CN117189326A - Real-time estimation method for ammonia leakage quantity of rear end of SCR (selective catalytic reduction) of diesel engine - Google Patents
Real-time estimation method for ammonia leakage quantity of rear end of SCR (selective catalytic reduction) of diesel engine Download PDFInfo
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- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims abstract description 636
- 229910021529 ammonia Inorganic materials 0.000 title claims abstract description 313
- 238000000034 method Methods 0.000 title claims abstract description 58
- 238000010531 catalytic reduction reaction Methods 0.000 title description 2
- 239000003054 catalyst Substances 0.000 claims abstract description 136
- 238000004364 calculation method Methods 0.000 claims abstract description 73
- 238000012937 correction Methods 0.000 claims abstract description 34
- 230000001052 transient effect Effects 0.000 claims abstract description 28
- 238000005259 measurement Methods 0.000 claims description 43
- 230000008859 change Effects 0.000 claims description 12
- 230000032683 aging Effects 0.000 claims description 9
- 238000005070 sampling Methods 0.000 claims description 8
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 abstract description 16
- 239000004202 carbamide Substances 0.000 abstract description 16
- 238000002347 injection Methods 0.000 abstract description 12
- 239000007924 injection Substances 0.000 abstract description 12
- 238000005457 optimization Methods 0.000 abstract description 4
- 238000006243 chemical reaction Methods 0.000 description 12
- 230000035945 sensitivity Effects 0.000 description 11
- 230000008569 process Effects 0.000 description 9
- 230000000875 corresponding effect Effects 0.000 description 5
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 239000003638 chemical reducing agent Substances 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000002596 correlated effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
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- 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 application relates to an embodiment, the method for calculating the ammonia leakage amount under the steady-state working condition comprises the following steps: when the actual ammonia storage amount in the SCR catalyst exceeds the maximum ammonia storage amount of the SCR catalyst, calculating a first ammonia slip amount according to the actual ammonia storage amount in the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst; calculating a second ammonia slip from the ammonia coverage of the SCR catalyst when the ammonia coverage of the SCR catalyst exceeds a limit; and calculating the ammonia leakage amount under the steady-state working condition according to the first ammonia leakage amount and the second ammonia leakage amount. Through the calculation of the ammonia leakage amount based on the steady-state working condition, the calculation of the ammonia leakage amount based on the transient working condition and the correction of the ammonia leakage amount based on the rear NOx sensor, NH is improved after accurate calibration and optimization 3 Calculation accuracy of leakage amount, NH is realized 3 The real-time estimation of the leakage quantity ensures the closed-loop correction control of the SCR ammonia storage control, and realizes the accurate control of the urea injection quantity, thereby reaching the expected emission result.
Description
Technical Field
The application relates to the field of engine tail gas purification treatment control, in particular to a real-time estimation method for ammonia leakage quantity at the rear end of a diesel engine SCR.
Background
Currently, urea-SCR technology is applied to heavy diesel engines in a large scale. The reductant employed by the SCR system is urea. Urea is decomposed into NH at high temperature after being added with water 3 And CO 2 The working principle is that a reducing agent NH 3 Spraying into exhaust pipe, nitrogen oxide and NH in the exhaust 3 The reaction is reduced into nitrogen and water, thereby achieving the aim of reducing the harmful component NOx in the emission of the diesel engine. In order to pursue high NOx conversion efficiency of diesel aftertreatment SCR systems, urea is generally injected in excess; excessive urea injection can cause post-treatment NH emissions 3 And the leakage amount exceeds the standard, urea is wasted, and the EGP urea is crystallized after the post-treatment. SCR System will NH 3 As reducing agent, also often accompanied by NH at the outlet of the exhaust gas 3 Has NH before and after catalyst of the whole SCR system 3 Is present. Thus, there is a great error in the measurement of the concentration of NOx. If the NOx sensor factor pair NH is ignored 3 Measurement errors due to cross sensitivity will have a significant impact on the subsequent accurate control of the SCR system. To solve the adverse effect of the excessive injection of the urea injection quantity, the urea injection needs to be liftedThe accuracy of the control requires accurate real-time estimation of the ammonia leakage. Based on the ammonia leakage amount estimated in real time, the urea injection amount is adjusted and optimized in real time, and finally the high NOx conversion efficiency and low NH of the diesel engine aftertreatment SCR system are realized 3 Leakage amount.
