CN112324547B - Selective catalytic reduction control method and system suitable for mixed fuel - Google Patents

Abstract

The invention relates to a selective catalytic reduction control method and a system suitable for mixed fuel, wherein the method comprises the following steps: obtaining the type of the mixed fuel, and selecting an engine exhaust temperature table and an engine NO according to the type of the mixed fuel_XA discharge meter; obtaining a target ammonia storage amount correction value to obtain a basic target ammonia storage amount, and adding the basic target ammonia storage amount and the target ammonia storage amount correction value considering time delay to obtain a target ammonia storage amount; calculating to obtain the existing ammonia storage amount, and calculating to obtain the ammonia injection correction amount according to the target ammonia storage amount and the existing ammonia storage amount; obtaining a basic ammonia injection quantity, and adding the ammonia injection correction quantity and the basic ammonia injection quantity to obtain an actual ammonia injection quantity; the selective catalytic reduction control is performed based on the actual ammonia injection amount. Compared with the prior art, the NO is optimized when the working condition of the engine suddenly changes_XConversion efficiency and ammonia leakage condition, and the control precision of the selective catalytic reduction system is improved.

Description

Selective catalytic reduction control method and system suitable for mixed fuel

Technical Field

The invention relates to the field of engine emission control, in particular to a selective catalytic reduction control method and system suitable for mixed fuel.

Background

The engine exhaust contains a large amount of nitrogen oxides, NO for short_XThe main components of which are nitric oxide NO and nitrogen dioxide NO₂. Since nitrogen oxides all have varying degrees of toxicity, emission regulations impose specific limits on their emissions. On the current vehicle engine, for NO_XThe control of emissions has mainly used selective catalytic reduction technology, i.e. SCR technology. The most common forms of this technique are: the ammonia gas generated by decomposing the urea aqueous solution is mixed with the tail gas of the engine and enters an SCR (selective catalytic reduction) catalyst, and under the action of the catalyst, the ammonia gas and NO (nitric oxide) are generated_XThe selective catalytic reduction reaction is carried out, and nitrogen and water are generated and then discharged into the atmosphere. The control is mainly based on NO at the inlet of the catalyst_XEmission, spraying different amounts of urea, to NO_XThe discharge amount of the fuel is effectively controlled. However, existing SCR control strategies are based primarily on inlet NO_XWith NO at the outlet_XAnd NH₃PID control of emissions has good effect under steady state conditions, but when the engine operating conditions are switched, NO is suddenly changed_XEmissions can increase or decrease rapidly, resulting in under or over urea injection, triggering of NO_XLow emission conversion rate or excessive ammonia slip. In order to solve the problem, a common method is to establish an ammonia storage model, but when a diesel engine burns mixed fuel, an emission pulse spectrum (table) of an engine changes correspondingly with the change of the fuel, so that the ammonia storage model deviates, the ammonia injection quantity is inconsistent with the actual demand quantity, and the overall conversion efficiency and ammonia leakage are influenced.

Disclosure of Invention

The present invention is directed to overcoming the above-mentioned drawbacks of the prior art and providing a method and system for controlling selective catalytic reduction of a mixed fuel.

The purpose of the invention can be realized by the following technical scheme:

a method for selective catalytic reduction control of a mixed fuel, the method comprising the steps of:

step S1: obtaining the engine speed, the intake pressure of an intake manifold, the selective catalytic reduction temperature, the exhaust flow, the exhaust temperature, the ammonia gas at an inlet and an outlet of the selective catalytic reduction and the NO at the inlet and the outlet of the selective catalytic reduction_X；

Step S2: obtaining the type of the mixed fuel, and selecting an engine exhaust temperature table and an engine NO according to the type of the mixed fuel_XA discharge meter;

step S3: according to the engine speed, the intake manifold intake pressure, the engine exhaust temperature and the engine NO_XObtaining a target ammonia storage amount corrected value considering time delay by the emission table, obtaining a basic target ammonia storage amount according to the selective catalytic reduction temperature and the exhaust flow, and adding the basic target ammonia storage amount and the target ammonia storage amount corrected value considering time delay to obtain a target ammonia storage amount;

step S4: according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the selective catalytic reduction outlet and the NO at the selective catalytic reduction inlet and outlet_XCalculating to obtain the existing ammonia storage amount, and calculating to obtain the ammonia injection correction amount according to the target ammonia storage amount and the existing ammonia storage amount;

step S5: by selective catalytic reduction of inlet and outlet NO_XAnd the exhaust flow rate to obtain a basic ammonia injection amount, and adding the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount;

step S6: the selective catalytic reduction control is performed based on the actual ammonia injection amount.

