Dual-scr urea injection and fuel injection collaborative control method

Abstract

The application discloses a double-SCR urea injection and fuel injection cooperative control method, which comprises the following steps: when the carbon load and the pressure difference are less than a threshold value, the urea injection of a front-stage SCR and a rear-stage SCR is controlled in stages according to the temperature of the front-stage SCR: when the temperature is a first preset temperature, the front-stage SCR is mainly injected; when the temperature is a second preset temperature, the rear-stage SCR is mainly injected; and when the temperature is a third preset temperature, within the ammonia coverage range of the rear-stage SCR, the injection proportion of the front-stage SCR and the rear-stage SCR is adjusted based on the sliding mode error rate of the front-stage SCR; when the carbon load or the pressure difference is greater than a certain threshold value, the DPF is actively regenerated, the fuel injection amount is dynamically adjusted based on the temperature change of the DPF to adjust the nozzle opening degree, within the ammonia coverage range of the rear-stage SCR, the NO x The outlet concentration, the carrier temperature of the front-stage SCR and the sliding mode error rate of the front-stage SCR are used to correct the urea injection amount of the front-stage SRR. The application can efficiently remove harmful nitrogen oxides.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of urea injection and fuel injection control, in particular to a double-SCR urea injection and fuel injection collaborative control method. BACKGROUND

[0002] Diesel engines are widely used due to their unique advantages, but nitrogen oxides (NO x ) in diesel engine exhausts are extremely harmful due to their participation in the formation of photochemical smog. In order to reduce the impact of heavy-duty diesel vehicle emissions on the environment, urea selective catalytic reduction technology (Urea Selective Catalytic Reduction, Ure-SCR) has become one of the most effective technologies for reducing NO x emissions.

[0003] A large number of studies have shown that when the engine is at low load, low exhaust temperature is not conducive to the conversion of NO X by SCR, and is not conducive to the reduction reaction of harmful nitrogen oxides by SCR, so under normal circumstances, post-injection in the cylinder is required to increase the exhaust temperature after the turbine, which results in waste of diesel and urea.

[0004] Therefore, the current major manufacturers develop the next stage of aftertreatment technology route ccSCR+DOC+DPF+SCR route, and for the new structure ccSCR+DOC+DPF+SCR route, the fuel post-injection nozzle is arranged after the front-stage SCR (ccSCR), based on this structure, the technology of double-SCR urea and fuel injection control is unreasonable in collaborative control distribution, resulting in urea leakage and pollution of the environment. SUMMARY

[0005] The present application is aimed at the problems of urea leakage, ammonia coverage fluctuation, and low fuel injection coupling efficiency in the process of NOx emission control and DPF regeneration in the existing diesel engine exhaust aftertreatment system, and provides a double-SCR urea injection and fuel injection collaborative control method, which aims to achieve an optimized balance between high-efficiency conversion and resource consumption of NO x . The method controls the injection amount of urea of the front-stage and rear-stage SCR and collaboratively controls the fuel injection of the DPF active regeneration system, thereby achieving high-efficiency removal of harmful nitrogen oxides, ensuring that the DPF does not produce HC poisoning phenomenon, reducing urea leakage and fuel injection amount, and improving the economy of the aftertreatment system.

[0006] The present application is achieved by the following technical solutions:

[0007] The dual-SCR urea injection and fuel injection coordinated control method is based on an exhaust aftertreatment system composed of ccSCR+DOC+DPF+SCR technology. This exhaust aftertreatment system consists of a ccSCR (pre-stage SCR), a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a post-stage SCR arranged sequentially in the exhaust manifold, including:

[0008] Monitor the temperature of the upstream SCR, the temperature of the DPF, the carbon loading, and the pressure difference;

[0009] When the carbon loading and pressure difference are less than their respective thresholds, the urea injection of the pre-stage SCR and the post-stage SCR is controlled in stages according to the monitored temperature of the pre-stage SCR: at the first preset temperature, urea injection is carried out in the pre-stage SCR-dominant mode; at the second preset temperature, urea injection is carried out in the post-stage SCR-dominant mode; at the third preset temperature, within the range of the ammonia coverage of the post-stage SCR, the injection ratio of the pre-stage SCR and the post-stage SCR is adjusted based on the calculated sliding mode error rate of the pre-stage SCR.

[0010] When the carbon load or pressure difference exceeds its respective threshold, the DPF actively heats up, dynamically adjusting the fuel injection nozzle opening based on the DPF's temperature change rate and performing feedforward compensation; urea injection is then performed in the subsequent SCR-dominated mode, and within the range of the subsequent SCR ammonia coverage, urea injection is based on NO... x The outlet concentration, the carrier temperature of the pre-stage SCR, and the calculated sliding mode error rate of the pre-stage SCR are used to correct the urea injection amount of the pre-stage SCR.

