CN112240235B - SCR control method and device - Google Patents

SCR control method and device Download PDF

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Publication number
CN112240235B
CN112240235B CN201910646118.4A CN201910646118A CN112240235B CN 112240235 B CN112240235 B CN 112240235B CN 201910646118 A CN201910646118 A CN 201910646118A CN 112240235 B CN112240235 B CN 112240235B
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scr
target scr
target
ammonia
nox
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CN112240235A (en
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曹璐
李栋
高祥
尚明
高波
张新宇
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SAIC Motor Corp Ltd
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SAIC Motor Corp Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • F01N9/005—Electrical control of exhaust gas treating apparatus using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Abstract

The embodiment of the application discloses a control method and a device of SCR, and the method comprises the following steps: first, the upstream NOx mass flow rate of the target SCR is acquired, then, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3, and the closed-loop correction coefficient corresponding to the target SCR are calculated, and then, determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR, it can be seen that the method does not directly perform closed-loop control processing after simply converting into required NH3 after acquiring the upstream NOx mass flow of the target SCR, but firstly utilizes the ammonia-nitrogen ratio, the NOx conversion efficiency and the storage or desorption rate of NH3 to process the upstream NOx mass flow, then utilizes the closed-loop correction coefficient to further process, so that the urea injection quantity can be more accurately determined and used for reacting ammonia and NOx, the NOx emission and ammonia leakage can meet the national VI emission regulation of the heavy-duty diesel engine.

Description

SCR control method and device
Technical Field
The present disclosure relates to the field of engine technology, and more particularly, to a method and an apparatus for controlling a Selective Catalytic Reduction (SCR) system.
Background
With the rapid development of economy and the acceleration of urbanization speed, the utilization rate of automobiles is higher and higher, but the defects of the automobiles are gradually shown while the automobiles provide quick travel conditions for people. Among them, exhaust emission is a very important problem, which seriously affects the health of people. Therefore, there is a need to enhance the control of engine NOx emissions.
At present, the SCR system in an aftertreatment system is mostly adopted to control the emission amount of NOx gas, and the principle is to inject urea into exhaust gas discharged by an engine, decompose the urea to generate ammonia, and react the ammonia and NOx under the action of a catalyst so as to reduce the emission of NOx. The SCR control strategy mainly comprises an open-loop control strategy and a closed-loop control strategy, but the current open-loop SCR control strategy cannot meet the strict requirements of national VI emission regulations, because the current open-loop SCR control strategy cannot judge the accuracy and the precision of the calculated urea injection amount, the finally calculated urea injection amount can be deviated due to the deviation of the post-treatment ammonia storage amount, the change of the urea concentration and the like, and the downstream NOx emission in an SCR system is higher or the ammonia leakage is higher. In addition, although a conventional SCR closed-loop control strategy can form a closed-loop control system based on a downstream NOx sensor, on one hand, an open-loop deviation caused by the reduction of the NOx treatment capacity of an aftertreatment component cannot be overcome due to the open-loop control based on pulse spectrums, and on the other hand, the urea injection amount cannot be accurately controlled due to the cross sensitivity of the NOx sensor to NOx and NH3 during closed-loop feedback, so that the downstream NOx emission in the SCR system is higher or the ammonia slip is higher.
Therefore, how to utilize a more advanced method to realize the accurate control of the SCR, namely the accurate control of the urea injection amount in the SCR, so as to meet the NOx emission requirement of the diesel engine in VI of the heavy country and ensure that the ammonia leakage amount does not exceed the standard, becomes a problem to be solved urgently.
Disclosure of Invention
In view of this, the embodiment of the present application provides a method and a device for controlling an SCR, so as to solve the technical problem that the prior art cannot accurately calculate the urea injection amount of the SCR, and thus cannot meet the NOx emission requirement and the ammonia leakage emission standard of the diesel engine vi in heavy countries.
In order to solve the above problem, the technical solution provided by the embodiment of the present application is as follows:
in a first aspect, the present application provides a method for controlling an SCR, the method comprising:
acquiring the upstream NOx mass flow of a target SCR;
calculating the ammonia nitrogen ratio corresponding to the target SCR;
calculating the NOx conversion efficiency corresponding to the target SCR;
calculating the storage or desorption rate of NH3 corresponding to the target SCR;
calculating a closed loop correction coefficient corresponding to the target SCR;
and determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR.