In the related art, an ammonia leakage amount calculation method of an SCR aftertreatment system is disclosed. In the method, a relation between a current downstream NOx sensor measurement value and the ammonia leakage amount and a relation between a 1s front downstream NOx sensor measurement value and the ammonia leakage amount are obtained; the current ammonia leakage amount is calculated on the basis, and the ammonia leakage amount calculation value is processed through low-pass filtering. In addition, correcting the calculated value of the ammonia leakage amount according to the variation trend of the calculated value of the ammonia leakage amount and the actual value of the ammonia leakage amount; when the NOx conversion efficiency obtained by the upstream NOx sensor measurement value and the downstream NOx sensor measurement value is greater than the threshold value, the ammonia slip amount calculation value is set to 0. In the related art, an accurate NH is also disclosed 3 The technical scheme provides a control method for accurately predicting NH 3 A method for controlling leakage amount. In the method, NH is accurately predicted according to the original NOx at the current moment, the final NOx at the current moment, the original NOx at the last moment, the final NOx at the last moment, the current conversion efficiency and the conversion efficiency at the last moment 3 Slip amount, NH to be predicted 3 The leakage is filtered. Accurate NH prediction by NOx sensor measurements using SCR system time lag characteristics 3 A method of leakage.
However, the above technical proposal satisfies the NH 3 Under the condition of leakage prediction, NH can be developed 3 Prediction of slip, NH thereof 3 The leakage amount prediction conditions were: original NOx, exhaust flow, DOC outlet temperature, SCR inlet temperature and SCR ammonia storage amount, all of which meet relevant measurement thresholds before starting to calculate NH 3 Leakage quantity prediction calculation, which cannot guarantee NH 3 The real-time estimation of the leakage quantity cannot ensure the closed-loop correction control of the SCR ammonia storage control, cannot realize the accurate control of the urea injection quantity, and cannot reach the expected valueAnd (5) discharging results.
Disclosure of Invention
The application provides a real-time estimation method for the ammonia leakage quantity at the rear end of a diesel engine SCR, which can solve the problems that the closed-loop correction control of the SCR ammonia storage control cannot be ensured, the accurate control of the urea injection quantity cannot be realized, and the expected emission result cannot be achieved in the related technology.
In a first aspect, an embodiment of the present application provides a method for estimating ammonia slip amount at a rear end of SCR of a diesel engine in real time, including: calculating the ammonia leakage amount under the steady-state working condition; calculating the ammonia leakage amount under the transient working condition according to the ammonia leakage amount under the steady-state working condition; according to the ammonia leakage amount and the post NO under the transient working condition X The measured value of the sensor corrects the ammonia leakage amount and improves NH 3 Calculation accuracy of leakage amount, NH is realized 3 And estimating the leakage quantity in real time.
With reference to the first aspect, in one embodiment, the method for calculating the ammonia leakage amount under the steady-state working condition includes: when the actual ammonia storage amount in the SCR catalyst exceeds the maximum ammonia storage amount of the SCR catalyst, calculating a first ammonia slip amount according to the actual ammonia storage amount in the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst; calculating a second ammonia slip from the ammonia coverage of the SCR catalyst when the ammonia coverage of the SCR catalyst exceeds a limit; and calculating the ammonia leakage amount under the steady-state working condition according to the first ammonia leakage amount and the second ammonia leakage amount. By integrating the actual ammonia storage amount inside the SCR catalyst, the maximum ammonia storage amount of the SCR catalyst, the ammonia coverage rate of the SCR catalyst and other factors in the calculation process, the NH is further improved 3 Calculation accuracy of leakage amount, NH 3 The real-time calculation of the leakage is more accurate.
With reference to the first aspect, in one implementation manner, the method for calculating the first ammonia leakage amount includes: based on NH storage within SCR catalyst 3 Initial value of quantity and store NH 3 Calculating the actual ammonia storage amount inside the SCR catalyst at a rate; calculating the maximum ammonia storage amount of the SCR catalyst according to the correction coefficient of the ammonia storage amount, which is in base with the SCR catalyst, of the working volume of the SCR catalyst and the aging of the SCR catalyst; according to the SCR catalystThe first ammonia slip is calculated from an actual ammonia storage amount inside the dosing agent and a maximum ammonia storage amount of the SCR catalyst.
With reference to the first aspect, in one implementation manner, the method for calculating the second ammonia leakage amount includes: calculating the ammonia coverage rate of the SCR catalyst according to the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst; the second ammonia slip is calculated as a function of ammonia coverage of the SCR catalyst.