[0011] Specifically, in the pre-stage SCR-dominated mode, the proportion of urea injection by the pre-stage SCR to the total urea injection of the pre-stage SCR and the post-stage SCR is at least greater than 90%; in the post-stage SCR-dominated mode, the proportion of urea injection by the post-stage SCR to the total urea injection of the pre-stage SCR and the post-stage SCR is at least greater than 90%.

[0012] Among them, the dynamic adjustment of fuel injection quantity and nozzle opening based on the DPF temperature change rate is achieved by controlling the nozzle opening within the nozzle opening range based on the temperature deviation between the target DPF temperature and the actual DPF temperature, using a PID closed loop. The following model is employed:

[0013] ;

[0014] ;

[0015] ;

[0016] In the formula, The opening degree is based on the regeneration temperature correction time; This indicates the amount of fuel injected by the feedforward control output. represents a feedforward gain, represents a DPF temperature represents a rate of change of the DPF temperature, represents a fuel injection adjustment amount of a PID controller output, is a control parameter of a fuel injection nozzle opening degree, is a temperature deviation; is an opening degree integral control coefficient, is an opening degree differential control coefficient; represents a final output fuel injection amount, is an integral term of an error, is a rate of change of the error, de(t) is a differential time, represents a DPF temperature rate of change.

[0017] Wherein, during the third preset temperature and the active warming period, when the ammonia coverage rate of the rear SCR is monitored to exceed the set threshold value, the SMC controller calculates the sliding mode error rate of the front SCR, and adjusts the injection ratio of the front SCR and the rear SCR based on the sliding mode error rate of the front SCR.

[0018] Wherein, the SMC controller restricts the ammonia coverage rate tracking error of the rear SCR within a preset threshold value through the sliding mode error rate of the front SCR, so that the ammonia coverage rate of the rear SCR is at the set threshold value, to balance the reaction rate:

[0019] The ammonia coverage rate of the rear SCR and its time rate of change are calculated by the following formula:

[0020] ;

[0021] - - - - ;

[0022] In the formula, represents the ammonia coverage rate of the rear SCR, represents the corresponding time rate of change, 、 、 、 represents the reaction rate constant of the positive reaction of urea water hydrolysis to generate ammonia, ammonia desorption reaction, standard SCR reaction, fast SCR reaction, slow SCR reaction and ammonia oxidation side reaction, represents the inlet ammonia concentration of the rear SCR, 、 represents the outlet NO x component concentration,

[0023] Let Let the control variable U be the ammonia concentration, and let the expected value of X1 be... Let the sliding surface tracking error be The tracking error of ammonia coverage rate is controlled within a preset threshold.

[0024] During the active heating period of the DPF, a coordinated control mode of urea injection quantity between the pre-stage SCR and the post-stage SCR is adopted, combined with the NO at the outlet of the post-stage SCR. x The outlet concentration, the carrier temperature of the pre-stage SCR, and the calculated sliding error rate of the pre-stage SCR are used to correct the urea injection amount of the pre-stage SCR.

[0025] During the active heating period of the DPF, the NO at the outlet of the subsequent SCR is... x The outlet concentration is used to dynamically adjust the urea injection rate of the upstream SCR. If the ammonia coverage of the downstream SCR exceeds the set threshold, the urea injection rate of the downstream SCR is reduced, and the urea injection rate of the upstream SCR is adjusted, including reducing the urea injection rate of the upstream SCR.

[0026] Among them, NO, controlled by PID, passes through the output of the subsequent SCR. x The outlet concentration feedback dynamically corrects the urea injection rate of the upstream SCR, including:

[0027] ;

[0028] (k);

[0029] ;

[0030] in, This indicates the output urea injection volume. , , These are the proportional, integral, and derivative parameters of the PID controller. for Urea injection volume at any given time for NO at any moment x Conversion error, for NO at any moment x Conversion error, NO at time k-2 x Conversion error, This indicates the amount of feedforward compensation. Indicates feedforward gain. This represents the rate of change of DPF temperature within two adjacent control periods, K and K+1.

[0031] The first preset temperature is less than 200 DEG C, the second preset temperature is greater than or equal to 200 DEG C and less than 250 DEG C, and the third preset temperature is greater than or equal to 250 DEG C.

[0032] The NO of the rear SCR x The maximum and minimum values of the outlet concentration and the ammonia coverage rate are calculated by the following formula:

[0033] ;

[0034] ;

[0035] ;

[0036] In the formula, represents the concentration of the NO , represents the maximum value of the ammonia coverage rate, represents the minimum value of the ammonia coverage rate, represents the catalyst volume space velocity, represents the ammonia adsorption kinetic constant, represents the expected ammonia concentration, represents the oxygen concentration, represents the inlet concentration of the NO X , represents the space velocity, represents the NO X conversion efficiency, , represents the reaction rate of the NOX fast reaction and the reaction rate of the N2O, respectively, represents the ammonia storage rate, is the ratio of the NO2 / NO X .