In an optional implementation manner, the calculating an ammonia nitrogen ratio corresponding to the target SCR includes:
and calibrating a pulse spectrum according to the ammonia nitrogen ratio coefficient, and calculating the ammonia nitrogen ratio corresponding to the target SCR.
In an alternative implementation, the calculating the NOx conversion efficiency corresponding to the target SCR includes:
and calibrating a pulse spectrum according to the NOx conversion efficiency, and calculating the NOx conversion efficiency corresponding to the target SCR.
In an alternative implementation, the determining the urea injection amount of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3, and the closed-loop correction coefficient of the target SCR includes:
performing product calculation on the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR to obtain a first product result;
performing product calculation on the first product result and the NOx conversion efficiency corresponding to the target SCR to obtain a second product result;
adding the second product result to the storage or desorption rate corresponding to the target SCR to obtain the feedforward open-loop ammonia demand quality corresponding to the target SCR;
performing product calculation on the feedforward open-loop ammonia required mass flow corresponding to the target SCR and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result;
and multiplying the third product result by a preset proportional coefficient of the mass of the urea solution with the urea concentration of 32.5% and the mass of ammonia to obtain the urea injection amount of the target SCR.
In an alternative implementation, the predetermined urea concentration of 32.5% of the urea solution is 5.425.
In a second aspect, the present application provides a control device for an SCR, the device comprising:
an acquisition unit for acquiring an upstream NOx mass flow of a target SCR;
the first calculating unit is used for calculating the ammonia nitrogen ratio corresponding to the target SCR;
the second calculating unit is used for calculating the NOx conversion efficiency corresponding to the target SCR;
a third calculating unit, configured to calculate a storage or desorption rate of NH3 corresponding to the target SCR;
the fourth calculating unit is used for calculating a closed loop correction coefficient corresponding to the target SCR;
and the determining unit is used for determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR.
In an optional implementation manner, the first computing unit is specifically configured to:
and calibrating a pulse spectrum according to the ammonia nitrogen ratio coefficient, and calculating the ammonia nitrogen ratio corresponding to the target SCR.
In an optional implementation manner, the second computing unit is specifically configured to:
and calibrating a pulse spectrum according to the NOx conversion efficiency, and calculating the NOx conversion efficiency corresponding to the target SCR.
In an optional implementation manner, the determining unit includes:
the first product subunit is used for carrying out product calculation on the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR to obtain a first product result;
the second product subunit is used for carrying out product calculation on the first product result and the NOx conversion efficiency corresponding to the target SCR to obtain a second product result;
the addition subunit is configured to add the second product result to the storage or desorption rate corresponding to the target SCR to obtain a feed-forward open-loop ammonia demand quality corresponding to the target SCR;
the third product sub-unit is used for calculating the product of the feedforward open-loop ammonia required mass flow corresponding to the target SCR and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result;
and the fourth product subunit is used for multiplying the third product result by a preset proportional coefficient of the urea solution with the urea concentration of 32.5% and the ammonia mass to obtain the urea injection amount of the target SCR.
In an alternative implementation, the predetermined urea concentration of 32.5% of the urea solution is 5.425.
Therefore, the embodiment of the application has the following beneficial effects:
in the embodiment of the application, the upstream NOx mass flow rate of the target SCR is firstly obtained, then the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient corresponding to the target SCR are calculated, and then the urea injection amount of the target SCR can be determined according to the upstream NOx mass flow rate, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR, so that in the embodiment of the application, after the upstream NOx mass flow rate of the target SCR is obtained, the closed-loop control processing is not simply converted into the required NH3 and then is directly performed, but the obtained upstream NOx mass flow rate is processed by using the calculated ammonia-nitrogen ratio, NOx conversion efficiency and the storage or desorption rate of NH3, and then is further processed by using the closed-loop correction coefficient, so that a more accurate urea injection amount can be obtained and used for reacting ammonia and NOx, the NOx emission and ammonia leakage can meet the national VI emission regulation of the heavy-duty diesel engine.
