CN112459871A - Method for calculating reaction rate and method for controlling urea feeding amount of engine - Google Patents
Method for calculating reaction rate and method for controlling urea feeding amount of engine Download PDFInfo
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- CN112459871A CN112459871A CN202011293219.7A CN202011293219A CN112459871A CN 112459871 A CN112459871 A CN 112459871A CN 202011293219 A CN202011293219 A CN 202011293219A CN 112459871 A CN112459871 A CN 112459871A
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- 238000006243 chemical reaction Methods 0.000 title claims abstract description 226
- 238000000034 method Methods 0.000 title claims abstract description 29
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 title claims abstract description 15
- 239000004202 carbamide Substances 0.000 title claims abstract description 15
- 239000003054 catalyst Substances 0.000 claims abstract description 26
- 238000004364 calculation method Methods 0.000 claims abstract description 17
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 355
- 229910021529 ammonia Inorganic materials 0.000 claims description 141
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 claims description 131
- 229910000069 nitrogen hydride Inorganic materials 0.000 claims description 80
- 238000003795 desorption Methods 0.000 claims description 46
- 238000001179 sorption measurement Methods 0.000 claims description 45
- GQPLMRYTRLFLPF-UHFFFAOYSA-N Nitrous Oxide Chemical compound [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 claims description 40
- 239000007789 gas Substances 0.000 claims description 24
- 238000007254 oxidation reaction Methods 0.000 claims description 16
- 230000004913 activation Effects 0.000 claims description 11
- AVXURJPOCDRRFD-UHFFFAOYSA-N Hydroxylamine Chemical class ON AVXURJPOCDRRFD-UHFFFAOYSA-N 0.000 claims description 3
- 230000003647 oxidation Effects 0.000 claims description 3
- 239000001272 nitrous oxide Substances 0.000 claims description 2
- 238000010531 catalytic reduction reaction Methods 0.000 description 13
- 230000008569 process Effects 0.000 description 4
- 238000006555 catalytic reaction Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 238000004088 simulation Methods 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 238000002336 sorption--desorption measurement Methods 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 210000002700 urine Anatomy 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
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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]
- F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
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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
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/14—Nitrogen oxides
-
- 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
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Exhaust Gas After Treatment (AREA)
Abstract
The application relates to the field of engines, and discloses a method for calculating chemical reaction rate of an SCR system and a method for controlling urea introduction amount of an engine. The method for calculating the chemical reaction rate of the SCR system comprises the following steps: determining a parameter set according to the catalyst; determining a first reaction rate based on the first set of parameters and a second reaction rate based on the second set of parameters; determining a chemical reaction rate of the SCR system based on the first reaction rate and the second reaction rate. The calculation method can solve the problem that the reaction rate calculated by the existing chemical reaction kinetic physical model cannot truly reflect the actual chemical reaction condition of the engine.
Description
Technical Field
The application relates to the field of engines, in particular to a method for calculating chemical reaction rate of an SCR system and a method for controlling urea introduction amount of an engine.
Background
SCR (Selective Catalytic Reduction) utilizes NH3And NOx (nitrogen oxides) to reduce or even eliminate NOx in the exhaust of engines, such as diesel engines, to meet emissions requirements of state IV and above. Generally, the SCR system is mainly divided into four parts, namely a control unit, a urea dosage unit, a mixing device of urea and exhaust gas and a catalytic reaction unit according to functions. Wherein the urine is supplied according to the control of the control unitThe urea sprayed by the element dosage unit is mixed with the exhaust gas of the diesel engine in the mixing device, so that the urea aqueous solution and the exhaust gas are subjected to hydrolysis reaction to generate reducing agent ammonia gas for catalytic reduction reaction, and in the catalytic reaction unit, the ammonia gas reduces nitrogen oxide into nitrogen gas under the action of a catalyst, so that the tail gas of the diesel engine meets the emission regulation.