With reference to the first aspect, in one embodiment, the method for calculating the ammonia leakage amount under the transient operating condition includes: and calculating the ammonia leakage amount under the transient working condition according to the ammonia leakage amount under the steady-state working condition, the ammonia leakage amount correction coefficient related to the catalyst temperature change rate and the sampling period. By integrating the factors such as ammonia leakage amount, ammonia leakage amount correction coefficient related to the catalyst temperature change rate, sampling period and the like in the calculation process, the NH is further improved 3 Calculation accuracy of leakage amount, NH 3 The real-time calculation of the leakage is more accurate.
With reference to the first aspect, in one embodiment, the method for correcting the ammonia leakage amount includes: according to the post NO X Sensor measurement versus true NH 3 And identifying and calculating the leakage quantity.
With reference to the first aspect, in an embodiment, the method is based on the post-NO X Sensor measurement versus true NH 3 The identification calculation of the leakage amount comprises the following steps: and when the measured value of the rear NOx sensor is smaller than a first threshold value, the measured value of the rear NOx sensor is the NOx concentration at the current moment.
With reference to the first aspect, in an embodiment, the method is based on the post-NO X Sensor measurement versus true NH 3 The identification calculation of the leakage amount comprises the following steps: and when the measured value of the rear NOx sensor is larger than a first threshold value, performing identification calculation according to the ammonia coverage rate level.
With reference to the first aspect, in one implementation, the performing the identification calculation according to the ammonia coverage level includes: and when the ammonia coverage rate is smaller than a second threshold value, the measured value of the rear NOx sensor is the NOx concentration at the current moment.
With reference to the first aspect, in one implementation, the performing the identification calculation according to the ammonia coverage level includes: when the ammonia coverage rate is greater than a second threshold value, the post NOx sensor measurement value is NH at the current time 3 A leakage value; calculating the real NH according to the ammonia leakage amount under the transient working condition, the measured value of the rear NOx sensor and the calculated weight correction coefficient 3 Leakage amount.
The method for accurately calculating the real-time estimation of the ammonia leakage quantity at the rear end of the SCR system comprises the following steps:
1. ammonia leakage calculation under steady-state working condition
The ammonia leakage under steady-state conditions is largely divided into two parts:
1) When the actual ammonia storage amount inside the SCR catalyst exceeds the SCR catalyst maximum ammonia storage amount, the ammonia slip amount is calculated at this time as:
m NH3_slip_base1 ＝m NH3_Store -m NH3_Capacity
m NH3_Capacity ＝m NH3_Capacity_base (T)×V SCR ×f SCR_aging
wherein:
m NH3Int for NH storage in calculated SCR catalyst 3 An initial value of the quantity;
for calculated NH storage 3 A rate;
m NH3_Capacity_base for maximum ammonia storage associated with SCR catalyst temperature, the maximum ammonia storage is mainly related to the characteristics of the carrier, the carrier temperature and the aging degree of the carrier;
V SCR a working volume for the SCR catalyst;
f SCR_aging and (5) correcting the coefficient for SCR catalyst aging.
2) Calculation of ammonia slip when the ammonia coverage of the SCR catalyst exceeds a limit
Only NH adsorbed on SCR catalyst 3 Can react with NOx in engine emission, and NH which is not adsorbed and desorbed 3 NH can occur 3 Escape, eventually causing ammonia leakage. SCR catalysts generally represent how much NH the SCR catalyst adsorbs by ammonia coverage 3 . When the ammonia coverage is high, the conversion efficiency of NOx is higher, but the higher the ammonia coverage increases the amount of ammonia slip.
m NH3_slip_base2 ＝f(θ NH3 )
By combining the above, the ammonia leakage amount in the steady state is calculated as:
m NH3_slip_Steady ＝m NH3_slip_base1 +m NH3_slip_base2
2. ammonia leakage amount calculation under transient working condition
The ammonia leakage change under the transient working condition is mainly related to the temperature of the SCR catalyst, and the more the temperature change of the SCR catalyst is, the more the ammonia leakage amount is, and the ammonia leakage amount under the transient working condition is:
m NH3_slip ＝{m NH3_slip_Steady (t)+m NH3_slip_Steady (t-1)×[1-f NH3_slip (t-1)]}×f NH3_slip (t)
where t is the sampling period, f NH3_slip The ammonia slip correction factor is correlated to the catalyst temperature change rate.