Drawings
FIG. 1 is a functional block diagram of a conventional SCR closed-loop control strategy;
fig. 2 is a flowchart of a control method of an SCR according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram of a calibration pulse spectrum of an ammonia nitrogen ratio coefficient provided in the embodiment of the present application;
FIG. 4 is a graphical illustration of a calibration pulse spectrum of NOx conversion efficiency provided by an embodiment of the present application;
fig. 5 is a block diagram of a structure for calculating a storage or desorption rate of NH3 corresponding to a target SCR according to an embodiment of the present application;
fig. 6 is a schematic overall structure diagram of a control method of an SCR according to an embodiment of the present disclosure;
FIG. 7 is a graphical representation of downstream NOx emissions from a WHTC cycle provided by an embodiment of the present application;
FIG. 8 is a schematic diagram illustrating NH3 leakage during a WHTC cycle according to an embodiment of the present disclosure;
fig. 9 is a schematic structural diagram of a control device of an SCR according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
In order to facilitate understanding of the technical solutions provided in the present application, the following briefly describes the research background of the technical solutions in the present application.
In order to adapt to the rapid development of society, vehicles powered by internal combustion engines, such as automobiles, are widely used. However, the disadvantages of these vehicles are gradually revealed while they provide people with quick travel conditions. Among them, exhaust emission is a very important problem, which seriously affects the health of people. Therefore, there is a need to enhance the control of engine NOx emissions.
At present, the SCR system in an aftertreatment system is mostly adopted to control the emission amount of NOx gas, in the SCR technology, the control of urea injection amount is a key technology, if the urea injection amount is too small, NOx cannot be effectively reduced into N2 (nitrogen) and water through reaction, and the residual NOx is too much; if the urea injection amount is too large, more residual NH3 will be created, causing NH3 to slip very high.
Specifically, the current SCR control strategies are mainly classified into two types, an open-loop control strategy and a closed-loop control strategy, wherein the current SCR open-loop control strategies are classified into a pulse spectrum-based control strategy and a model-based control strategy. The open-loop control strategy based on pulse spectrum firstly determines the initial injection pulse spectrum according to the NOx concentration, the internal temperature of a catalytic converter and the like under different engine working conditions, and finally adds a plurality of control strategies for correcting the pulse spectrum according to transient change. The open-loop control strategy based on the model is to form an initial controllable pulse spectrum by establishing the model and the like and perform transient correction on the basis.
Although the open-loop SCR control scheme enables fast reaction according to the model, the urea injection amount is calculated quickly. However, in the face of stringent emissions legislation in country vi, current open-loop SCR control strategies have not been able to meet the requirements because current open-loop control strategies are unable to make a determination as to the accuracy and precision of the calculated urea injection quantity. Further, deviation of the post-treatment ammonia storage amount, change of the urea concentration and the like can cause deviation of the finally calculated urea injection amount, so that downstream NOx emission in the SCR system is high or ammonia leakage is high.
While the conventional SCR closed-loop control strategy shown in fig. 1 is generally based on a pulse spectrum open loop and adds a downstream NOx sensor to perform closed-loop PI feedback control, although this control method can form a closed-loop control system based on the downstream NOx sensor, on one hand, the open-loop control based on the pulse spectrum cannot overcome the open-loop deviation caused by the decrease of the NOx treatment capability of the aftertreatment component, and on the other hand, the urea injection amount cannot be accurately controlled due to the cross-sensitivity of the NOx sensor to NOx and NH3 during closed-loop feedback, which may cause the downstream NOx emission to be high or the ammonia slip to be ultra-high in the SCR system.
Based on the method and the device, the urea injection amount of the target SCR can be accurately controlled, the NOx emission requirement of the heavy country VI diesel engine can be met, and the ammonia leakage amount is not over-standard.
Next, the method will be described in detail with reference to the accompanying drawings.
Referring to fig. 2, which shows a flowchart of a control method of an SCR according to an embodiment of the present application, as shown in fig. 2, the method includes:
s201: an upstream NOx mass flow of the target SCR is obtained.
