CN113607398A - Method for accurately measuring SCR ammonia injection ratio - Google Patents
Method for accurately measuring SCR ammonia injection ratio Download PDFInfo
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- CN113607398A CN113607398A CN202110887002.7A CN202110887002A CN113607398A CN 113607398 A CN113607398 A CN 113607398A CN 202110887002 A CN202110887002 A CN 202110887002A CN 113607398 A CN113607398 A CN 113607398A
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- G—PHYSICS
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M13/00—Testing of machine parts
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M15/00—Testing of engines
- G01M15/04—Testing internal-combustion engines
- G01M15/042—Testing internal-combustion engines by monitoring a single specific parameter not covered by groups G01M15/06 - G01M15/12
Abstract
The invention relates to a method for accurately measuring the SCR ammonia injection proportion, which stabilizes the working condition in a set range; calculating the theoretical injection quantity of ammonia under the current working condition on the assumption that the SCR target efficiency under the current working condition is 1; continuously increasing the injection amount of ammonia on the basis of the theoretical injection amount until ammonia leakage occurs, and obtaining the stable conversion efficiency of the SCR under the current working condition; starting to inject by using the theoretical injection quantity of ammonia, determining the following condition of Feff and Fref, and continuously performing closed-loop control by using the deviation of the Feff and the Fref on the premise of no ammonia leakage to obtain that the injection quantity coefficient is stabilized at a certain value; obtaining current working condition NH3Coefficient of proportionality with NOx. The technical scheme obtains accurate NH by changing the measurement method and thought3The reaction proportion coefficient with NOx is beneficial to accurately controlling urea injection and efficiency stability, and the closed-loop negative correction is added to reduce the positive compensation probability while ensuring that the SCR efficiency is exerted to the maximum extent, so that the ammonia leakage risk is reduced.
Description
Technical Field
The invention belongs to the technical field of diesel engine SCR systems, and particularly relates to a method for accurately measuring SCR ammonia injection proportion.
Background
The treatment of nitrogen oxides (NOx) in exhaust gases by diesel engines using SCR (selective catalytic reduction) systems by hydrolysis of urea to NH becomes a popular means of emission control today3The main reducing substances react with NOx at proper temperature and flow rate to generate N2And H2Discharging substances such as O and the like. The copper-based SCR system is composed of main functional units such as CuO and related sensors.
NH3Injection ratio i.e. at different temperatures, flow rates, NO2For NH under different working conditions such as NOx proportion and the like3Injection to NOx reaction ratio upstream of the SCR (which may also be referred to as ammonia-to-nitrogen ratio).
When the temperature of the vehicle reaches a certain temperature in the using process, ammonia injection and hydrolysis are started to generate NH3Reacts with NOx. Currently, the SCR system is used for closed-loop control of NH3And (4) jetting precision. Namely, the modeling comprises the following steps: SCR efficiency, NH3The current required ammonia injection amount is calculated according to the reaction proportion of NOx, the selection of an ammonia storage target value, an upstream NOx value (an SCR upstream NOx model is established through universal characteristics when a NOx sensor is not released) and the exhaust gas flow. And after a certain exhaust temperature is reached, closed-loop compensation is carried out by monitoring the deviation between a tail pipe NOx model (calculated by an upstream NOx and SCR efficiency model) and a tail pipe NOx sensor value. Finally realize NH3And controlling the injection.
Prior art due to NH3The deviation of the calibration of the injection reaction ratio (mainly the deviation of the calculation method from the actual reaction ratio) leads to an accumulation of NH3Storage bias, because the applicability of the closed loop system is different between different regions, e.g. low temperature region is not closed due to aging and other influencing factors (e.g. THC, S)And (4) controlling a loop. The resulting deviation is highly susceptible to ammonia slip. Meanwhile, due to the fact that the national six regulation limit value is small, the efficiency of the SCR in most high-efficiency areas reaches 100%, if active spray reduction is not carried out, the SCR enters a closed-loop interval, then a closed-loop control method in the high-efficiency areas, namely, an efficiency model is used as a target value to carry out closed-loop, and the phenomenon that the closed-loop is compensating excessive deteriorated ammonia leakage is easily caused.
Disclosure of Invention
The invention aims to provide a method for accurately measuring the ammonia injection ratio of SCR (selective catalytic reduction) so as to solve the problem of NH (NH) in the prior art3Injection reaction ratio calibration deviation and closed-loop control method lead to accumulated NH3Storage deviations ultimately create problems with ammonia leaks or regulatory risks.