The type of the mixed fuel of step S2 is obtained by:

acquiring the type of the mixed fuel input by a user;

by selective catalytic reduction of inlet and outlet NO_XThe range to which the amount of discharge belongs acquires the type of the mixed fuel.

In step S3, the basic target ammonia storage amount is obtained by referring to the target ammonia storage amount table based on the selective catalytic reduction temperature and the exhaust gas flow amount.

In step S3, the engine exhaust temperature table and the engine NO are queried according to the engine speed and the intake manifold intake pressure_XEmission table, direction and amount of change of exhaust temperature, and NO_XAccording to the direction and amount of change of the exhaust temperature and NO_XThe target ammonia storage amount correction value considering the time delay is obtained by looking up the table of the change direction and the change amount.

In step S4, according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the outlet of the selective catalytic reduction, and the NO at the inlet and outlet of the selective catalytic reduction_XCalculating to obtain the prior ammonia storage amount K_nThe formula of (1) is:

K_n＝K_n-1+C_urea×Q_Urea-Q_NH3-out-f_{Reaction of}·(Q_NOx-in-Q_NOx-out)

Wherein, K_n-1The ammonia storage amount per unit time, Q_UreaFor urea injection mass flow, C_UreaIs the ammonia concentration of the urea aqueous solution, Q_NH3-outTo export the ammonia concentration, f_{Reaction of}Is the nitrogen-ammonia reaction coefficient, Q_NOx-in、Q_NOx-outRespectively inlet and outlet NO_XMass flow rate.

In step S4, the formula for calculating the ammonia injection correction amount from the target ammonia storage amount and the existing ammonia storage amount is:

Q_correction＝f_{Time constant}×(K_Target-K_n)

Wherein Q is_CorrectionAn ammonia injection amount correction amount; f. of_{Time constant}As adsorption/desorption time coefficient, according to SCR temperature and NH₃Flow rate, obtained from a pulse chart that is calibrated based on SCR ammonia adsorption/release time; k_TargetIs the target ammonia storage amount.

In step S5, port NO is reduced based on selective catalytic reduction_XAnd an exhaust flow rate, the basic ammonia injection amount being obtained by referring to the basic ammonia injection amount table.

In step S5, port NO is reduced according to selective catalyst_XAnd calculating the exhaust gas flow to obtain a basic ammonia injection amount, obtaining a second ammonia injection correction amount according to the instantaneous ammonia leakage amount and the temperature change rate, and adding the second ammonia injection correction amount, the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount.

The calculation formula for obtaining the second ammonia injection correction amount according to the instantaneous ammonia leakage amount and the temperature change rate is as follows:

Q_{second modification}＝Q_{Ammonia slip correction}+Q_{Temperature rise correction}

Ammonia slip correction amount Q of second correction amount_{Ammonia slip correction}According to the magnitude of the instantaneous ammonia leakage, the method is obtained by the following formula:

Q_{ammonia slip correction}＝0(Q_NH3-out＜Q_{Threshold value of ammonia leakage})

Q_{Ammonia slip correction}＝f_{Ammonia slip correction}×(Q_NH3-out-Q_{Threshold value of ammonia leakage})(Q_NH3-out≥Q_{Threshold value of ammonia leakage})

Wherein Q_{Threshold value of ammonia leakage}Is a threshold value of ammonia leakage mass flow, adjusted according to leakage control requirements, f_{Ammonia slip correction}For correcting the coefficient, looking up a table according to the ammonia leakage amount and the exhaust flow;

temperature correction amount Q of second correction amount_{Temperature rise correction}According to the temperature change rate, the temperature change rate is obtained by the following formula:

Q_{temperature rise correction}＝0(ΔT＜ΔT_{Threshold value})

Q_{Temperature rise correction}＝f_{Temperature rise correction}×(K_T0-K_T)(ΔT≥ΔT_{Threshold value})

Wherein Δ T is a temperature increase value per unit time; delta T_{Threshold value}As a threshold value of the rate of temperature rise, f_{Temperature rise correction}For the temperature-rise correction coefficient, the temperature is obtained by looking up a table according to the temperature of the last unit time and the current temperature, K_T0、K_TThe maximum ammonia storage amount of the last unit time temperature and the temperature at the current moment are respectively.

A system for implementing the selective catalytic reduction control method for a mixed fuel, the system comprising:

a mixed fuel type module for obtaining the type of the mixed fuel and selecting an engine exhaust temperature and an engine NO according to the type of the mixed fuel_XA discharge meter;

a target ammonia storage calculation module for calculating the target ammonia storage according to the engine speed, the intake manifold intake pressure, the engine exhaust temperature and the engine NO_XCalculating a target ammonia storage correction value considering time delay according to the emission table, calculating a basic target ammonia storage according to the selective catalytic reduction temperature and the exhaust flow, and adding the basic target ammonia storage and the target ammonia storage correction value considering time delay to obtain a target ammonia storage;

the actual ammonia injection quantity calculation module is used for calculating the actual ammonia injection quantity according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the selective catalytic reduction outlet and the NO at the selective catalytic reduction inlet and outlet_XCalculating to obtain the existing ammonia storage amount, calculating to obtain ammonia injection correction amount according to the target ammonia storage amount and the existing ammonia storage amount, and reducing inlet and outlet NO according to selective catalyst_XAnd calculating the exhaust flow to obtain a basic ammonia injection amount, and adding the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount.

Compared with the prior art, the invention has the following advantages:

(1) according to the engine speed, the intake manifold intake pressure, the engine exhaust temperature and the engine NO_XThe emission table is calculated to obtain a target ammonia storage correction value considering time delay, the target ammonia storage correction value considering time delay based on the change of the working condition of the engine is added, and NO when the working condition of the engine suddenly changes is optimized_XConversion efficiency and ammonia slip.

(2) Obtaining the type of the mixed fuel, and selecting an engine exhaust temperature table and an engine NO according to the type of the mixed fuel_XThe emission table can obtain the fuel condition used by the engine through external input or self-identification, and additionally corrects the target ammonia storage amount according to the type of the fuel, so that the control precision of the selective catalytic reduction system is improved.

Drawings

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a schematic view of a blended fuel type module of the present invention;

FIG. 3 is a schematic diagram of a target ammonia storage calculation module according to the present invention;

FIG. 4 is a schematic diagram of an actual ammonia injection calculation module according to the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

Examples

The embodiment provides a selective catalytic reduction control method suitable for mixed fuel, and aims to solve the problem that when the fuel of an engine is changed, the control cannot be carried out according to the change of the fuel condition, and the control cannot be carried out according to the change of the fuel condition, so that the urea injection is too small or too large, and NO is caused_XLow conversion rate of emission or excessive ammonia slip. As shown in fig. 1, the method comprises the steps of:

step S1: obtaining the engine speed, the intake manifold intake pressure, the selective catalytic reduction temperature,Exhaust flow, exhaust temperature, selective catalytic reduction of inlet and outlet ammonia gas and selective catalytic reduction of inlet and outlet NO_X；

Step S2: obtaining the type of the mixed fuel, and selecting an engine exhaust temperature table and an engine NO according to the type of the mixed fuel_XA discharge meter;

step S3: according to the engine speed, the intake manifold intake pressure, the engine exhaust temperature and the engine NO_XObtaining a target ammonia storage amount corrected value considering time delay by the emission table, obtaining a basic target ammonia storage amount according to the selective catalytic reduction temperature and the exhaust flow, and adding the basic target ammonia storage amount and the target ammonia storage amount corrected value considering time delay to obtain a target ammonia storage amount;

step S4: according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the selective catalytic reduction outlet and the NO at the selective catalytic reduction inlet and outlet_XCalculating to obtain the existing ammonia storage amount, and calculating to obtain the ammonia injection correction amount according to the target ammonia storage amount and the existing ammonia storage amount;

step S5: by selective catalytic reduction of inlet and outlet NO_XAnd the exhaust flow rate to obtain a basic ammonia injection amount, and adding the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount;

step S6: the selective catalytic reduction control is performed based on the actual ammonia injection amount.