In the embodiment of the present application, an SCR that needs to be accurately controlled is defined as a target SCR, and a vehicle to which the target SCR belongs is defined as a target vehicle. In order to realize accurate control of the urea injection amount of the target SCR, the feedforward NOx open-loop control strategy corresponding to the target SCR may be realized by executing steps S201 to S204 to obtain the feedforward open-loop ammonia required mass flow corresponding to the target SCR, so as to accurately calculate the accurate urea injection amount of the target SCR through subsequent steps S205 to S206.
Specifically, in step S201, the upstream NOx mass flow rate of the target SCR can be calculated by an upstream NOx source emission model (in mg/S) preset in an upstream NOx sensor of the target SCR system according to the volume concentration (in ppm) output by the NOx sensor, the exhaust gas mass flow rate, and the humidity correction coefficient, and the specific calculation formula is as follows:
NOXmass＝0.001587×NOXconc×KH,D×GEXHW (1)
wherein NOXmassRepresents the upstream NOx mass flow of the target SCR in g/s; NOXconcRepresents the direct sampling volume concentration of NOx output by a NOx sensor upstream of the target SCR in ppm; kH,DA humidity correction coefficient representing a target SCR intake air; gEXHWThe mass flow of the exhaust gas is expressed in kg/s.
S202: and calculating the ammonia nitrogen ratio corresponding to the target SCR.
In this embodiment, in order to accurately control the urea injection amount of the target SCR, after the upstream NOx mass flow rate of the target SCR is obtained in step S201, the ammonia nitrogen ratio corresponding to the target SCR needs to be calculated, wherein the ammonia nitrogen ratio refers to the ratio of the consumption amount of NH3 to the mass of NOx actually participating in the reaction under a certain condition.
Specifically, an optional implementation manner is that a pulse spectrum can be calibrated according to the ammonia nitrogen ratio coefficient, and the ammonia nitrogen ratio corresponding to the target SCR is calculated.
In this implementation, as shown in fig. 3, it shows the ammonia nitrogen ratio coefficient calibration pulse spectrum provided in the embodiment of the present application, as shown in fig. 3, wherein the x-axis represents NO2The y-axis represents the average carrier temperature of the target SCR, and in the process of calculating the ammonia nitrogen ratio corresponding to the target SCR, the calibration operation can be completed by continuously adjusting the ammonia nitrogen ratio coefficient until the calibrated SCR conversion efficiency is equal to the real NOx conversion efficiency, so that the ammonia nitrogen ratio corresponding to the target SCR is obtained.
S203: and calculating the NOx conversion efficiency corresponding to the target SCR.
In this embodiment, in order to accurately control the urea injection amount of the target SCR, the NOx conversion efficiency corresponding to the target SCR needs to be calculated, and the specific calculation formula is as follows:
SCReat＝1-SCR downstream NOxVolume concentration/SCR upstream NOxVolume concentration (2)
Wherein, SCReatIndicating the NOx conversion efficiency corresponding to the target SCR.
Specifically, an alternative implementation may calibrate the pulse spectrum for the NOx conversion efficiency corresponding to the target SCR.
In this implementation, the NOx emission amount may be measured upstream and downstream of the target SCR, thereby calculating the NOx conversion efficiency corresponding to the target SCR. As shown in fig. 4, which shows a NOx conversion efficiency calibration pulse spectrum provided in the embodiment of the present application, as shown in fig. 4, where the x axis represents the exhaust gas flow rate, and the y axis represents the average carrier temperature of the target SCR, in the process of calculating the NOx conversion efficiency corresponding to the target SCR, the actual NOx conversion efficiency can be calculated by using the above formula (2) and the upstream and downstream NOx emissions of the target SCR, and is output to the NOx efficiency pulse spectrum, and the final NOx conversion efficiency corresponding to the target SCR is obtained by continuously adjusting the NOx conversion efficiency.
S204: and calculating the storage or desorption rate of NH3 corresponding to the target SCR.
In the embodiment, in order to realize accurate control of the urea injection amount of the target SCR, the storage or desorption rate of NH3 corresponding to the target SCR needs to be calculated, wherein the storage of NH3 refers to the capability of the target SCR carrier to store NH3 under different exhaust gas flow rates and target SCR temperatures.