In order to realize the purpose, the invention is realized by the following technical scheme:
a method of accurately determining an SCR ammonia injection ratio, comprising the steps of:
s1, increasing the exhaust temperature and stopping injecting urea to empty the SCR;
s2, stabilizing the working condition at the exhaust temperature which is the first set temperature, and stabilizing the exhaust gas flow at the first set flow;
s3, assuming that the SCR target efficiency Fref reaches 100% under the current working condition, and adopting the method that the NO ratio in the current NOx is 100% and NH3The initial value of the calculated molar mass ratio theta fac for reaction is M, and the NH under the current working condition is calculated3The theoretical injection quantity Urea _ dm of (1);
s4 as NH3Based on the theoretical injection quantity Urea _ dm, NH is continuously used3Is increased by NH by a multiple K of the theoretical injection quantity Urea _ dm3Until ammonia leakage occurs, obtaining the stable conversion efficiency FMax of the SCR with the maximum working condition at present, and changing the target SCR efficiency FMef to a value smaller than or equal to FMax;
s5 as NH3The theoretical injection quantity Urea _ dm, determines that Feff follows Fref without NH3Continuously performing closed-loop control by using the deviation of the two on the premise of leakage; if the Feff is smaller than the Fref, gradually increasing the injection quantity coefficient alpha; if Feff is larger than or equal to Fref, the injection quantity coefficient alpha is gradually reduced, and finallyFinally, alpha is stabilized at a set value, based on the actual reaction process, the chemical reaction in the SCR is a non-single reaction, and the alpha value is between 0.6 and 1;
s6, obtaining the current working condition NH3The reaction rate coefficient θ fac with NOx is M × α.
Further, before proceeding to step S1, NH is added to the tail pipe3A sensor.
Further, in step S2, the first set temperature is 300 ℃ and the first set flow rate is 200 kg/hr.
Further, in step S3, M is 0.57.
Further, in step S3, the current operating condition NH3The calculation formula of the theoretical injection quantity Urea _ dm is as follows:
mEg x λ Us x β x Fmef x θ fac x 5.425, wherein mEg is exhaust mass flow, λ Us is measurement of an SCR upstream nox sensor, β is a dimensionless coefficient of 0.00044 for converting ppm units in mg/s units, Fmef is controllable target SCR efficiency, θ fac is NH3Coefficient of proportionality with NOx, 5.425 NH under current operating conditions3Mass conversion ratio to urea.
Further, the multiple K is one of the arithmetic progression of 1.1, 1.2, 1.3 … ….
Further, step S41 is included before step S5, and urea injection is stopped again until the NOx values before and after SCR are consistent.
The invention has the beneficial effects that:
the technical scheme obtains accurate NH by changing the measurement method and thought3The reaction proportion coefficient with NOx is beneficial to accurately controlling urea injection and efficiency stability, and the closed-loop negative correction is added to reduce the positive compensation probability while ensuring that the SCR efficiency is exerted to the maximum extent, so that the ammonia leakage risk is reduced.
The technical scheme is an openness testing method, and has universal applicability to different post-processing technical routes. Meanwhile, an extremely accurate statistical research basis is provided for SCR target efficiency control and reaction proportion coefficient corresponding relation.
Drawings
FIG. 1 is a schematic view of an SCR structure according to the present invention;
FIG. 2 is a flow chart of a method of accurately determining SCR ammonia injection ratio according to the present invention;
FIG. 3 is a logic flow diagram of a method of accurately determining the SCR ammonia injection ratio in accordance with the present invention.
Description of the reference numerals
1. Front NOx sensor, 2, urea injector, 3, rear NOx sensor.
Detailed Description
The technical solutions of the present invention are described in detail below by examples, and the following examples are only exemplary and can be used only for explaining and explaining the technical solutions of the present invention, but not construed as limiting the technical solutions of the present invention.
In the following precise assay of the present application, instruments, devices, reagents and the like used, unless otherwise specified, are commercially available.
According to the technical scheme, through calibration and measurement means, after certain exhaust temperature and unfreezing conditions are achieved and the pressure of the pump injection system is established and checked, ammonia injection is started and NOx conversion is carried out. By establishing a precise model including SCR efficiency, NH3The current ammonia injection amount is calculated in proportion to the NOx reaction, upstream NOx value (SCR upstream NOx model is established by all characteristics when NOx sensor is not released). And after a certain exhaust temperature is reached, closed-loop compensation is carried out by monitoring the deviation between a tail pipe NOx model (adding negative correction) and a tail pipe NOx sensor value. Finally realize NH3And (4) precise control.