[0037] The diesel engine exhaust aftertreatment double-SCR urea injection and fuel injection cooperative control method of the application controls the fuel injection in the DPF active regeneration process by detecting the temperature value of the DPF, performs injection mainly in the rear SCR during the DPF active regeneration process, and within the ammonia coverage rate range of the rear SCR, based on the NO x outlet concentration, the carrier temperature of the front SCR and the calculated sliding mode error rate of the front SCR, the front SCR urea injection amount is corrected, the double-SCR urea stage and fuel injection are cooperatively controlled, the urea and fuel injection can be accurately controlled, the problems of ammonia leakage and coupling difference existing during the active regeneration are effectively solved, the urea injection and fuel cooperative injection accuracy are ensured, the diesel and urea injection amounts are reduced, the pollutant emissions during the regeneration period do not exceed the limit value, the HC poisoning phenomenon of the DPF during the operation is prevented, and the environmental pollution is reduced.

[0038] The present application can effectively solve the ammonia leakage during the DPF active regeneration by adopting the coordinated control strategy of the front and rear SCR injection amounts, and can control the urea injection amount of the front SCR (ccSCR) with high control precision, reduce the diesel injection amount and environmental pollution, provide an effective solution for reducing the ammonia leakage of the dual-ammonia SCR aftertreatment system, improve the conversion efficiency of NO X , and reduce the emission of laughing gas. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a schematic diagram of a diesel engine exhaust aftertreatment system to which the method of the embodiment of the present application is applied.

[0040] Figure 2 is a flowchart of the dual-SCR urea injection and fuel injection coordinated control method of the embodiment of the present application. DETAILED DESCRIPTION

[0041] The present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0042] TERMS EXPLANATION:

[0043] ccSCR: single SCR unit, used for low-temperature stage fast ignition, referred to as front SCR in the present application.

[0044] DOC: diesel oxidation catalyst, used for oxidizing CO and HC (hydrocarbon).

[0045] DPF: diesel particulate filter, used for trapping PM and supporting active regeneration.

[0046] SCR: SCR unit downstream of the DPF, arranged in series to expand the temperature window, referred to as rear SCR in the present application.

[0047] In the urea selective catalytic reduction system, the working principle of the catalyst is as follows:

[0048] When the urea aqueous solution is injected into the inlet of the SCR system, the urea aqueous solution is decomposed into gaseous ammonia under high temperature conditions. The decomposition process will undergo three steps of thermal chemical conversion, namely urea dissolution evaporation, thermal decomposition and isocyanic acid hydrolysis; thereafter, the generated gaseous ammonia will be adsorbed on the active sites of the catalyst and simultaneously undergo dissociation reaction; finally, NO X will react with ammonia under the action of the catalyst to generate water and nitrogen. The above reaction equations are as follows:

[0049] Urea evaporation reaction:

[0050] (1)

[0051] Urea hydrolysis reaction:

[0052] (2);

[0053] Isocyanic acid hydrolysis reaction:

[0054] (3);

[0055] Ammonia adsorption and desorption reaction:

[0056] wherein, refers to active sites in the catalyst

[0057] (4);

[0058] The adsorbed ammonia promotes the reduction of nitrogen oxides mainly through three ways:

[0059] (5);

[0060] (6);

[0061] (7);

[0062] Because NO accounts for more than 90% of NO X , formula (5) is called the standard SCR reaction. Formula (6) is the fast SCR reaction, which has a much faster reaction rate than the standard reaction. In the case of equimolar amounts of NO and NO2, formula (7) is the slow SCR reaction, which has a lower reaction rate than the pure NO2 reaction. Among them, the forward reaction rate of formula (4) is r1, and the reverse reaction rate is r2. The reaction rates of formula (5), formula (6), and formula (7) are r3, r4, and r5, respectively. The reaction rate equations are as follows:

[0063] ;

[0064] In the above formula, denotes the pre-exponential factor, denotes the activation energy, denotes the thermodynamic temperature, corresponds to the reaction rate of the i-th reaction.

[0065] Considering the oxidation reaction of ammonia at high temperatures, the reaction equation is as follows:

[0066] ;

[0067] ;

[0068] ;

[0069] Therefore, the reaction rate equation of the oxidation reaction of ammonia generated at high temperature is:

[0070] ;

[0071] In the formula, represents the activation energy of the oxidation reaction of ammonia generated at high temperature, represents the pre-exponential factor of the oxidation reaction of ammonia generated at high temperature, represents the reaction rate of the oxidation reaction of ammonia generated at high temperature.