Specifically, as shown in fig. 5, a structural block diagram is shown for calculating a storage or desorption rate of NH3 corresponding to a target SCR provided in the embodiment of the present application, where mNH3LdNom represents a real storage amount of NH3 in the target SCR, and a unit may be g, mes NH3Ld represents a storage amount of NH3 obtained by performing integral calculation step by step through software, and a unit may also be g, SCRLdG _ tish 3LdGov _ CUR represents a time (or a time speed) for storing or desorbing NH3 corresponding to the target SCR, and a unit may be s, and then a storage or desorption rate calculation process of NH3 corresponding to the target SCR is as follows: the actual storage amount mNH3LdNom of NH3 in the target SCR is first subtracted by the difference result obtained by subtracting the NH3 storage amount msetnh 3Ld estimated by software stepwise integration, and then the difference result is divided by the storage or desorption time SCRLdG _ tiNH3LdGov _ CUR of NH3 corresponding to the target SCR, so that the storage or desorption rate of NH3 corresponding to the target SCR can be obtained and can be defined as SCRLdG _ dmNH3LdGov _ mp, as shown in fig. 5.
S205: and calculating a closed loop correction coefficient corresponding to the target SCR.
In this embodiment, in order to accurately control the urea injection amount of the target SCR, it is also necessary to calculate a closed-loop correction coefficient corresponding to the target SCR. Specifically, feedback control may be performed by PI, and a deviation value between the calculated downstream NOx estimated value and the actual value of NOx detected by the downstream NOx sensor may be obtained by comparing the estimated value with the actual value according to the operating principle of the PI regulator, and a deviation coefficient may be generated based on the deviation value, and then a proportional constant and an integral constant may be generated based on the carrier temperature and the exhaust gas flow rate of the target SC R to output a PI correction coefficient for correcting the downstream NOx.
It should be noted that the specific process of calculating the closed-loop correction coefficient corresponding to the target SCR in step S205 is the same as that of the conventional method, and is not described herein again.
S206: and determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR.
In practical applications, after the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, and the storage or desorption rate of NH3 of the target SCR are obtained through the above steps S201 to S204, the feedforward NOx open-loop control strategy corresponding to the target SCR can be implemented by using these data, so as to obtain the feedforward open-loop ammonia required mass flow corresponding to the target SCR. Then, the feedforward open-loop ammonia required mass flow and the closed-loop correction coefficient corresponding to the target SCR calculated in step S205 are further processed to accurately determine the urea injection amount of the target SCR.
Specifically, in an alternative implementation manner, the implementation process of step S206 may specifically include the following steps a to E:
and step A, performing product calculation on the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR to obtain a first product result.
In the implementation mode, in order to accurately determine the urea injection amount of the target SCR, firstly, the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR are multiplied to obtain a first product result, and the first product result refers to the ammonia mass flow required by complete reaction.
And B, performing product calculation on the first product result and the NOx conversion efficiency corresponding to the target SCR to obtain a second product result.
After the first product result (i.e. the required ammonia mass flow rate during complete reaction) is obtained in step a, the first product result may be multiplied by the NOx conversion efficiency corresponding to the target SCR to obtain a second product result, which is referred to as the actually required ammonia mass flow rate.
And C, adding the second product result to the storage or desorption rate corresponding to the target SCR to obtain the feedforward open-loop ammonia demand quality corresponding to the target SCR.
After the second product result (i.e. the actually required ammonia mass flow) is obtained in step B, the second product result may be added to the storage or desorption rate corresponding to the target SCR to eliminate the dynamic ammonia flow deviation, so as to obtain the feedforward open-loop ammonia demand quality corresponding to the target SCR.
And D, performing product calculation on the mass flow required by the feedforward open-loop ammonia corresponding to the target SCR and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result.
After the feedforward open-loop ammonia demand quality corresponding to the target SCR is obtained through step C, further, product calculation may be performed on the feedforward open-loop ammonia demand and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result.
And E, multiplying the third product result by a preset proportional coefficient of the urea solution with the urea concentration of 32.5% and the ammonia mass to obtain the urea injection quantity of the target SCR.