In an SCR system, an ammonia adsorption-desorption chemical reaction kinetic physical model in a catalytic reaction unit is the core of current engine emission control, and the existing chemical reaction kinetic physical model establishes a chemical reaction mechanism on a catalyst by using a single active site and a group of control parameters. The chemical reaction dynamics physical model enables the ammonia adsorption/desorption rate constant and the ammonia coverage rate obtained by a single active site to be not accurate enough, and then the chemical reaction rate of the SCR system obtained by calculation under the model cannot truly reflect the internal reaction condition of the engine, so that the working condition adaptability and the control robustness of the chemical reaction physical model are influenced to be not good enough, the NOx emission control is influenced, and the OBD false alarm is likely to be relatively high.
Disclosure of Invention
The application discloses a method for calculating the chemical reaction rate of an SCR system and a method for controlling the urea feeding amount of an engine, which are used for solving the problem that the actual chemical reaction condition of the engine cannot be truly reflected by the reaction rate calculated by utilizing the conventional chemical reaction kinetic physical model.
In order to achieve the purpose, the application provides the following technical scheme:
a method for calculating chemical reaction rate of an SCR system comprises the following steps:
determining a parameter set according to the catalyst; wherein the catalyst comprises a first active site and a second active site, the parameter set comprises a first set of parameters corresponding to a chemical reaction at the first active site and a second set of parameters corresponding to a chemical reaction at the second active site;
determining a first reaction rate based on the first set of parameters and a second reaction rate based on the second set of parameters;
determining a chemical reaction rate of the SCR system based on the first reaction rate and the second reaction rate.
Further, the determining a chemical reaction rate of the SCR system from the first reaction rate and the second reaction rate includes:
determining the chemical reaction rate from the sum of the first reaction rate and the second reaction rate.
Further, the chemical reaction rates include an ammonia adsorption reaction rate, an ammonia desorption reaction rate, a nitrogen oxide reaction rate, and an ammonia oxidation reaction rate, the first reaction rate includes a first ammonia adsorption rate, a first ammonia desorption rate, a first nitrogen oxide reaction rate, and a first ammonia oxidation reaction rate, and the second reaction rate includes a second ammonia adsorption rate, a second ammonia desorption rate, a second nitrogen oxide reaction rate, and a second ammonia oxidation reaction rate; wherein,
determining the ammonia adsorption reaction rate according to the sum of the first ammonia adsorption rate and the second ammonia adsorption rate;
determining the ammonia desorption reaction rate according to the sum of the first ammonia desorption rate and the second ammonia desorption rate;
determining the nitrogen oxide reaction rate from the sum of the first nitrogen oxide reaction rate and the second nitrogen oxide reaction rate;
determining the ammoxidation reaction rate according to the sum of the first ammoxidation reaction rate and the second ammoxidation reaction rate.
Further, the first ammonia adsorption rate r1 aComprises the following steps: r is1 a＝ka 1C NH3(1-θ1 NH3)，
Wherein, CNH3Is NH in the gas phase3Volume concentration; theta1 NH3Is NH at the first active site3Surface coverage; k is a radical ofa 1Is an adsorption rate factor on the first active site;
the second ammonia adsorption rate r2 aComprises the following steps: r is2 a＝ka 2C NH3(1-θ2 NH3)，
Wherein, CNH3Is NH in the gas phase3Volume concentration; theta2 NH3Is NH in the second active site3Surface coverage; k is a radical ofa 2Is an adsorption rate factor on the second active site;
the ammonia adsorption reaction rate raComprises the following steps: r isa＝r1 a+r2 a。
Further, the first ammonia desorption rate r1 dComprises the following steps: r is1 d＝kd 1exp[(-Ed 1/RT)(1-α1θ1 NH3]θ1 NH3，