[0072] The control method of the embodiment of the application is based on a diesel engine exhaust aftertreatment system adopting a technical route of ccSCR+DOC+DPF+SCR, which is composed of a ccSCR as a front-stage SCR, a diesel oxidation catalyst DOC, a diesel particulate filter DPF, and a rear-stage SCR arranged in the exhaust pipe in sequence, as shown in the accompanying drawings. Figure 1 The ccSCR+DOC+DPF+SCR technical processing route has temperature sensors (such as a first temperature sensor 21, a second temperature sensor 22, a third temperature sensor 23, a fourth temperature sensor 24, and a fifth temperature sensor 25) and pressure sensors (such as a first pressure sensor 11, a second pressure sensor 12, a third pressure sensor 13, a fourth pressure sensor 14, and a fifth pressure sensor 15) for detecting the exhaust gas in real time before and after the ccSCR, the DPF, and the SCR, and NOx sensors (such as a first NOx sensor 31, a second NOx sensor 32, a third NOx sensor 33, and a fourth NOx sensor 34) for detecting the exhaust gas. X X X X X A first nozzle 41 and a second nozzle 32 connected to a urea pump are arranged to control the urea injection of the ccSCR and the SCR, respectively, a third nozzle 43 connected to fuel is arranged to control the fuel injection of the DPF, and a control unit (ECU) is used to control the injection of urea and fuel.

[0073] In the embodiment of the application, the control unit (ECU) integrates a multi-source data acquisition module and a control algorithm module, processes the signals collected by the sensors in real time, and outputs the instructions for urea and / or fuel injection according to the control strategy. In the exemplary embodiment of the application, the double-SCR urea injection and fuel injection cooperative control method is used to accurately control the urea and fuel injection, especially at the moment when the DPF is actively heated, to ensure efficient conversion of NOx while preventing ammonia leakage.

[0074] Referring to​​​​Figure 2 As shown, the dual-SCR urea injection and fuel injection cooperative control method of the embodiment of the application includes: monitoring the temperature of the front-stage SCR, the temperature, carbon loading and pressure difference of the DPF; when the carbon loading and pressure difference are less than the respective threshold values, controlling the urea injection of the front-stage SCR and the rear-stage SCR according to the monitored temperature of the front-stage SCR: at a first preset temperature, performing urea injection in the front-stage SCR dominant mode, at a second preset temperature, monitoring the injection amount of the rear-stage SCR in real time and the NOx conversion rate of the front-stage SCR, and performing urea injection in the rear-stage SCR dominant mode; and at a third preset temperature, within the range (maximum value and minimum value) of the ammonia coverage rate of the rear-stage SCR, adjusting the injection proportion of the front-stage SCR and the rear-stage SCR based on the sliding mode error rate of the front-stage SCR, and increasing or improving the urea injection amount of the front-stage SCR to prevent ammonia leakage; wherein, when the carbon loading or the pressure difference is greater than the respective threshold value, entering the DPF active regeneration mode, actively heating the DPF, dynamically adjusting the fuel injection nozzle opening degree based on the temperature change rate of the DPF and performing feedforward compensation, and controlling the DPF nozzle to perform fuel injection; in the DPF active heating, urea injection is performed in the rear-stage SCR dominant mode, within the range of the ammonia coverage rate of the rear-stage SCR, the NOx conversion rate of the rear-stage SCR, the carrier temperature of the front-stage SCR and the calculated sliding mode error rate of the front-stage SCR are used to correct the urea injection amount of the front-stage SCR. X x

[0075] In the embodiment of the application, in the running process, the temperature of the front-stage SCR is monitored in real time, and the injection state of the front-stage SCR and the rear-stage SCR is controlled based on the above-mentioned strategy according to the temperature of the front-stage SCR, wherein the third preset temperature is the injection cooperative control of the front-stage SCR and the rear-stage SCR, and the first preset temperature and the second preset temperature are the front-stage SCR dominant and the rear-stage SCR dominant respectively.

[0076] In the active regeneration mode, the DPF is actively heated, the fuel injection amount is dynamically adjusted based on the temperature change rate of the DPF to adjust the nozzle opening degree and perform feedforward compensation, within the range of the maximum value and the minimum value of the ammonia coverage rate, the NOx conversion rate of the rear-stage SCR, the carrier temperature of the front-stage SCR and the calculated sliding mode error rate of the front-stage SCR are used to correct the urea injection amount of the front-stage SCR. x

[0077] In the embodiment of the application, the pressure difference of the DPF can be calculated by the pressures measured by the third pressure sensor 13 and the fourth pressure sensor 14 arranged at the inlet and the outlet of the DPF, for example, as follows: Figure 1 As shown, the carbon loading threshold value (msoot) can be 5 g / L, and the pressure difference threshold value (ΔP) can be 15 kPa.

[0078] ​​​In the embodiment, in the front SCR dominant mode, the urea injection amount of the front SCR is at least greater than 90% or higher of the total urea injection amount of the front SCR and the rear SCR; in the rear SCR dominant mode, the urea injection amount of the rear SCR is at least greater than 90% or higher of the total urea injection amount of the front SCR and the rear SCR.

[0079] In the embodiment, the fuel injection nozzle opening degree is dynamically adjusted based on the temperature change rate of the DPF, and feedforward compensation is performed, the DPF nozzle is controlled to perform fuel injection, which is based on the temperature deviation between the DPF target temperature and the obtained DPF actual temperature, and the nozzle opening degree of the third nozzle 43 is controlled by closed-loop PID control in the nozzle opening degree range, to ensure stable regeneration temperature and reduce HC poisoning risk. In the embodiment, the upper limit and the lower limit of the opening degree of the third nozzle 43 are preset, and in the closed-loop PID control, the control parameters of the opening degree of the third nozzle 43 are controlled within the range of the upper limit and the lower limit of the opening degree.