After the third product result is obtained in step D, the third product result may be further multiplied by a predetermined proportionality coefficient between the urea solution with the urea concentration of 32.5% and the ammonia mass to obtain the urea injection amount of the target SCR, wherein, in an alternative implementation manner, the proportionality coefficient between the urea solution with the urea concentration of 32.5% and the ammonia mass may be 5.425.
Therefore, the embodiment of the application not only realizes the feedforward NOx open-loop control strategy corresponding to the target SCR by executing the steps S201-S204 to accurately control the urea injection amount under the working condition of the steady-state engine, but also adds the storage characteristics of the target SCR under different temperature and airspeed conditions in the dynamic process into the ammonia storage amount calculation process, thereby accurately controlling the urea injection amount required by the transient process. For the problems of deviation, reduction of aftertreatment efficiency and the like in open-loop control, the aim of effectively and accurately controlling the downstream NOx and ammonia leakage amount of the target SCR can be achieved through subsequent closed-loop control.
In summary, the SCR control method according to the embodiment of the present application first obtains the upstream NOx mass flow rate of the target SCR, then calculates the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3, and the closed-loop correction coefficient corresponding to the target SCR, and then determines the urea injection amount of the target SCR according to the upstream NOx mass flow rate, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3, and the closed-loop correction coefficient of the target SCR, so that the embodiment of the present application does not directly perform the closed-loop control processing after simply converting into the required NH3 after obtaining the upstream NOx mass flow rate of the target SCR, but performs the processing on the obtained upstream NOx mass flow rate by using the calculated ammonia-nitrogen ratio, NOx conversion efficiency, and storage or desorption rate of NH3 of the target SCR, and then performs the further processing by using the closed-loop correction coefficient, thereby obtaining a more accurate urea injection amount, and the reaction of ammonia and NOx is carried out, so that the NOx emission and ammonia leakage can meet the national VI emission regulation of heavy-duty diesel engines.
For ease of understanding, reference is now made to the overall schematic diagram of a control method for an SCR as shown in fig. 6. The implementation process of the SCR control method provided in the embodiment of the present application is described.
As shown in fig. 6, the implementation process of the embodiment of the present application is as follows: firstly, acquiring an upstream NOx mass flow rate of a target SCR through an upstream NOx source emission model preset in an upstream NOx sensor of a target SCR system, then, performing product calculation on the upstream NOx mass flow rate and an ammonia nitrogen ratio corresponding to the target SCR to obtain an ammonia mass flow rate required by complete reaction, then, performing product calculation on the ammonia mass flow rate required by the complete reaction and NOx conversion efficiency corresponding to the target SCR to obtain an actually required ammonia mass flow rate, then, adding the actually required ammonia mass flow rate to a storage or desorption rate corresponding to the target SCR to eliminate dynamic ammonia flow rate deviation to obtain a feedforward open-loop ammonia required quality corresponding to the target SCR, further, performing product calculation on the feedforward open-loop ammonia required quality and a closed-loop correction coefficient corresponding to the target SCR, and multiplying the obtained product result by a preset proportional coefficient of urea solution with the urea concentration of 32.5% and the ammonia mass, and obtaining the urea injection quantity of the target SCR, wherein the concrete implementation process is shown in steps S201-S206.
Next, by way of example, an application process of the SCR control method provided in the embodiment of the present application will be described with reference to fig. 7 and 8.
For example, the following steps are carried out: taking a certain 2.0L heavy national VI diesel engine as an example, the rated power of the engine is 102kw @3500rpm, the maximum torque is 330Nm, and the WHTC cycle power is 8.92kwh, the method is applied to the diesel engine, firstly, NOx sensors are arranged on the upstream and the downstream of the SCR (NOx source is discharged from the sensors and does not need to be calibrated independently), then, the ammonia-nitrogen ratio and the NOx conversion efficiency of the engine under different working conditions and under different temperature and airspeed conditions are calibrated, then, the storage or desorption rate of NH3 under different temperatures and exhaust gas flow rates is calibrated according to the ammonia storage characteristic of a post-treatment carrier, further, the fac correction coefficient, the proportion and the time constant under different SCR temperatures and exhaust gas flow rates are calibrated according to the upstream and downstream NOx deviation, further, the closed-loop correction coefficient can be obtained, finally, the calibrated WHTC cycle downstream NOx emission and NH3 leakage can be obtained, wherein the finally obtained schematic diagram of the calibrated WHTC cycle downstream NOx emission is shown in FIG. 7, and a resulting plot of NH3 slip in the calibrated WHTC cycle are shown in fig. 8.
