, C _{NOxSDPFDs_Lim}, should satisfy the following relationship:

C_{NOxSDPFDs_Lim}≤C_{NOxTp_Lim}/（1-η_{SCR_Max}×f)

the reductant pre-control settings for the upstream SDPF should satisfy the following relationship:

ANR≥(C_NOxEo- C_{NOxTp_Lim}/（1-η_{SCR_Max}×f））/ C_NOxEo

Wherein η _{SCR_Max} is calculated by an SCR chemical reaction kinetic model, f=0.5 when the SCR is in a DeNOx efficiency sensitive interval;

Judging the temperature interval of the SCR carrier, and confirming the dependence relationship between the temperature of the SCR carrier and the 4 SCR temperature intervals by comparing;

The SCR carrier temperature is obtained through an SCR carrier temperature pre-estimation model, and the establishment mode and the parameter identification mode of the SCR carrier temperature model are similar to the thermodynamic part of the DOC model.

Referring to FIG. 10, when the system enters the class C reductant supply control state control, the control strategy is primarily aimed at downstream DeNOx efficiency because the degree of NH ₃ oxidation injected at the inlet of the SDPF increases with increasing temperature, and it is desirable to minimize the amount of reductant injected at the inlet of the SDPF. Each individual DeNOx system in a dual injection system typically does not have a largely redundant design, where the downstream SCR may not have the volume to completely eliminate engine out NOx emissions. Thus, when entering the NH ₃ oxidation efficiency sensitive zone of the SDPF, the control system will first calculate the SCR maximum conversion capability at the current temperature and airspeed via the downstream SCR chemical reaction kinetics model, then calculate the urea injection quantity control target for the 2# nozzle based on the engine outlet NOx concentration and the exhaust mass flow meter, and calculate the urea injection quantity for the 1# nozzle of the SDPF inlet based thereon.

Referring to FIG. 11, a schematic diagram of a reductant co-efficient dispensing system for a dual-stage urea injection system in accordance with a second embodiment of the present invention is shown, the system comprising:

A model construction module 10 for confirming a catalytic unit constitution of the target aftertreatment system to establish a corresponding thermodynamic model including a convective heat transfer model, a thermal conduction model, and a thermal radiation model and a chemical reaction kinetics model including an NO oxidation reaction model, a CRT reaction model, and an SCR chemical reaction kinetics model for the catalytic unit;

A parameter identification module 20, configured to perform parameter identification of each thermodynamic model and each chemical reaction kinetic model through a sample test, where the parameters include a convective heat transfer coefficient, a thermal conductivity coefficient, a specific heat capacity, a thermal radiation/heat transfer coefficient, a chemical reaction activation energy, a chemical reaction pre-factor, and a reaction temperature;

The temperature division module 30 is configured to build an engine test bench to perform a performance bottoming test on the SCR and the SDPF, and divide the carrier temperatures of the SCR and the SDPF into four continuous temperature intervals according to a bottoming test result, wherein the four temperature intervals corresponding to the SCR are a DeNO _x invalid interval of the SCR, a DeNO _x efficiency sensitive interval of the SCR, a high-efficiency conversion interval of the SCR, and an NH ₃ oxidation efficiency sensitive interval of the SCR in sequence, and the four temperature intervals corresponding to the SDPF are a DeNO _x invalid interval of the SDPF, a DeNO _x efficiency sensitive interval of the SDPF, a passive regeneration efficiency sensitive interval of the SDPF, and an NH ₃ oxidation efficiency sensitive interval of the SDPF in sequence;

The injection control module 40 is configured to obtain current carrier temperatures of the SCR and the SDPF at intervals of a first preset time, and execute a corresponding target reductant distribution strategy according to the current carrier temperatures of the SCR and the SDPF, so as to calculate a target injection quantity 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.