[0080] In the embodiment, the fuel injection control of the DPF nozzle is performed by using the feedforward-feedback compound control mode, which can use the following model:

[0081] The feedforward control formula is as follows: ;

[0082] The fuel injection control formula is as follows:

[0083] ;

[0084] ;

[0085] In the formula, is the opening degree based on the regeneration temperature correction time; represents the fuel injection amount of the feedforward control output, represents the feedforward gain, represents the change rate of the DPF temperature ; represents the fuel injection adjustment amount of the PID controller output, is the control parameter of the fuel nozzle opening degree, is the temperature deviation; is the integral control coefficient of the opening degree, is the differential control coefficient of the opening degree; represents the final output fuel injection amount, is the integral term of the error, is the change rate of the error, de(t) is the differential time, represents the change rate of the DPF temperature.

[0086] In the DPF active warming process, on one hand, the urea injection amount of the front SCR is dynamically corrected according to the outlet concentration of NO x , and if the ammonia coverage rate of the rear SCR is monitored to exceed a threshold value, the urea injection amount of the rear SCR is reduced; on the other hand, the ammonia coverage rate of the rear SCR is estimated according to the temperature rise, the urea injection amount of the rear SCR is corrected based on the calculated sliding mode error rate of the front SCR, and the urea injection amount of the front SCR is feedback adjusted according to the carrier temperature of the front SCR and the conversion efficiency of NO x , so as to realize the cooperative control of the front SCR and the rear SCR.

[0087] After the DPF enters the active regeneration mode, in the active regeneration process, the DPF is in a high temperature stage (above 300 DEG C), the DPF is actively warmed up, the back pressure is reduced, and the particulate matters in the DPF are removed.

[0088] In the first preset temperature, the urea injection is performed in the front SCR dominant mode, in the second preset temperature, the urea injection is performed in the rear SCR dominant mode, the ammonia coverage rate of the rear SCR and the conversion rate of NO x are monitored in real time, when the ammonia coverage rate θ NH3 of the rear SCR is monitored to exceed a set threshold value at the third preset temperature and in the DPF active warming process, the injection amount correction of the front SCR is triggered, the urea injection amount of the front SCR is constrained by the SMC controller, the injection proportion of the front SCR and the rear SCR is adjusted, and the urea injection amount of the front SCR is increased.

[0089] In the third preset temperature and in the DPF active warming process, the SMC controller calculates the sliding mode error rate of the front SCR to constrain the ammonia coverage rate tracking error of the rear SCR within a preset threshold value, so that the ammonia coverage rate of the rear SCR is within a given threshold value, so as to balance the reaction rate, including:

[0090] The ammonia coverage rate of the rear SCR and the time change rate thereof are calculated by the ammonia coverage rate dynamic correction formula;

[0091] ;

[0092] - - - - ; respectively represent the inlet concentration and the outlet concentration of NO X of the rear SCR;

[0093] In the formula, denotes the ammonia coverage rate of the rear SCR, denotes the corresponding time rate of change, , , , denotes the reaction rate constant of the positive reaction of urea hydrolysis to generate ammonia, ammonia desorption reaction, standard SCR reaction, fast SCR reaction, slow SCR reaction and ammonia oxidation side reaction, denotes the ammonia concentration at the inlet of the rear SCR, , denotes the outlet NO x concentration of the rear SCR,

[0094] Let , the control variable U be the ammonia concentration, and the X1 desired value be , let the sliding mode surface tracking error be , control the ammonia coverage rate tracking error within a preset threshold, such as within 5% (≤5%), ensure that the ammonia coverage rate does not exceed the given threshold, and does not cause ammonia leakage, and suppress the NH3 oxidation side reaction (such as generating N2O) at high temperature.

[0095] The embodiments of the present application constrain the ammonia coverage rate tracking error (such as ≤5%) by introducing sliding mode control, dynamically adjust the ammonia injection amount (the corresponding urea injection amount can be derived by the determined ammonia injection amount), and the control effect is more accurate than PID control, has strong robustness, fast dynamic response, is more suitable for the nonlinear system, and also has high disturbance line, and can effectively suppress ammonia leakage.

[0096] In the embodiments of the present application, at the second preset temperature, the NO x conversion efficiency of the rear SCR is above 90%, and plays a leading role. In the embodiments of the present application, at the second preset temperature, the rear SCR plays a leading role, at the third preset temperature, the front SCR injection amount correction program is triggered, and the urea injection amount of the front SCR and the rear SCR is in a cooperative control mode: if the ammonia coverage rate of the rear SCR exceeds the threshold of the ammonia coverage rate corresponding to the third preset temperature, the urea injection amount of the front SCR should be adjusted to avoid overloading of the rear SCR, and ensure that the ammonia coverage rate of the rear SCR does not exceed the given threshold, and does not cause ammonia leakage.