Referring to fig. 7, after the control method of the SCR described above, it can be obtained that the estimated emission amount of NOx in the engine post-treatment is 4.7g/h, and since the WHTC cycle work is 8.92kwh, the emission amount of NOx can be obtained by calculation as follows: 4.7 × 1800/3600/8.92 ═ 0.263g/kwh, which is lower than 0.46g/kwh required by the national VI regulation, namely, the national VI regulation requirement is met.
Referring to fig. 8, after the control method of the SCR is used, the average value of NH3 leakage in the engine aftertreatment is 5ppm, which is lower than the 10ppm limit required by the national vi regulation, that is, the requirement of the national vi regulation is met.
The foregoing embodiments describe the technical solutions of the methods of the present application in detail, and accordingly, the present application further provides a control device of an SCR, which is described below.
Referring to fig. 9, fig. 9 is a structural diagram of a control device of an SCR according to an embodiment of the present application, and as shown in fig. 9, the control device includes:
an obtaining unit 901 for obtaining an upstream NOx mass flow of a target SCR;
a first calculating unit 902, configured to calculate an ammonia nitrogen ratio corresponding to the target SCR;
a second calculating unit 903, configured to calculate a NOx conversion efficiency corresponding to the target SCR;
a third calculating unit 904, configured to calculate a storage or desorption rate of NH3 corresponding to the target SCR;
a fourth calculating unit 905, configured to calculate a closed-loop correction coefficient corresponding to the target SCR;
a determination unit 906 for determining a urea injection amount of the target SCR according to an upstream NOx mass flow rate, an ammonia-nitrogen ratio, a NOx conversion efficiency, a storage or desorption rate of NH3, and a closed-loop correction coefficient of the target SCR.
Optionally, the first calculating unit 902 is specifically configured to:
and calibrating a pulse spectrum according to the ammonia nitrogen ratio coefficient, and calculating the ammonia nitrogen ratio corresponding to the target SCR.
Optionally, the second calculating unit 903 is specifically configured to:
and calibrating a pulse spectrum according to the NOx conversion efficiency, and calculating the NOx conversion efficiency corresponding to the target SCR.
Optionally, the determining unit 906 includes:
the first product subunit is used for carrying out product calculation on the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR to obtain a first product result;
the second product subunit is used for carrying out product calculation on the first product result and the NOx conversion efficiency corresponding to the target SCR to obtain a second product result;
the addition subunit is configured to add the second product result to the storage or desorption rate corresponding to the target SCR to obtain a feed-forward open-loop ammonia demand quality corresponding to the target SCR;
the third product sub-unit is used for calculating the product of the feedforward open-loop ammonia required mass flow corresponding to the target SCR and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result;
and the fourth product subunit is used for multiplying the third product result by a preset proportional coefficient of the urea solution with the urea concentration of 32.5% and the ammonia mass to obtain the urea injection amount of the target SCR.
Optionally, the predetermined urea concentration is 32.5% of urea solution and the ratio coefficient of ammonia mass is 5.425.
In this way, the SCR control apparatus according to the embodiment of the present application first obtains the upstream NOx mass flow rate of the target SCR, then calculates the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3, and the closed-loop correction coefficient corresponding to the target SCR, and then determines the urea injection amount of the target SCR according to the upstream NOx mass flow rate, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3, and the closed-loop correction coefficient of the target SCR, and thus, the embodiment of the present application does not perform the closed-loop control process directly after simply converting the upstream NOx mass flow rate into the required NH3 after obtaining the upstream NOx mass flow rate of the target SCR, but performs the processing on the obtained upstream NOx mass flow rate by using the calculated ammonia-nitrogen ratio, NOx conversion efficiency, and storage or desorption rate of NH3, and then performs the further processing by using the closed-loop correction coefficient, thereby obtaining a more accurate urea injection amount, and the reaction of ammonia and NOx is carried out, so that the NOx emission and ammonia leakage can meet the national VI emission regulation of heavy-duty diesel engines.