3. Ammonia leakage correction based on post-NOx sensor
In view of the ammonia slip amount calculation error, the NOx sensor measurement value after introduction needs to be corrected to ensure the accuracy of the final calculated ammonia slip amount. Taking into account NH of the rear NOx sensor 3 Measuring cross sensitivity requires measuring the post NOx sensor measurementsTrue NH of the reaction 3 And performing identification calculation.
a) When the post NOx sensor measurement is less than the threshold, then NOx and NH 3 The emission amount of the catalyst is low, the SCR is in a stage of just complete reaction, and the measured value of the rear NOx is considered to be the concentration of the NOx at the current moment;
b) When the post NOx sensor measurement is above a certain threshold and the ammonia coverage level is low, then the SCR is still capable of ammonia storage, NH 3 Less NH escapes 3 The cross sensitivity of the NOx sensor is less affected, and the measured value of the NOx sensor is considered to be the concentration of NOx at the current moment;
c) When the measured value of the rear NOx sensor is larger than the threshold value and the ammonia coverage rate is larger than the threshold value, the internal ammonia storage capacity of the SCR reaches the upper limit, NH 3 A large amount of slip, NOx, will be substantially fully reacted, at which point the NOx sensor measurement is considered to be substantially NH 3 Leakage amount, measured NH 3 Leakage value. Based on the post-NOx sensor measurements obtained from the test at this time, for an estimated NH 3 The leakage amount is corrected.
m NH3_slip_final ＝m NH3_slip +k×(NO X_measure -m NH3_slip )
The related sensor, the ammonia coverage rate threshold and the calculated weight correction coefficient K are obtained through qualitative adjustment and setting summary of multiple times of simulation tests and experiments.
The technical scheme provided by the embodiment of the application has the beneficial effects that at least:
through the calculation of the ammonia leakage amount based on the steady-state working condition, the calculation of the ammonia leakage amount based on the transient working condition and the correction of the ammonia leakage amount based on the rear NOX sensor, NH is improved after accurate calibration and optimization 3 Calculation accuracy of leakage amount, NH is realized 3 The real-time estimation of the leakage quantity ensures the closed-loop correction control of the SCR ammonia storage control, and realizes the accurate control of the urea injection quantity, thereby reaching the expected emission result.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for real-time estimation of ammonia slip on the rear end of a diesel SCR according to an embodiment of the present application;
FIG. 2 is a flow chart of the ammonia slip amount calculation based on the steady-state working condition in the method for estimating the ammonia slip amount at the rear end of the SCR of the diesel engine in real time according to the embodiment of the application;
FIG. 3 is a flow chart of the ammonia slip amount calculation based on transient conditions in the method for estimating the ammonia slip amount at the rear end of the SCR of the diesel engine in real time according to the embodiment of the application;
fig. 4 is a flow chart of ammonia slip amount correction based on a rear NOX sensor in a method for real-time estimation of ammonia slip amount at a rear end of a diesel SCR according to an embodiment of the present application.
Detailed Description
In order that those skilled in the art will better understand the present application, a technical solution in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
The embodiment of the application provides a real-time estimation method for the ammonia leakage quantity at the rear end of a diesel engine SCR, which can solve the problems that the real-time closed-loop correction control of SCR ammonia storage control cannot be ensured, the accurate control of urea injection quantity cannot be realized, and the expected emission result cannot be achieved in the related technology.
Fig. 1 is a real-time estimation method for ammonia slip amount at the rear end of SCR of a diesel engine according to an embodiment of the present application, which may include: calculating the ammonia leakage amount under the steady-state working condition; calculating the ammonia leakage amount under the transient working condition according to the ammonia leakage amount under the steady-state working condition; according to the ammonia under the transient working conditionLeakage and post NO X The sensor measurement corrects the ammonia slip. In the embodiment, through the calculation of the ammonia leakage amount based on the steady-state working condition, the calculation of the ammonia leakage amount based on the transient working condition and the correction of the ammonia leakage amount based on the rear NOx sensor, NH is improved after accurate calibration and optimization 3 Calculation accuracy of leakage amount, NH is realized 3 The real-time estimation of the leakage quantity ensures the closed-loop correction control of the SCR ammonia storage control, and realizes the accurate control of the urea injection quantity, thereby reaching the expected emission result.
Referring to FIG. 2, in some embodiments, the method for calculating the ammonia slip under steady state conditions may include: when the actual ammonia storage amount in the SCR catalyst exceeds the maximum ammonia storage amount of the SCR catalyst, calculating a first ammonia slip amount according to the actual ammonia storage amount in the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst; calculating a second ammonia slip from the ammonia coverage of the SCR catalyst when the ammonia coverage of the SCR catalyst exceeds a limit; and calculating the ammonia leakage amount under the steady-state working condition according to the first ammonia leakage amount and the second ammonia leakage amount.