[0097] Specifically, according to the outlet concentration of NO x collected by the sensor in real time, the urea injection amount of the front SCR is dynamically corrected by feedback, when the ammonia coverage rate of the rear SCR exceeds the threshold of the ammonia coverage rate at the temperature, the urea injection amount of the front SCR is adjusted, the urea injection amount of the front SCR and the rear SCR is adjusted to a preset ratio, such as 0.8:0.2, to avoid over-limit of the urea injection amount of the rear SCR, prevent the nozzle of the front SCR from being burnt out, and realize cooperative control of the urea injection amount of the front SCR and the rear SCR.

[0098] In this embodiment, during the active heating of the DPF, the subsequent SCR is the main sprayer. During the active heating of the DPF, a pre-stage SCR spray amount correction program is triggered when the conditions are met. Based on the calculated sliding error rate of the pre-stage SCR, the urea spray amount of the subsequent SCR is corrected. If the ammonia coverage of the subsequent SCR is detected to exceed the threshold, the urea spray amount of the subsequent SCR is reduced, and the urea spray amount of the pre-stage SCR is adjusted, including reducing the urea spray amount of the pre-stage SCR.

[0099] In this embodiment of the application, during the active heating of the DPF, the NO at the outlet of the subsequent SCR is controlled by PID control. x The outlet concentration feedback dynamically corrects the urea injection rate of the upstream SCR. Specifically, it is based on the NO concentration at the downstream SCR outlet. x The outlet concentration is determined by the ECU outputting the corrected urea injection quantity for the pre-stage SCR, causing the first nozzle of the pre-stage SCR to adjust its opening according to the command. A control model can be employed, including:

[0100] ;

[0101] (k);

[0102] The feedforward formula is: ;

[0103] in, This indicates the output urea injection volume. , , These are the proportional, integral, and derivative parameters of the PID controller. for Urea injection volume at any given time for NO at any moment x Conversion error, for NO at any moment x Conversion error, NO at time k-2 x Conversion error, This indicates the amount of feedforward compensation. Indicates feedforward gain. This represents the rate of change of DPF temperature within two adjacent control periods, K and K+1.

[0104] In this embodiment, a stony Kalman filter can be used to predict the internal temperature of the downstream SCR. Based on this temperature, the reaction rate of related reactions can be calculated, and then the ammonia coverage of the downstream SCR can be predicted. This prediction of the downstream SCR's ammonia coverage allows for the prediction of the downstream SCR's injection quantity. Ultimately, this enables coordinated control of the urea injection quantities of both the upstream and downstream SCRs, allowing for advance adjustment of the urea injection ratio between the upstream and downstream SCRs. This effectively solves the ammonia leakage problem during active regeneration, providing high control precision and reducing diesel injection quantity and environmental pollution. It offers an effective solution for reducing ammonia leakage in dual-ammonia SCR aftertreatment systems and improving NOx efficiency. X This improves conversion efficiency and reduces nitrous oxide emissions, while also preventing HC poisoning from the DPF during operation.

[0105] In addition, during active DPF regeneration, the fuel injection quantity is coupled with the internal temperature of the subsequent SCR to help determine the thermal impact of the DPF regeneration process on the subsequent SCR and prevent high temperature from causing ammonia oxidation side reactions.

[0106] In this embodiment of the application, the first preset temperature zone is less than 200°C, the second preset temperature is greater than or equal to 200°C and less than 250°C, and the third preset temperature is greater than or equal to 250°C.

[0107] In this embodiment of the application, the NO of the subsequent SCR x The maximum and minimum values ​​of the export concentration and ammonia coverage range are calculated as follows:

[0108] ;

[0109] ;

[0110] ;

[0111] In the formula, express The concentration of NO in the subsequent SCR stage. x Export concentration, This represents the maximum ammonia coverage rate. This represents the minimum ammonia coverage rate. Indicates the catalyst volume space velocity. This represents the ammonia adsorption kinetic constant. This indicates the desired ammonia concentration. Indicates oxygen concentration. Indicates NO X The imported concentration, Indicates air velocity, Indicates NO X Conversion efficiency , denotes the reaction rate of the fast reaction of NO X and the reaction rate of N2O, denotes the ammonia storage rate, is the ratio of NO2 / NO X .

[0112] Experimental setup

[0113] I. Sensor and actuator configuration

[0114] Temperature sensor: measurement accuracy ± 5°C, which can be arranged at the inlet of the ccSCR, the inlet of the DPF, the inlet of the SCR, the outlet of the SCR, etc., to monitor the exhaust gas temperature in real time.

[0115] Pressure sensor: range 0-50 kPa, accuracy ± 0.5%.

[0116] NO X sensor; range 0-2000 ppm, accuracy ± 2%.

[0117] First nozzle and second nozzle: urea injection range 0-50 mg / s.

[0118] Third nozzle: injection range 0-100 mg / s.