It should be noted that, in the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other. For the system or the device disclosed by the embodiment, the description is simple because the system or the device corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (8)

1. A method of controlling an SCR, the method comprising:
acquiring the upstream NOx mass flow of a target SCR;
calculating the ammonia nitrogen ratio corresponding to the target SCR;
calculating the NOx conversion efficiency corresponding to the target SCR;
calculating the storage or desorption rate of NH3 corresponding to the target SCR;
calculating a closed loop correction coefficient corresponding to the target SCR;
determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and a closed-loop correction coefficient of the target SCR;
the determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia-nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR comprises the following steps: performing product calculation on the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR to obtain a first product result; performing product calculation on the first product result and the NOx conversion efficiency corresponding to the target SCR to obtain a second product result; adding the second product result to the storage or desorption rate corresponding to the target SCR to obtain the feedforward open-loop ammonia demand quality corresponding to the target SCR; performing product calculation on the feedforward open-loop ammonia required mass flow corresponding to the target SCR and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result; and multiplying the third product result by a preset proportional coefficient of the mass of the urea solution with the urea concentration of 32.5% and the mass of ammonia to obtain the urea injection amount of the target SCR.
2. The method according to claim 1, wherein the calculating the ammonia nitrogen ratio corresponding to the target SCR comprises:
and calibrating a pulse spectrum according to the ammonia nitrogen ratio coefficient, and calculating the ammonia nitrogen ratio corresponding to the target SCR.
3. The method of claim 1, wherein said calculating a corresponding NOx conversion efficiency for the target SCR comprises:
and calibrating a pulse spectrum according to the NOx conversion efficiency, and calculating the NOx conversion efficiency corresponding to the target SCR.
4. The method according to claim 1, wherein the predetermined urea concentration is 32.5% by mass of urea solution to ammonia with a proportionality coefficient of 5.425.
5. A control device for an SCR, the device comprising:
an acquisition unit for acquiring an upstream NOx mass flow of a target SCR;
the first calculating unit is used for calculating the ammonia nitrogen ratio corresponding to the target SCR;
the second calculating unit is used for calculating the NOx conversion efficiency corresponding to the target SCR;
a third calculating unit, configured to calculate a storage or desorption rate of NH3 corresponding to the target SCR;
the fourth calculating unit is used for calculating a closed loop correction coefficient corresponding to the target SCR;
a determining unit, which is used for determining the urea injection quantity of the target SCR according to the upstream NOx mass flow, the ammonia nitrogen ratio, the NOx conversion efficiency, the storage or desorption rate of NH3 and the closed-loop correction coefficient of the target SCR;
the determination unit includes: the first product subunit is used for carrying out product calculation on the upstream NOx mass flow of the target SCR and the ammonia nitrogen ratio corresponding to the target SCR to obtain a first product result; the second product subunit is used for carrying out product calculation on the first product result and the NOx conversion efficiency corresponding to the target SCR to obtain a second product result; the addition subunit is configured to add the second product result to the storage or desorption rate corresponding to the target SCR to obtain a feed-forward open-loop ammonia demand quality corresponding to the target SCR; the third product sub-unit is used for calculating the product of the feedforward open-loop ammonia required mass flow corresponding to the target SCR and the closed-loop correction coefficient corresponding to the target SCR to obtain a third product result; and the fourth product subunit is used for multiplying the third product result by a preset proportional coefficient of the urea solution with the urea concentration of 32.5% and the ammonia mass to obtain the urea injection amount of the target SCR.
6. The apparatus according to claim 5, wherein the first computing unit is specifically configured to:
and calibrating a pulse spectrum according to the ammonia nitrogen ratio coefficient, and calculating the ammonia nitrogen ratio corresponding to the target SCR.
7. The apparatus according to claim 5, wherein the second computing unit is specifically configured to:
and calibrating a pulse spectrum according to the NOx conversion efficiency, and calculating the NOx conversion efficiency corresponding to the target SCR.
8. The apparatus according to claim 5, wherein the predetermined urea concentration is a ratio of 32.5% urea solution to ammonia mass of 5.425.
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