Wherein k isd 1Is a first active site ammonia desorption rate factor, Ed 1Is the first active site ammonia desorption reaction activation energy, alpha1Is the heterogeneity constant, θ, corresponding to the first active site1 NH3Is NH at the first active site3Surface coverage, R is the ideal gas constant, T is the temperature;
the second ammonia desorption rate r2 dComprises the following steps: r is2 d＝kd 2exp[(-Ed 2/RT)(1-α1θ2 NH3]θ2 NH3，
Wherein k isd 2Is a second active site ammonia desorption rate factor, Ed 2Is the second active site ammonia desorption reaction activation energy, alpha2Is a heterogeneity constant, θ, corresponding to the second active site2 NH3Is NH in the second active site3Surface coverage, R is the ideal gas constant, T is the temperature;
the ammonia desorption reaction rate rdComprises the following steps: r isd＝r1 d+r2 d。
Further, the first nitrogen oxide reaction rate R1 NoxComprises the following steps: r1 NOx＝r1 NOxC1 sθ1 NH3，
Wherein r is1 NOxIs the first nitrogen oxide reaction rate constant, r1 NOx＝C1sRTKNOxexp(-ENOx/RT)，C1 sAmmonia storage capacity for the first active site of an SCR system, ENOxIs the activation energy of the first nitrogen oxide reaction, KNOxIs the reaction rate factor, θ, of the first nitrogen oxide reaction1 NH3Ammonia coverage of the first active site, R being the ideal gas constant, T being the temperature;
the second oxynitride reaction rate R2 NoxComprises the following steps: r2 NOx＝r2 NOxC2 sθ2 NH3，
Wherein r is2 NOxIs the first nitrogen oxide reaction rate constant, r2 NOx＝C2sRTKNOxexp(-ENOx/RT)，C2 sAmmonia storage capacity for the second active site of the SCR system, ENOxActivation energy for the second nitroxide reaction, KNOxIs the reaction rate factor, theta, of the second nitrous oxide reaction2 NH3Ammonia coverage of the second active site.
Further, the nitrogen oxide reaction rate RNOx,Comprises the following steps:
RNOx＝R1 NOx+R2 NOx＝RTKNOxexp(-ENOx/RT)(C1 sθ1 NH3+C2 sθ2 NH3)。
further, the first ammonia oxidation rate R1 OxComprises the following steps: r1 Ox＝r1 Oxθ1 NH3，
Wherein r is1 OxIs the first ammoxidation rate constant, r1 Ox＝C1 cKOxexp(-EOx/RT)，C1 cAmmonia storage capability for a first active site of an SCR system，EOxActivation energy of the first ammoxidation reaction, KOxIs a first ammoxidation rate factor, theta1 NH3Ammonia coverage of the first active site, R being the ideal gas constant, T being the temperature;
the second ammoxidation rate R2 OxComprises the following steps: r2 Ox＝r2 Oxθ2 NH3，
Wherein r is2 OxIs the second ammoxidation reaction rate constant, r2 Ox＝C2cKOxexp(-EOx/RT)，C2 cFor ammonia storage capacity of a second active site in the SCR system, EOxActivation energy for the second ammoxidation reaction, KOxIs a second ammoxidation reaction rate factor, θ2 NH3Ammonia coverage of the second active site.
Further, the ammoxidation reaction rate ROxComprises the following steps:
ROx＝R1 Ox+R2 Ox＝KOxexp(-EOx/RT)(C1 cθ1 NH3+C2 cθ2 NH3)。
a method for controlling urea flow of an engine, comprising:
the chemical reaction rate of the SCR system is calculated using the calculation method described in the present application,
and controlling the introduction amount of the urea according to the obtained chemical reaction rate.
By adopting the technical scheme of the application, the beneficial effects are as follows:
according to the calculation method, the adsorption/desorption physical model of ammonia in the SCR system is divided into the double active sites, the chemical reaction rate of the SCR system is calculated by utilizing two groups of parameters under the double active sites, and the calculated value can be closer to the actual working condition of an engine, so that the working condition adaptability and the control robustness of the physical model are improved, the NOx emission control is improved, and the possibility of OBD false alarm is reduced.
Drawings
FIG. 1 is a schematic illustration of a catalytic reduction chemical reaction provided by one embodiment of the present application;
FIG. 2 is a graph showing the variation of ammonia storage amount after isothermal adsorption for 30min at different temperatures in the same SCR system;
FIG. 3 is a graph showing the variation of ammonia storage amount after isothermal adsorption for 30min at different temperatures in the same SCR system;
FIG. 4 is a graph showing the variation of ammonia coverage with time of two active sites during the adsorption and desorption of ammonia gas at 100 ℃ in an SCR system;
FIG. 5 is a graph of results of comparing different reaction models with actual engine test values.