Specifically, the method comprises the following steps:

the type of the mixed fuel of step S2 is obtained by: acquiring the type of the mixed fuel input by a user; by selective catalytic reduction of inlet and outlet NO_XThe range to which the amount of discharge belongs acquires the type of the mixed fuel.

In step S3, a basic target ammonia storage amount is obtained by referring to the target ammonia storage amount table based on the selective catalytic reduction temperature and the exhaust gas flow amount.

In step S3, the engine exhaust temperature table and the engine NO are queried based on the engine speed and the intake manifold intake pressure_XEmission table, direction and amount of change of exhaust temperature, and NO_XAccording to the direction and amount of change of the exhaust temperature and NO_XDirection of change ofAnd obtaining a target ammonia storage amount correction value considering time delay by using a variable quantity lookup table.

In step S4, according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the selective catalytic reduction outlet and the NO at the selective catalytic reduction inlet and outlet_XCalculating to obtain the prior ammonia storage amount K_nThe formula of (1) is:

K_n＝K_n-1+C_urea×Q_Urea-Q_NH3-out-f_{Reaction of}·(Q_NOx-in-Q_NOx-out)

Wherein, K_n-1The ammonia storage amount per unit time, Q_UreaFor urea injection mass flow, C_UreaIs the ammonia concentration of the urea aqueous solution, Q_NH3-outTo export the ammonia concentration, f_{Reaction of}Is the nitrogen-ammonia reaction coefficient, Q_NOx-in、Q_NOx-outRespectively inlet and outlet NO_XMass flow rate.

In step S4, the formula for calculating the ammonia injection correction amount from the target ammonia storage amount and the existing ammonia storage amount is:

Q_correction＝f_{Time constant}×(K_Target-K_n)

Wherein Q is_CorrectionAn ammonia injection amount correction amount; f. of_{Time constant}As adsorption/desorption time coefficient, according to SCR temperature and NH₃Flow rate, obtained from a pulse chart that is calibrated based on SCR ammonia adsorption/release time; k_TargetIs the target ammonia storage amount.

In step S5, import/export NO is reduced based on selective catalytic reduction_XAnd an exhaust flow rate, the basic ammonia injection amount being obtained by referring to the basic ammonia injection amount table.

In step S5, port NO is reduced according to selective catalyst_XAnd calculating the exhaust gas flow to obtain a basic ammonia injection amount, obtaining a second ammonia injection correction amount according to the instantaneous ammonia leakage amount and the temperature change rate, and adding the second ammonia injection correction amount, the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount.

The calculation formula for obtaining the second ammonia injection correction amount according to the instantaneous ammonia leakage amount and the temperature change rate is as follows:

Q_{second modification}＝Q_{Ammonia slip correction}+Q_{Temperature rise correction}

Ammonia slip correction amount Q of second correction amount_{Ammonia slip correction}According to the magnitude of the instantaneous ammonia leakage, the method is obtained by the following formula:

Q_{ammonia slip correction}＝0(Q_NH3-out＜Q_{Threshold value of ammonia leakage})

Q_{Ammonia slip correction}＝f_{Ammonia slip correction}×(Q_NH3-out-Q_{Threshold value of ammonia leakage})(Q_NH3-out≥Q_{Threshold value of ammonia leakage})

Wherein Q_{Threshold value of ammonia leakage}Is a threshold value of ammonia leakage mass flow, adjusted according to leakage control requirements, f_{Ammonia slip correction}For correcting the coefficient, looking up a table according to the ammonia leakage amount and the exhaust flow;

temperature correction amount Q of second correction amount_{Temperature rise correction}According to the temperature change rate, the temperature change rate is obtained by the following formula:

Q_{temperature rise correction}＝0(ΔT＜ΔT_{Threshold value})

Q_{Temperature rise correction}＝f_{Temperature rise correction}×(K_T0-K_T)(ΔT≥ΔT_{Threshold value})

Wherein Δ T is a temperature increase value per unit time; delta T_{Threshold value}As a threshold value of the rate of temperature rise, f_{Temperature rise correction}For the temperature-rise correction coefficient, the temperature is obtained by looking up a table according to the temperature of the last unit time and the current temperature, K_T0、K_TThe maximum ammonia storage amount of the last unit time temperature and the temperature at the current moment are respectively.

The embodiment also provides a system for realizing the selective catalytic reduction control method applicable to the mixed fuel, which comprises a mixed fuel type module, a target ammonia storage amount calculation module and an actual ammonia injection amount calculation module.

The brief introduction of each module is as follows:

(1) mixed fuel type module

As shown in FIG. 2, the type of blended fuel may be obtained in three ways, the first being manually by the user via a user interfaceSelecting a currently used fuel; the second is automatic identification by a selection system; and thirdly, when the emission deviation values of a plurality of characteristic working condition points exceed a set threshold value, the system considers that the fuel is switched and triggers automatic correction when the engine is started next time. The second and third methods will obtain corresponding NO through the operation characteristic working condition point when the engine is started and idled_XEmission (or selective catalytic reduction of inlet and outlet NO)_XDischarge amount of) and characteristic operating point NO corresponding to the database_XAnd comparing the emissions to determine the type of the mixed fuel. Fuel characteristic point NO of database_XEmissions, obtained by pre-calibration of the engine using different blends of fuels. After determining the fuel type, reading the engine exhaust temperature and engine NO of the corresponding fuel from the database_XEmission table, engine exhaust temperature table in replacement target ammonia storage amount calculation module, and engine NO_XAnd the emission table is used for finishing data replacement after fuel switching.

(2) Target ammonia storage amount calculation module

As shown in fig. 3, the target ammonia storage amount calculation module first obtains a basic target ammonia storage amount by querying the basic target ammonia storage amount table based on the selective catalytic reduction temperature and the exhaust gas flow amount. Then according to the engine speed and the intake pressure of an intake manifold obtained by an Electronic Control Unit (ECU) of the engine, a table look-up mode is adopted to obtain an engine exhaust temperature table and an engine NO_XObtaining exhaust temperature and NO from emission table_XThe direction and amount of change of (c). And obtaining a target ammonia storage amount correction value considering the time delay through a table look-up. The time from the exhaust manifold to the selective catalytic reduction device is calculated based on the engine exhaust flow rate, and the delay control is performed for the change in the target ammonia storage amount correction value in consideration of the time delay. Based on the above calculation, the corrected target ammonia storage amount at that time is output.

(3) Actual ammonia injection amount calculation module

According to the selective catalytic reduction of port NO as shown in FIG. 4_XAnd the basic ammonia injection amount is obtained by inquiring the basic ammonia injection amount table according to the information such as the exhaust flow rate.

Due to the presence of ammonia at each momentThe reserve change is equal to the difference between the mass flow of ammonia at the inlet and outlet in unit time, and then the difference is subtracted for converting NO_XAmmonia consumed, and therefore urea injection flow rate, ammonia concentration of urea aqueous solution, ammonia concentration at outlet, and selective catalytic reduction inlet and outlet NO_XAnd (4) calculating the ammonia storage change value of each second according to the mass flow, and superposing the ammonia storage amount of one second to obtain the current ammonia storage amount at the current moment.

And comparing the existing ammonia storage amount with the target ammonia storage amount, looking up a table according to an adsorption/desorption time coefficient table calibrated in advance based on ammonia adsorption/desorption time based on a comparison result to obtain a time coefficient, and calculating the ammonia injection amount correction amount by combining the difference value of the ammonia storage amount.