[0119] II. Graded control strategy under non-DPF active regeneration

[0120] 1. First preset temperature: in the front-stage SCR dominant mode;

[0121] 2. Second preset temperature: in the rear-stage SCR dominant mode, the rear-stage SCR undertakes the main NO x conversion task;

[0122] 3. Third preset temperature: suppress ammonia leakage by sliding mode control (SMC), the sliding mode control constrains the ammonia coverage rate tracking error ( ≤ 5%), and dynamically adjusts the injection amount.

[0123] State variable definition: S1= , S2= ;

[0124] Sliding surface design: = e + λ∫edt=( -0.8) + 0.5∫( -0.8)dt;

[0125] Control law: Urear=−K·sign(s) (sliding mode control gain K=0.2);

[0126] The ECU dynamically adjusts the injection quantity of the subsequent SCR stage based on the sliding surface to ensure... It remained stable at 0.8±0.05.

[0127] Post-SCR ammonia coverage >0.8 triggers pre-stage SCR injection quantity correction.

[0128] III. DPF Active Regeneration Coordinated Control

[0129] 1. Regeneration triggering conditions

[0130] The carbon loading threshold (msoot) is >5 g / L, or the pressure difference threshold ΔP is >15 kPa.

[0131] 2. Fuel Injection Control (PID Feedforward-Feedback)

[0132] formula

[0133] 3. Parameter calibration:

[0134] (Optimized through bench testing).

[0135] 4. Coordinated adjustment of urea injection

[0136] Urea injection is performed in the downstream SCR-dominated mode. Within the ammonia coverage range, a PID controller combined with feedforward compensation is used, based on the NO at the downstream SCR outlet. x The outlet concentration, the carrier temperature of the pre-stage SCR, and the sliding mode error rate of the pre-stage SCR (the sliding mode error rate is controlled in the same way as the sliding mode control technology at the third preset temperature mentioned above) are used to correct the urea injection amount of the pre-stage SCR.

[0137] IV. Implementation Results Verification

[0138] NO x Conversion efficiency: >90% under post-stage SCR-dominated system, >95% under sliding mode control optimization.

[0139] Ammonia leakage control: <0.5ppm (limit 1ppm).

[0140] Urea consumption: Reduced by 12-30% (dynamic allocation strategy).

[0141] DPF regeneration efficiency: carbon load removal rate >98%, back pressure reduction 40%.

[0142] In this embodiment, through multi-sensor data fusion, hierarchical control strategies, and intelligent algorithms (PID, sliding mode control), precise coordination between dual-SCR urea and fuel injection is achieved, effectively suppressing ammonia leakage (<0.5 ppm) and improving NO₂ levels. xConversion efficiency (>95%), while reducing urea and fuel consumption (12-30% reduction), reducing the possibility of DPF HC poisoning, reducing the emission of laughing gas.

[0143] The above shows and describes the basic principles and main features of the present application and the advantages of the present application, it is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application; therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0144] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for coordinated control of dual-SCR urea injection and fuel injection, characterized in that, This exhaust aftertreatment system is based on ccSCR+DOC+DPF+SCR technology. The system consists of a ccSCR (pre-stage SCR), a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a post-stage SCR arranged sequentially in the exhaust manifold. It includes: Monitor the temperature of the upstream SCR, the temperature of the DPF, the carbon loading, and the pressure difference; When the carbon loading and pressure difference are less than their respective thresholds, the urea injection of the pre-stage SCR and the post-stage SCR is controlled in stages according to the monitored temperature of the pre-stage SCR: at the first preset temperature, urea injection is carried out in the pre-stage SCR-dominant mode; at the second preset temperature, urea injection is carried out in the post-stage SCR-dominant mode; at the third preset temperature, within the ammonia coverage range of the post-stage SCR, the injection ratio of the pre-stage SCR and the post-stage SCR is adjusted based on the sliding error rate of the pre-stage SCR. When the carbon load or pressure difference exceeds its respective threshold, the DPF actively heats up, dynamically adjusting the fuel injector opening and providing feedforward compensation based on the DPF's temperature change rate. Urea injection is then performed in the subsequent SCR-dominated mode, within the subsequent SCR ammonia coverage range, based on the NO at the subsequent SCR outlet. x The outlet concentration, the carrier temperature of the pre-stage SCR, and the sliding error rate of the pre-stage SCR are used to correct the urea injection amount of the pre-stage SCR.

2. The dual-SCR urea injection and fuel injection coordinated control method according to claim 1, characterized in that, In the pre-stage SCR-dominant mode, the urea injection volume of the pre-stage SCR accounts for at least 90% of the total urea injection volume of the pre-stage SCR and the post-stage SCR; in the post-stage SCR-dominant mode, the urea injection volume of the post-stage SCR accounts for at least 90% of the total urea injection volume of the pre-stage SCR and the post-stage SCR.