In this embodiment, NH may occur when the actual ammonia storage amount within the SCR catalyst exceeds the SCR catalyst maximum ammonia storage amount 3 The leakage, namely calculating the ammonia leakage amount in real time under a steady-state working condition according to the actual ammonia storage amount in the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst; NH may also occur when ammonia coverage of the SCR catalyst exceeds a limit 3 The leakage, by calculating the second ammonia leakage amount according to the ammonia coverage rate of the SCR catalyst, the real-time calculation of the ammonia leakage amount under the steady-state working condition can be realized; the total ammonia leakage amount under the steady-state working condition can be obtained by adding the first ammonia leakage amount and the second ammonia leakage amount, and the NH is further improved by integrating the factors such as the actual ammonia storage amount inside the SCR catalyst, the maximum ammonia storage amount of the SCR catalyst, the ammonia coverage rate of the SCR catalyst and the like in the calculation process 3 Calculation accuracy of leakage amount, NH 3 The real-time calculation of the leakage is more accurate.
Referring to FIG. 2, in some embodiments, the first ammonia slip calculation method may beComprising the following steps: based on NH storage within SCR catalyst 3 Initial value of quantity and store NH 3 Calculating the actual ammonia storage amount inside the SCR catalyst at a rate; calculating the maximum ammonia storage amount of the SCR catalyst according to the correction coefficient of the ammonia storage amount, which is in base with the SCR catalyst, of the working volume of the SCR catalyst and the aging of the SCR catalyst; and calculating the first ammonia leakage amount according to the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst.
In this embodiment, the actual ammonia storage amount inside the SCR catalyst and the NH storage inside the SCR catalyst 3 Initial value of quantity and store NH 3 The maximum ammonia storage amount of the SCR catalyst is related to the basic maximum ammonia storage amount of the SCR catalyst, the working volume of the SCR catalyst and the ammonia storage amount correction coefficient of the aging of the SCR catalyst, after the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst are calculated, when the actual ammonia storage amount inside the SCR catalyst exceeds the maximum ammonia storage amount of the SCR catalyst, the ammonia leakage amount is equal to the total NH storage amount inside the SCR catalyst in the calculation process 3 Initial value of quantity, store NH 3 The NH is further improved by factors such as the speed, the maximum ammonia storage amount of the SCR catalyst base, the working volume of the SCR catalyst, the ammonia storage amount correction coefficient of the aging of the SCR catalyst and the like 3 Calculation accuracy of leakage amount, NH 3 The real-time calculation of the leakage is more accurate.
In other embodiments, the actual ammonia storage amount inside the SCR catalyst and the SCR catalyst maximum ammonia storage amount may also be derived in other ways, for example by measurement, experimentation or from a product specification.
Referring to fig. 2, in some embodiments, the method for calculating the second ammonia leakage amount may include: calculating the ammonia coverage rate of the SCR catalyst according to the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst; the second ammonia slip is calculated as a function of ammonia coverage of the SCR catalyst.
In this embodiment, only NH adsorbed on SCR catalyst 3 Can react with NOx in engine emission, and NH which is not adsorbed and desorbed 3 NH can occur 3 Escape fromEventually causing ammonia slip, the SCR catalyst typically indicates how much NH the SCR catalyst adsorbs by ammonia coverage 3 . When the ammonia coverage is high, the conversion efficiency of NOx is higher, but the higher the ammonia coverage increases the amount of ammonia slip. The ammonia coverage rate of the SCR catalyst is related to the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst, after the ammonia coverage rate of the SCR catalyst is calculated, the ammonia coverage rate of the SCR catalyst is calculated by utilizing the linear relation between the ammonia coverage rate of the SCR catalyst and the second ammonia leakage amount, namely the real-time ammonia leakage amount when the ammonia coverage rate of the SCR catalyst exceeds the limit under the steady-state working condition, and the NH is further improved by integrating the factors such as the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst in the calculation process 3 Calculation accuracy of leakage amount, NH 3 The real-time calculation of the leakage is more accurate.
Referring to FIG. 3, in some embodiments, the method for calculating the ammonia slip under the transient operating condition may include: and calculating the ammonia leakage amount under the transient working condition according to the ammonia leakage amount under the steady-state working condition, the ammonia leakage amount correction coefficient related to the catalyst temperature change rate and the sampling period.
In this embodiment, the ammonia slip under transient conditions is mainly related to the SCR catalyst temperature, and the more the SCR catalyst temperature changes, the more the ammonia slip. The ammonia leakage quantity under the steady-state working condition, the ammonia leakage quantity correction coefficient related to the catalyst temperature change rate and the sampling period are utilized to calculate the ammonia leakage quantity under the transient working condition, and the NH is further improved by integrating the factors such as the ammonia leakage quantity, the ammonia leakage quantity correction coefficient related to the catalyst temperature change rate, the sampling period and the like in the calculation process 3 Calculation accuracy of leakage amount, NH 3 The real-time calculation of the leakage is more accurate.