Further, in the case where the instantaneous ammonia leakage amount or the temperature increase amount per unit time exceeds the threshold value in accordance with a sudden change in the operating condition, such as a rapid change in the exhaust temperature, a second ammonia injection correction amount is obtained from the instantaneous ammonia leakage amount and the temperature change rate, and the actual ammonia injection amount is obtained by adding the second ammonia injection correction amount, the ammonia injection correction amount, and the basic ammonia injection amount.

Feasibility and prospect of popularization and application:

the present invention adds an ammonia storage process, and a mixed fuel type module, to the engine in a conventional selective catalytic reduction control. When the engine fuel is switched, the control model can be automatically corrected after the type of the mixed fuel is determined manually or automatically, so that the accuracy of the target ammonia storage amount in the selective catalytic reduction control is improved, and NO when the working condition of the engine suddenly changes is optimized_XConversion efficiency and ammonia slip. The method has operability and has small change on hardware of the selective catalytic reduction system.

Claims (10)

1. A selective catalytic reduction control method for a mixed fuel, comprising the steps of:

step S1: obtaining the engine speed, the intake pressure of an intake manifold, the selective catalytic reduction temperature, the exhaust flow, the exhaust temperature and the ammonia gas at an inlet and an outlet of the selective catalytic reductionAnd selective catalytic reduction of inlet and outlet NO_X；

Step S2: obtaining the type of the mixed fuel, and selecting an engine exhaust temperature table and an engine NO according to the type of the mixed fuel_XA discharge meter;

step S3: according to the engine speed, the intake manifold intake pressure, the engine exhaust temperature and the engine NO_XObtaining a target ammonia storage amount corrected value considering time delay by the emission table, obtaining a basic target ammonia storage amount according to the selective catalytic reduction temperature and the exhaust flow, and adding the basic target ammonia storage amount and the target ammonia storage amount corrected value considering time delay to obtain a target ammonia storage amount;

step S4: according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the selective catalytic reduction outlet and the NO at the selective catalytic reduction inlet and outlet_XCalculating to obtain the existing ammonia storage amount, and calculating to obtain the ammonia injection correction amount according to the target ammonia storage amount and the existing ammonia storage amount;

step S5: by selective catalytic reduction of inlet and outlet NO_XAnd the exhaust flow rate to obtain a basic ammonia injection amount, and adding the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount;

step S6: the selective catalytic reduction control is performed based on the actual ammonia injection amount.

2. The selective catalytic reduction control method for a mixed fuel according to claim 1, wherein the type of the mixed fuel of step S2 is obtained by:

acquiring the type of the mixed fuel input by a user;

by selective catalytic reduction of inlet and outlet NO_XThe range to which the amount of discharge belongs acquires the type of the mixed fuel.

3. The SCR control method of claim 1, wherein the step S3 is performed to obtain the basic target ammonia storage amount by querying the target ammonia storage amount table based on the SCR temperature and the exhaust flow rate.

4. The SCR control method of claim 1, wherein the step S3 queries an engine exhaust temperature table and an engine NO according to the engine speed and the intake manifold intake pressure_XEmission table, direction and amount of change of exhaust temperature, and NO_XAccording to the direction and amount of change of the exhaust temperature and NO_XThe target ammonia storage amount correction value considering the time delay is obtained by looking up the table of the change direction and the change amount.

5. The SCR control method of claim 1, wherein in step S4, the mass flow rate of urea injection, the ammonia concentration of the urea aqueous solution, the ammonia gas at the SCR outlet, and the NOx at the SCR inlet/outlet are determined according to the mass flow rate of urea injection, the ammonia concentration of the SCR aqueous solution, the NOx at the SCR outlet, and the NOx at the SCR inlet/outlet_XCalculating to obtain the prior ammonia storage amount K_nThe formula of (1) is:

K_n＝K_n-1+C_urea×Q_Urea-Q_NH3-out-f_{Reaction of}·(Q_NOx-in-Q_NOx-out)

Wherein, K_n-1The ammonia storage amount per unit time, Q_UreaFor urea injection mass flow, C_UreaIs the ammonia concentration of the urea aqueous solution, Q_NH3-outTo export the ammonia concentration, f_{Reaction of}Is the nitrogen-ammonia reaction coefficient, Q_NOx-in、Q_NOx-outRespectively inlet and outlet NO_XMass flow rate.