The SCR working principle is as follows:
when the exhaust temperature reaches a threshold, there is no demand for defrost and the pump system completes the pressure build-up and checks for an error, urea injection is turned on and reacts with NOx in the carrier as follows:
and (3) hydrolysis reaction:
the catalytic reduction reaction includes the following reaction forms:
NO2+NO+2NH3→2N2+3H2O；
6NO2+8NH3→7N2+12H2O；
NO+2NH3+NO2→2N2+3H2O；
4NO+4NH3+O2→4N2+6H2O。
the technical solution of the present application is open, and in the following examples, the operating condition of 300 ℃ and exhaust gas flow rate of 200 kg/hour is taken as an example, and this operating condition is merely an example of the technical solution, and is not applicable to the technical solution of the present application under other operating conditions.
The application provides a method for accurately determining the SCR ammonia injection ratio, as shown in FIG. 2 and FIG. 3, comprising the following steps:
s1, before accurate measurement, adding NH on the tail pipe of the engine3The sensor, meanwhile, a front NOx sensor 1, a urea nozzle 2 and a rear NOx sensor 3 are arranged on the SCR of the tail pipe of the engine, as shown in fig. 1, and these parts are all conventional configurations of the existing SCR, and will not be described in detail.
First, improve tail gas exhaust temperature and stop to spray urea to empty SCR, the improvement tail gas exhaust temperature here does not carry out the settlement of temperature, adopts the 300 ℃ temperature that is higher than the schematic operating mode of this embodiment usually, and the data that specifically exceeds do not emphasize, as long as the realization can empty SCR to guarantee not to cause the thermal damage homoenergetic to this technical scheme that can realize this application to the accessory part that engine exhaust discharged. After the SCR is emptied, the consistency of NOx before and after the SCR is ensured.
And S2, stabilizing the working condition at the exhaust temperature of 300 ℃ and the exhaust gas flow rate of 200 kg/h.
S3, assuming that the SCR target efficiency Fref reaches 100% under the current working condition (the part is the theoretical calculation stage, and the actual SCR target efficiency Fref cannot reach 100%), adopting the initial value of theta fac of the standard reaction molar mass ratio as M, wherein in the embodiment, the value of M is 0.57, and calculating NH under the current working condition3The theoretical injection amount Urea _ dm of (1).
Current operating mode NH3The calculation formula of the theoretical injection quantity Urea _ dm is as follows:
mEg x λ Us x β x Fmef x θ fac x 5.425, wherein mEg is exhaust mass flow, λ Us is measurement of an SCR upstream nox sensor, β is a dimensionless coefficient of 0.00044 for converting ppm units in mg/s units, Fmef is controllable target SCR efficiency, θ fac is NH3Coefficient of proportionality with NOx, 5.425 NH under current operating conditions3Mass conversion ratio to urea.
S4 using NH as described above3Based on the theoretical injection quantity Urea _ dm, NH is continuously used3Is increased by NH by a multiple K of the theoretical injection quantity Urea _ dm3In the present application, the value of the multiple K is an arithmetic progression of 1.1, 1.2, 1.3, 1.4 … …, specifically: firstly according to NH31.1 times the theoretical injection quantity Urea _ dm, and secondly as NH31.2 times of the theoretical injection quantity Urea _ dm, third as NH3Injecting 1.3 times of the theoretical injection quantity Urea _ dm in the mode until ammonia leakage occurs, obtaining the stable conversion efficiency FMax of the SCR with the maximum current working condition, and changing the target SCR efficiency FMef to be a value smaller than or equal to FMax. In other embodiments of the present application, the value of the multiple K may also be increased according to other arithmetic progression, so as to ensure the stability of the detection result, only in NH3The theoretical injection amount Urea _ dm may be increased by an equal amount.
And S41, stopping urea injection again until the NOx values before and after SCR are consistent, wherein the exhaust temperature can be carried out according to the current working condition or according to the mode of increasing the exhaust temperature in the step S1.
S5 as NH3The theoretical injection quantity Urea _ dm, determines that Feff follows Fref without NH3Continuously performing closed-loop control by using the deviation of the two on the premise of leakage; if the Feff is smaller than the Fref, gradually increasing the injection quantity coefficient alpha; if Feff is greater than or equal to Fmef, the injection quantity coefficient alpha is gradually reduced, and finally alpha is stabilized at a certain value. Based on the actual reaction, the chemical process in SCR is not a single reaction, so the value of alpha is generally between 0.6 and 1. Testing with my partyTaking the test result of the post-treatment carried by a certain type of engine as an example, the exhaust temperature is 350 ℃, and the alpha value is 0.7 in the working condition test of the exhaust gas mass flow of 180 kg/hour; the exhaust temperature is 420 ℃, and the alpha value of the test of the working condition of 325 kg/hour of the mass flow of the waste gas is 0.72.