Referring to fig. 4, in some embodiments, the method for correcting the ammonia leakage amount may include: according to the post NO X Sensor measurement versus true NH 3 And identifying and calculating the leakage quantity.
In this embodiment, the post-introduction NOx sensor measurement value needs to be corrected to ensure final calculation in consideration of the ammonia slip amount calculation errorThe ammonia leakage amount obtained is accurate. Taking into account NH of the rear NOx sensor 3 Measuring cross sensitivity requires a true NH corresponding to the post NOx sensor measurement 3 After identification calculation and accurate calibration and optimization, NH is improved 3 Calculation accuracy of leakage amount, NH is realized 3 The real-time estimation of the leakage quantity ensures the closed-loop correction control of the SCR ammonia storage control, and realizes the accurate control of the urea injection quantity, thereby reaching the expected emission result.
Referring to FIG. 4, in some embodiments, the method is described in terms of the post NO X Sensor measurement versus true NH 3 The identifying calculation of the leakage amount may include: and when the measured value of the rear NOx sensor is smaller than a first threshold value, the measured value of the rear NOx sensor is the NOx concentration at the current moment. In this embodiment, when the post NOx sensor measurement is less than the threshold, then NOx and NH 3 Is in a very fully reacted stage within the SCR, where the post NOx measurement is considered to be the NOx concentration at the current time. By taking into account NH of the post-NOx sensor 3 Measuring cross sensitivity, for true NH corresponding to the measured value of the rear NOx sensor 3 Further identifying and calculating to further improve NH 3 The calculation accuracy of the leakage amount.
Referring to FIG. 4, in some embodiments, the method is described in terms of the post NO X Sensor measurement versus true NH 3 The identifying calculation of the leakage amount may include: and when the measured value of the rear NOx sensor is larger than a first threshold value, performing identification calculation according to the ammonia coverage rate level. In this embodiment, when the measured value of the post NOx sensor is greater than the first threshold, the recognition calculation is performed according to the ammonia coverage level, so as to determine whether the ammonia storage capacity in the SCR has reached the upper limit, thereby determining NH 3 Whether a large amount escapes, whether NOx is substantially completely reacted, and thus NH 3 Cross sensitivity to NOx sensor effects.
Referring to FIG. 4, in some embodiments, the performing the identification calculation based on the ammonia coverage level may include: when the ammonia coverage is less than a second threshold, then the post NOx sensor measurement is the current timeIn the present embodiment, when the post-NOx sensor measurement is above the first threshold and the ammonia coverage level is low, then the SCR is still capable of storing ammonia, NH 3 Less NH escapes 3 The cross sensitivity of the NOx sensor is less affected when the NOx sensor measurement is considered to be the NOx concentration at the current time. By taking into account NH of the post-NOx sensor 3 Measuring the cross sensitivity, further identifying and calculating the real NH3 corresponding to the measured value of the rear NOx sensor, and further improving the NH 3 The calculation accuracy of the leakage amount.
Referring to FIG. 4, in some embodiments, the performing the identification calculation based on the ammonia coverage level may include: when the ammonia coverage rate is greater than a second threshold value, calculating the real NH according to the ammonia leakage amount under the transient working condition, the post-NOx sensor measured value and a calculation weight correction coefficient 3 Leakage amount. In this embodiment, when the NOx sensor measurement is greater than the first threshold and the ammonia coverage is greater than the second threshold, the SCR internal ammonia storage capacity has reached the upper limit, NH 3 A large amount of slip, NOx, will be substantially fully reacted, at which point the NOx sensor measurement is considered to be substantially NH 3 Leakage amount, measured NH 3 Leakage value. Based on the post-NOx sensor measurements obtained from the test at this time, for an estimated NH 3 The leakage amount is corrected. Calculating the true NH according to the ammonia leakage amount, the measured value of the rear NOx sensor and the calculated weight correction coefficient under the transient working condition 3 Leakage amount. By taking account of the calculation error of the ammonia slip, the measured value of the NOx sensor after introduction is corrected, thereby further ensuring the accuracy of the ammonia slip obtained by final calculation, and taking account of the NH of the NOx sensor after introduction 3 Measuring the cross sensitivity, further identifying and calculating the real NH3 corresponding to the measured value of the rear NOx sensor, and further improving the NH 3 Calculation accuracy of leakage amount, NH is realized 3 And the leakage quantity is estimated in real time, so that the closed-loop correction control of the SCR ammonia storage control is ensured.