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.
It should be noted that: in the present application, all embodiments and preferred methods mentioned herein can be combined with each other to form new solutions, if not specifically stated. In the present application, all the technical features mentioned herein as well as preferred features may be combined with each other to form new technical solutions, if not specifically stated. In the present application, percentages (%) or parts refer to percent by weight or parts by weight relative to the composition, unless otherwise specified. In the present application, the components referred to or the preferred components thereof may be combined with each other to form new embodiments, if not specifically stated. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "6 to 22" means that all real numbers between "6 to 22" have been listed herein, and "6 to 22" is simply a shorthand representation of the combination of these values. The "ranges" disclosed herein may be in the form of lower limits and upper limits, and may be one or more lower limits and one or more upper limits, respectively. In the present application, the individual reactions or process steps may be performed sequentially or in sequence, unless otherwise indicated. Preferably, the reaction processes herein are carried out sequentially.
Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present application.
For the selective catalytic reduction reaction in the SCR system, whether vanadium-based or copper-based is used as the catalyst, there are two active sites, namely weak active site (Lewis active site) and strong active site (Bronsted active site), and the chemical reaction parameters of the two active sites, including the adsorption rate constant of ammonia, desorption activation energy of ammonia, coverage rate of ammonia, desorption pre-factor and heterogeneity constant, are different. In the chemical reaction kinetic physical model established on the basis of single active site at present, most of the chemical reaction kinetic physical model is calculated on the basis of strong active site, and chemical reaction on weak active site is completely ignored. The inventor of the application discovers through practice that when a chemical reaction dynamic physical model established by a single active site is used for controlling various items, abnormal NOx emission control often occurs, and the OBD system has high false alarm rate, and the problems are generally caused by the fact that the calculated value of the current chemical reaction dynamic physical model is not matched with the working condition of an actual engine.
Accordingly, the present application provides a method for calculating a chemical reaction rate of an SCR system, the method comprising the steps of:
step S1) determining a parameter set from the catalyst; wherein the catalyst comprises a first active site and a second active site, the parameter set comprises a first set of parameters corresponding to a chemical reaction at the first active site and a second set of parameters corresponding to a chemical reaction at the second active site;
step S2) determining a first reaction rate based on the first set of parameters and a second reaction rate based on the second set of parameters;
step S3) determines a chemical reaction rate of the SCR system based on the first reaction rate and the second reaction rate.
Wherein the first set of parameters corresponds to parameters at a first active site (weak active site) of the catalyst, and the second set of parameters corresponds to parameters at a second active site (strong active site) of the catalyst.
Wherein, in one embodiment of the present application, the determining the chemical reaction rate of the SCR system from the first reaction rate and the second reaction rate comprises: determining the chemical reaction rate from the sum of the first reaction rate and the second reaction rate.
The calculation method can synthesize the chemical reaction under the first active site and the chemical reaction under the second active site, so that the chemical reaction rate of the SCR system under the model can be more closely reflected to the chemical reaction under the actual working condition of the engine.
In one embodiment of the present application, the chemical reaction rates include an ammonia adsorption reaction rate, an ammonia desorption reaction rate, a nitrogen oxide reaction rate, and an ammonia oxidation reaction rate, the first reaction rate includes a first ammonia adsorption rate, a first ammonia desorption rate, a first nitrogen oxide reaction rate, and a first ammonia oxidation reaction rate, and the second reaction rate includes a second ammonia adsorption rate, a second ammonia desorption rate, a second nitrogen oxide reaction rate, and a second ammonia oxidation reaction rate; wherein the ammonia adsorption reaction rate is determined from the sum of the first ammonia adsorption rate and the second ammonia adsorption rate; determining the ammonia desorption reaction rate according to the sum of the first ammonia desorption rate and the second ammonia desorption rate; determining the nitrogen oxide reaction rate from the sum of the first nitrogen oxide reaction rate and the second nitrogen oxide reaction rate; determining the ammoxidation reaction rate according to the sum of the first ammoxidation reaction rate and the second ammoxidation reaction rate.