3. The dual-SCR urea injection and fuel injection coordinated control method according to claim 1, characterized in that, The dynamic adjustment of fuel injector opening based on the temperature change rate of DPF and the feedforward compensation is based on the temperature deviation between the target temperature of DPF and the actual temperature of DPF, and the nozzle opening is controlled within the nozzle opening range based on PID closed loop. The following model is used: ； ； ； In the formula, The opening degree is based on the regeneration temperature correction time; This indicates the amount of fuel injected by the feedforward control output. Indicates feedforward gain. Indicates DPF temperature rate of change, This represents the fuel injection adjustment amount output by the PID controller. These are the control parameters for the fuel injector opening. Temperature deviation; The integral control coefficient for opening degree. The differential control coefficient for the opening degree; This indicates the final output fuel injection quantity. The integral term of the error. Let de(t) be the rate of change of the error, and de(t) be the differential time. This indicates the rate of change of DPF temperature.

4. The dual-SCR urea injection and fuel injection coordinated control method according to claim 1, characterized in that, During the third preset temperature and active heating period, when the ammonia coverage of the downstream SCR exceeds the set threshold, the sliding error rate of the upstream SCR is calculated by the SMC controller. Based on the sliding error rate of the upstream SCR, the injection ratio of the upstream SCR and the downstream SCR is adjusted.

5. The dual-SCR urea injection and fuel injection coordinated control method according to claim 4, characterized in that, The SMC controller constrains the ammonia coverage tracking error of the subsequent SCR within a preset threshold by using the sliding mode error rate of the preceding SCR, thus ensuring that the ammonia coverage of the subsequent SCR is within the set threshold to balance the reaction rate. The ammonia coverage ratio and its time-varying rate of change of the subsequent SCR are calculated using the following formula; ； - - - - ； In the formula, This indicates the ammonia coverage ratio of the subsequent SCR stage. This represents the corresponding rate of change over time. , , , The rate constants represent the forward reaction of urea hydrolysis to ammonia, the ammonia desorption reaction, the standard SCR reaction, the fast SCR reaction, the slow SCR reaction, and the ammonia oxidation side reaction. This indicates the ammonia concentration at the inlet of the subsequent SCR stage. , Indicates the NOx component concentration at the outlet. make Let the control variable U be the ammonia concentration, and let the expected value of X1 be... Let the sliding surface tracking error be The tracking error of ammonia coverage rate is controlled within a preset threshold.

6. The dual-SCR urea injection and fuel injection coordinated control method according to claim 5, characterized in that, During the DPF active heating period, a coordinated control mode of urea injection quantity between the upstream SCR and the downstream SCR is adopted, combined with the NO at the outlet of the downstream SCR. x The outlet concentration, the carrier temperature of the pre-stage SCR, and the sliding error rate of the pre-stage SCR are used to correct the urea injection amount of the pre-stage SCR based on the carrier temperature of the pre-stage SCR.

7. The dual-SCR urea injection and fuel injection coordinated control method according to claim 6, characterized in that, During the active heating period of the DPF, the NO at the outlet of the subsequent SCR is... x The outlet concentration is used to dynamically adjust the urea injection rate of the upstream SCR. If the ammonia coverage of the downstream SCR exceeds the set threshold, the urea injection rate of the downstream SCR is reduced, and the urea injection rate of the upstream SCR is adjusted, including reducing the urea injection rate of the upstream SCR.

8. The dual-SCR urea injection and fuel injection coordinated control method according to claim 7, characterized in that, During the DPF active heating period, NO is controlled by PID control at the outlet of the subsequent SCR. x The outlet concentration feedback dynamically corrects the urea injection rate of the upstream SCR, including: ； (k)； ； in, This indicates the output urea injection volume. , , These are the proportional, integral, and derivative parameters of the PID controller. for Urea injection volume at any given time for NO at any moment x Conversion error, for NO at any moment x Conversion error, NO at time k-2 x Conversion error, This indicates the amount of feedforward compensation. Indicates feedforward gain. This represents the rate of change of DPF temperature within two adjacent control periods, K and K+1.

9. The dual-SCR urea injection and fuel injection coordinated control method according to claim 1, characterized in that, The first preset temperature is less than 200℃; the second preset temperature is greater than or equal to 200℃ and less than 250℃; the third preset temperature is greater than or equal to 250℃.

10. The dual-SCR urea injection and fuel injection coordinated control method according to claim 5, characterized in that, NO of the power SCR x The maximum and minimum values ​​of the export concentration and ammonia coverage range are calculated using the following formula: ； ； ； In the formula, express concentration, This represents the maximum ammonia coverage rate. This represents the minimum ammonia coverage rate. Indicates the catalyst volume space velocity. This represents the ammonia adsorption kinetic constant. This indicates the desired ammonia concentration. Indicates oxygen concentration. Indicates NO X The imported concentration, Indicates airspeed. Indicates NO X Conversion efficiency , They represent NO respectively X The reaction rate of fast reaction and the reaction rate of N2O, Indicates ammonia storage rate, NO2 / NO X The ratio of .

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