S6, obtaining the current working condition NH3The reaction rate coefficient θ fac with NOx is M × α, i.e., θ fac is 0.57 × α.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (7)
1. A method for accurately determining an SCR ammonia injection ratio, comprising the steps of:
s1, increasing the exhaust temperature and stopping injecting urea to empty the SCR;
s2, stabilizing the working condition at the exhaust temperature which is the first set temperature, and stabilizing the exhaust gas flow at the first set flow;
s3, assuming that the SCR target efficiency Fref reaches 100% under the current working condition, and adopting the method that the NO ratio in the current NOx is 100% and NH3The initial value of the calculated molar mass ratio theta fac for reaction is M, and the NH under the current working condition is calculated3The theoretical injection quantity Urea _ dm of (1);
s4 as NH3Based on the theoretical injection quantity Urea _ dm, NH is continuously used3Is increased by NH by a multiple K of the theoretical injection quantity Urea _ dm3Until ammonia leakage occurs, obtaining the stable conversion efficiency FMax of the SCR with the maximum working condition at present, and changing the target SCR efficiency FMef to a value smaller than or equal to FMax;
s5 as NH3The theoretical injection quantity Urea _ dm, determines that Feff follows Fref without NH3Continuously performing closed-loop control by using the deviation of the two on the premise of leakagePreparing; if the Feff is smaller than the Fref, gradually increasing the injection quantity coefficient alpha; if the Feff is larger than or equal to the Fref, gradually reducing the injection quantity coefficient alpha, and finally realizing that the alpha is stabilized at a set value, wherein the chemical reaction in the SCR is a non-single reaction based on the actual reaction process, and the alpha value is between 0.6 and 1;
s6, obtaining the current working condition NH3The reaction rate coefficient θ fac with NOx is M × α.
2. The method for accurately determining the SCR ammonia injection ratio of claim 1, wherein NH is added to the tail pipe before step S1 is performed3A sensor.
3. The method for accurately determining the SCR ammonia injection ratio according to claim 1, wherein the first set temperature is 300 ℃ and the first set flow rate is 200 kg/hr in step S2.
4. The method for accurately determining the SCR ammonia injection ratio of claim 1, wherein M is 0.57 in step S3.
5. The method for accurately determining the SCR ammonia injection ratio of claim 1, wherein in step S3, the current operating condition NH3The calculation formula of the theoretical injection quantity Urea _ dm is as follows:
the Urea _ dm is mEg × λ Us × β × Fmef × θ fac × 5.425, where mEg is exhaust mass flow, λ Us is a measurement value of an SCR upstream NOx sensor, β is a dimensionless coefficient, 0.00044 for converting ppm units to mg/s units, Fmef is a controllable target SCR efficiency, θ fac is a coefficient of a reaction ratio of NH3 to NOx, and 5.425 is a mass conversion ratio of NH3 to Urea under the current operating condition.
6. The method for accurately determining the SCR ammonia injection ratio of claim 1, wherein the multiple K in step S4 is one of an arithmetic series of 1.1, 1.2, 1.3 … ….
7. The method for accurately determining the SCR ammonia injection rate of claim 1, wherein step S5 is preceded by step S41 of stopping urea injection again until the NOx values before and after SCR match.
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Citations (4)
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|---|---|---|---|---|
| WO2008043928A1 (en) * | 2006-10-13 | 2008-04-17 | Peugeot Citroën Automobiles SA | Method for the closed-loop control of a urea amount for a nitrogen oxide processing system |
| CN112145269A (en) * | 2020-07-20 | 2020-12-29 | 无锡伟博汽车科技有限公司 | NO in diesel engine exhaust2Method for calculating urea injection quantity through proportion calculation |
| CN112240235A (en) * | 2019-07-17 | 2021-01-19 | 上海汽车集团股份有限公司 | SCR control method and device |
| CN112380498A (en) * | 2020-11-04 | 2021-02-19 | 无锡伟博汽车科技有限公司 | Algorithm for judging reasonability of urea injection amount of commercial diesel vehicle |
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- 2021-08-03 CN CN202110887002.7A patent/CN113607398B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008043928A1 (en) * | 2006-10-13 | 2008-04-17 | Peugeot Citroën Automobiles SA | Method for the closed-loop control of a urea amount for a nitrogen oxide processing system |
| CN112240235A (en) * | 2019-07-17 | 2021-01-19 | 上海汽车集团股份有限公司 | SCR control method and device |
| CN112145269A (en) * | 2020-07-20 | 2020-12-29 | 无锡伟博汽车科技有限公司 | NO in diesel engine exhaust2Method for calculating urea injection quantity through proportion calculation |
| CN112380498A (en) * | 2020-11-04 | 2021-02-19 | 无锡伟博汽车科技有限公司 | Algorithm for judging reasonability of urea injection amount of commercial diesel vehicle |
Non-Patent Citations (1)
| Title |
|---|
| 倪计民 等: "柴油机氨基SCR化学反应特性的试验研究", 《车用发动机》 * |
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