The method for accurately calculating the real-time estimation of the ammonia leakage quantity at the rear end of the SCR system comprises the following steps:
1. ammonia leakage calculation under steady-state working condition
The ammonia leakage under steady-state conditions is largely divided into two parts:
1) When the actual ammonia storage amount inside the SCR catalyst exceeds the SCR catalyst maximum ammonia storage amount, the ammonia slip amount is calculated at this time as:
m NH3_slip_base1 ＝m NH3_Store -m NH3_Capacity
m NH3_Capacity ＝m NH3_Capacity_base (T)×V SCR ×f SCR_aging
wherein:
m NH3Int for NH storage in calculated SCR catalyst 3 An initial value of the quantity;
for calculated NH storage 3 A rate;
m NH3_Capacity_base for maximum ammonia storage associated with SCR catalyst temperature, the maximum ammonia storage is mainly related to the characteristics of the carrier, the carrier temperature and the aging degree of the carrier;
V SCR a working volume for the SCR catalyst;
f SCR_aging and (5) correcting the coefficient for SCR catalyst aging.
2) Calculation of ammonia slip when the ammonia coverage of the SCR catalyst exceeds a limit
Only NH adsorbed on SCR catalyst 3 Can react with NOx in engine emission, and NH which is not adsorbed and desorbed 3 NH can occur 3 Escape, eventually causing ammonia leakage. SCR catalysts generally represent how much NH the SCR catalyst adsorbs by ammonia coverage 3 . When the ammonia coverage is high, the conversion efficiency of NOx is higher, but the higher the ammonia coverage increases the amount of ammonia slip.
m NH3_slip_base2 ＝f(θ NH3 )
By combining the above, the ammonia leakage amount in the steady state is calculated as:
m NH3_slip_Steady ＝m NH3_slip_base1 +m NH3_slip_base2
2. ammonia leakage amount calculation under transient working condition
The ammonia leakage change under the transient working condition is mainly related to the temperature of the SCR catalyst, and the more the temperature change of the SCR catalyst is, the more the ammonia leakage amount is, and the ammonia leakage amount under the transient working condition is:
m NH3_slip ＝{m NH3_slip_Steady (t)+m NH3_slip_Steady (t-1)×[1-f NH3_slip (t-1)]}×f NH3_slip (t)
where t is the sampling period, f NH3_slip The ammonia slip correction factor is correlated to the catalyst temperature change rate.
3, correction of ammonia leakage amount based on post NOx sensor
In view of the ammonia slip amount calculation error, the NOx sensor measurement value after introduction needs to be corrected to ensure the accuracy of the final calculated ammonia slip amount. Taking into account NH of the rear NOx sensor 3 Measuring cross sensitivity requires a true NH corresponding to the post NOx sensor measurement 3 And performing identification calculation.
a) When the post NOx sensor measurement is less than the threshold, then NOx and NH 3 The emission amount of the catalyst is low, the SCR is in a stage of just complete reaction, and the measured value of the rear NOx is considered to be the concentration of the NOx at the current moment;
b) When the post NOx sensor measurement is above a certain threshold and the ammonia coverage level is low, then the SCR is still capable of ammonia storage, NH 3 Less NH escapes 3 The cross sensitivity of the NOx sensor is less affected, and the measured value of the NOx sensor is considered to be the concentration of NOx at the current moment;
c) post-NOx sensor sensingThe magnitude is greater than the threshold value, and the ammonia coverage rate is greater than the threshold value, the ammonia storage capacity inside the SCR reaches the upper limit, NH 3 A large amount of slip, NOx, will be substantially fully reacted, at which point the NOx sensor measurement is considered to be substantially NH 3 Slip, measured NH3 slip value. Based on the post-NOx sensor measurements obtained from the test at this time, for an estimated NH 3 The leakage amount is corrected.
m NH3_slip_final ＝m NH3_slip +k×(NO X_measure -m NH3_slip )
The related sensor, the ammonia coverage rate threshold and the calculated weight correction coefficient K are obtained through qualitative adjustment and setting summary of multiple times of simulation tests and experiments.
In the description of the present application, it should be noted that the azimuth or positional relationship indicated by the terms "upper", "lower", etc. are based on the azimuth or positional relationship shown in the drawings, and are merely for convenience of describing the present application and simplifying the description, and are not indicative or implying that the apparatus or element in question must have a specific azimuth, be constructed and operated in a specific azimuth, and thus should not be construed as limiting the present application. Unless specifically stated or limited otherwise, the terms "mounted," "connected," and "coupled" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.