Further, the injection control module 40 further includes:

A second injection demand calculation unit for taking the concentration of the SDPF outlet NO _x, the concentration of the SDPF outlet NO ₂ and the concentration of the SDPF outlet NH ₃ in combination with the SCR real-time NH ₃ amount SCR carrier temperature and the exhaust mass flow as inputs of a model, calculating DeNO _x efficiency of the SCR catalyst by the SCR chemical reaction kinetics model, and calculating a urea injection demand of the No. two nozzle by DeNO _x efficiency of the SCR catalyst;

Calculating a urea injection quantity demand value of the No. two nozzle according to the exhaust gas mass flow, the target DeNO _x efficiency of the SCR catalyst and the target DeNO _x concentration of the SCR catalyst inlet;

And calculating the SCR maximum conversion capacity under the current temperature and airspeed through a downstream SCR chemical reaction kinetic model, and calculating the urea injection quantity of the No. two nozzle based on the concentration of NO _x at the engine outlet and an exhaust mass flow meter.

A third control state execution unit for switching the system to the class C reductant supply control state when the SDPF carrier temperature is monitored to enter the NH ₃ oxidation efficiency sensitive zone of the SDPF.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. A method for synergistic efficient distribution of reductant for a dual stage urea injection system, the method comprising:

2. The method for collaborative efficient distribution of reductant for a dual-stage urea injection system according to claim 1, wherein the steps of obtaining current carrier temperatures of SCR and SDPF at intervals of a first preset time, and executing a corresponding target reductant distribution strategy according to the current carrier temperatures of SCR and SDPF to calculate a target injection amount of nozzle one and nozzle two according to the target reductant strategy, the nozzle one corresponding to SDPF, the nozzle two corresponding to SCR, include:

3. The method for collaborative efficient distribution of reductant for a dual-stage urea injection system according to claim 1, wherein the steps of obtaining current carrier temperatures of SCR and SDPF at intervals of a first preset time, and executing a corresponding target reductant distribution strategy according to the current carrier temperatures of SCR and SDPF to calculate a target injection amount of nozzle one and nozzle two according to the target reductant strategy, the nozzle one corresponding to SDPF, the nozzle two corresponding to SCR further comprise:

4. The reductant co-efficient dispensing method for a dual-stage urea injection system of claim 3, wherein if the maximum DeNOx efficiency of the SCR catalyst is ηscr_max, the NO _x emission concentration C _{NOxSDPFDs_Lim} at the SDPF outlet satisfies the following relationship:

C_{NOxSDPFDs_Lim}≤C_{NOxTp_Lim}/（1-η_{SCR_Max}×f)

C _{NOxTp_Lim} is a control limit value, and f is a correction coefficient.

5. The method for collaborative efficient distribution of reductant for a dual-stage urea injection system according to claim 1, wherein the steps of obtaining current carrier temperatures of SCR and SDPF at intervals of a first preset time, and executing a corresponding target reductant distribution strategy according to the current carrier temperatures of SCR and SDPF to calculate a target injection amount of nozzle one and nozzle two according to the target reductant strategy, the nozzle one corresponding to SDPF, the nozzle two corresponding to SCR further comprise:

6. A reductant co-efficient dispensing system for a dual stage urea injection system, the system comprising:

7. The reductant co-efficient dispensing system for a dual-stage urea injection system of claim 6, wherein the injection control module further comprises:

8. The reductant co-efficient dispensing system for a dual-stage urea injection system of claim 7, wherein the injection control module further comprises:

9. The reductant co-efficient dispensing system for a dual-stage urea injection system of claim 7, further comprising:

C_{NOxSDPFDs_Lim}≤C_{NOxTp_Lim}/（1-η_{SCR_Max}×f)

C _{NOxTp_Lim} is a control limit value, and f is a correction coefficient.

10. The reductant co-efficient dispensing system for a dual-stage urea injection system of claim 8, wherein the injection control module further comprises:

A third control state execution unit for switching the system to a class C reductant supply control state when the SDPF carrier temperature is monitored to enter an NH ₃ oxidation efficiency sensitive zone of the SDPF;