6. The selective catalytic reduction control method for a mixed fuel according to claim 1, wherein in step S4, an ammonia injection correction amount Q is calculated from the target ammonia storage amount and the existing ammonia storage amount_CorrectionThe formula of (1) is:

Q_correction＝f_{Time constant}×(K_Target-K_n)

Wherein f is_{Time constant}As adsorption/desorption time coefficient, K_TargetFor a target ammonia storage amount, K_nThe existing ammonia storage amount is adopted.

7. The SCR control method as set forth in claim 1, wherein the step S5 is based on SCR of the NO at the inlet and outlet_XAnd an exhaust flow rate, the basic ammonia injection amount being obtained by referring to the basic ammonia injection amount table.

8. The SCR control method as set forth in claim 1, wherein the step S5 is performed according to SCR of the inlet/outlet NO_XAnd calculating the exhaust gas flow to obtain a basic ammonia injection amount, obtaining a second ammonia injection correction amount according to the instantaneous ammonia leakage amount and the temperature change rate, and adding the second ammonia injection correction amount, the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount.

9. The selective catalytic reduction control method for a mixed fuel according to claim 8, wherein a calculation formula of the second ammonia injection correction amount based on the instantaneous ammonia slip amount and the temperature change rate is:

Q_{second modification}＝Q_{Ammonia slip correction}+Q_{Temperature rise correction}

Ammonia slip correction amount Q of second correction amount_{Ammonia slip correction}According to the magnitude of the instantaneous ammonia leakage, the method is obtained by the following formula:

Q_{ammonia slip correction}＝0(Q_NH3-out＜Q_{Threshold value of ammonia leakage})

Q_{Ammonia slip correction}＝f_{Ammonia slip correction}×(Q_NH3-out-Q_{Threshold value of ammonia leakage}) (Q_NH3-out≥Q_{Threshold value of ammonia leakage})

Wherein: q_{Threshold value of ammonia leakage}Threshold value for mass flow of ammonia leakage quantity, f_{Ammonia slip correction}Is a correction factor;

temperature correction amount Q of second correction amount_{Temperature rise correction}According to the rate of change of the temperature,obtained from the following equation:

Q_{temperature rise correction}＝0 (ΔT＜ΔT_{Threshold value})

Q_{Temperature rise correction}＝f_{Temperature rise correction}×(K_T0-K_T) (ΔT≥ΔT_{Threshold value})

Where Δ T is the temperature rise per unit time, Δ T_{Threshold value}As a threshold value of the rate of temperature rise, f_{Temperature rise correction}For temperature-rise correction factor, K_T0、K_TThe maximum ammonia storage amount of the last unit time temperature and the temperature at the current moment are respectively.

10. A system for implementing the method for selective catalytic reduction control of a mixed fuel according to any one of claims 1 to 9, characterized in that the system comprises:

a mixed fuel type module for obtaining the type of the mixed fuel and selecting an engine exhaust temperature and an engine NO according to the type of the mixed fuel_XA discharge meter;

a target ammonia storage calculation module for calculating the target ammonia storage according to the engine speed, the intake manifold intake pressure, the engine exhaust temperature and the engine NO_XCalculating a target ammonia storage correction value considering time delay according to the emission table, calculating a basic target ammonia storage according to the selective catalytic reduction temperature and the exhaust flow, and adding the basic target ammonia storage and the target ammonia storage correction value considering time delay to obtain a target ammonia storage;

the actual ammonia injection quantity calculation module is used for calculating the actual ammonia injection quantity according to the urea injection mass flow, the ammonia concentration of the urea aqueous solution, the ammonia gas at the selective catalytic reduction outlet and the NO at the selective catalytic reduction inlet and outlet_XCalculating to obtain the existing ammonia storage amount, calculating to obtain ammonia injection correction amount according to the target ammonia storage amount and the existing ammonia storage amount, and reducing inlet and outlet NO according to selective catalyst_XAnd calculating the exhaust flow to obtain a basic ammonia injection amount, and adding the ammonia injection correction amount and the basic ammonia injection amount to obtain an actual ammonia injection amount.

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