It should be noted that in the present application, relational terms such as "first" and "second" and the like are 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. Moreover, 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 one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The foregoing is only a specific embodiment of the application to enable those skilled in the art to understand or practice the 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 (10)
1. The real-time estimation method for the ammonia leakage amount at the rear end of the SCR of the diesel engine is characterized by comprising the following steps of:
calculating the ammonia leakage amount under the steady-state working condition;
calculating the ammonia leakage amount under the transient working condition according to the ammonia leakage amount under the steady-state working condition;
according to the ammonia leakage amount and the post NO under the transient working condition X The sensor measurement corrects the ammonia slip.
2. The method for estimating the ammonia slip amount at the rear end of the SCR of the diesel engine according to claim 1, wherein the method for calculating the ammonia slip amount under the steady-state condition comprises:
when the actual ammonia storage amount in the SCR catalyst exceeds the maximum ammonia storage amount of the SCR catalyst, calculating a first ammonia slip amount according to the actual ammonia storage amount in the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst;
calculating a second ammonia slip from the ammonia coverage of the SCR catalyst when the ammonia coverage of the SCR catalyst exceeds a limit;
and calculating the ammonia leakage amount under the steady-state working condition according to the first ammonia leakage amount and the second ammonia leakage amount.
3. The method for real-time estimation of ammonia slip at the SCR back end of a diesel engine according to claim 2, wherein the method for calculating the first ammonia slip comprises:
based on NH storage within SCR catalyst 3 Initial value of quantity and store NH 3 Calculating the actual ammonia storage amount inside the SCR catalyst at a rate;
calculating the maximum ammonia storage amount of the SCR catalyst according to the correction coefficient of the ammonia storage amount, which is in base with the SCR catalyst, of the working volume of the SCR catalyst and the aging of the SCR catalyst;
and calculating the first ammonia leakage amount according to the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst.
4. The method for real-time estimation of ammonia slip at the SCR back end of a diesel engine according to claim 2, wherein the calculation method of the second ammonia slip comprises:
calculating the ammonia coverage rate of the SCR catalyst according to the actual ammonia storage amount inside the SCR catalyst and the maximum ammonia storage amount of the SCR catalyst;
the second ammonia slip is calculated as a function of ammonia coverage of the SCR catalyst.
5. The method for estimating the ammonia slip amount at the rear end of the SCR of the diesel engine according to claim 1, wherein the method for calculating the ammonia slip amount under the transient condition comprises:
and calculating the ammonia leakage amount under the transient working condition according to the ammonia leakage amount under the steady-state working condition, the ammonia leakage amount correction coefficient related to the catalyst temperature change rate and the sampling period.
6. The method for estimating the ammonia slip amount at the rear end of the SCR of the diesel engine according to claim 1, wherein the correction method of the ammonia slip amount comprises:
according to the post NO X Sensor measurement versus true NH 3 And identifying and calculating the leakage quantity.
7. The method for real-time estimation of ammonia slip at the rear end of a diesel SCR according to claim 6, wherein said step is performed based on said post-NO X Sensor measurement versus true NH 3 The identification calculation of the leakage amount comprises the following steps:
and when the measured value of the rear NOx sensor is smaller than a first threshold value, the measured value of the rear NOx sensor is the NOx concentration at the current moment.
8. The method for real-time estimation of ammonia slip at the rear end of a diesel SCR according to claim 6, wherein said step is performed based on said post-NO X Sensor measurement versus true NH 3 The identification calculation of the leakage amount comprises the following steps:
and when the measured value of the rear NOx sensor is larger than a first threshold value, performing identification calculation according to the ammonia coverage rate level.
9. The method for real-time estimation of ammonia slip at the rear end of a diesel SCR according to claim 8, wherein the performing the identification calculation according to the ammonia coverage level comprises:
and when the ammonia coverage rate is smaller than a second threshold value, the measured value of the rear NOx sensor is the NOx concentration at the current moment.
10. The method for real-time estimation of ammonia slip at the rear end of a diesel SCR according to claim 8, wherein the performing the identification calculation according to the ammonia coverage level comprises:
when the ammonia coverage rate is greater than a second threshold value, the post NOx sensor measurement value is NH at the current time 3 A leakage value; calculating the real NH according to the ammonia leakage amount under the transient working condition, the measured value of the rear NOx sensor and the calculated weight correction coefficient 3 Leakage amount.
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