The SCR system has three selective catalytic reduction chemistries as shown in fig. 1. During the SCR reaction, NH3Firstly, the catalyst is adsorbed on the surface of the catalyst, and NH is carried out at high and low temperature3The adsorption sites on the surface of the copper-based catalyst are different. NH at low temperature3Adsorbing toThe Lewis active site and the Bronsted active site are basically adsorbed on the Bronsted active site at high temperature, so that the sites actually participating in the catalytic reduction reaction at high and low temperatures for adsorbing ammonia are different, namely, the catalytic reduction reaction occurs at different positions of the catalyst at high and low temperatures.
Since nitrogen oxides NOx can only react with ammonia in the adsorbed state on the catalyst surface, ammonia is first adsorbed on the catalyst surface and can only react with gaseous or adsorbed NOx. Meanwhile, in the ammoxidation reaction, only the ammonia in the adsorption state adsorbed on the surface of the catalyst can perform the oxidation reaction with oxygen, so that in the catalytic reduction reaction of the SCR system, the coverage rate of the ammonia on the active sites of the catalyst plays a crucial role in the whole catalytic reduction reaction.
Fig. 2 is a curve showing the variation of ammonia storage amount after isothermal adsorption for 30min at different temperatures of the same SCR system, and fig. 3 is a curve showing the variation of ammonia storage amount after isothermal adsorption for 30min at different temperatures of the same SCR system. As can be seen from fig. 2 and 3, the variation of the ammonia storage amount of different active sites at different temperatures gradually decreases the difference of the ammonia adsorption amount of the weak active site and the strong active site as the temperature increases, and therefore, the chemical reaction at any one of the active sites will have a greater influence on the catalytic reduction reaction of the whole SCR system.
Fig. 4 is a curve showing the change of ammonia coverage of two active sites with time during the adsorption and desorption process of ammonia gas at 100 ℃ in the SCR system, and it can be seen from fig. 4 that the ammonia coverage of the first active site (weak active site) is reduced rapidly and the ammonia coverage of the second active site (strong active site) is reduced only slightly during the isothermal desorption process. This indicates that during the chemical reaction, the reaction rate of ammonia in the first active site is faster, which plays an important role in catalyzing the entire catalytic reduction reaction.
In one embodiment of the present application, the ammonia adsorption reaction rate raComprises the following steps: r isa＝r1 a+r2 aWherein r is1 aIs the first ammonia adsorption rate, r2 aThe second ammonia adsorption rate.
First ammonia adsorption rate r1 aComprises the following steps: r is1 a＝ka 1CNH3(1-θ1 NH3) Wherein, CNH3Is NH in the gas phase3Volume concentration, ppm; 01 NH3Is NH at the first active site3Surface coverage,%; k is a radical ofa 1Is the adsorption rate factor on the first active site, m3/(mol·s)。
The second ammonia adsorption rate r2 aComprises the following steps: r is2 a＝ka 2CNH3(1-θ2 NH3)，
Wherein, CNH3Is NH in the gas phase3Volume concentration, ppm; theta2 NH3Is NH in the second active site3Surface coverage,%; k is a radical ofa 2Is an adsorption rate factor, m, on the second active site3/(m0l·s)。
In one embodiment of the present application, the ammonia desorption reaction rate rdComprises the following steps: r isd＝r1 d+r2 d. Wherein r is1 dIs the first ammonia desorption rate, r2 dThe second ammonia desorption rate.
First ammonia desorption rate r1 dComprises the following steps: r is1 d＝kd 1exp[(-Ed 1/RT)(1-α1θ1 NH3]θ1 NH3，
Wherein k isd 1Is the first active site ammonia desorption rate factor, S-1；Ed 1Is the first active site ammonia desorption reaction activation energy, kJ/mol; alpha is alpha1A heterogeneity constant corresponding to the first active site; theta1 NH3Is NH at the first active site3Surface coverage,%; r is an ideal gas constant, J/(mol.K); t is the temperature, K.
The second ammonia desorption rate r2 dComprises the following steps: r is2 d＝kd 2exp[(-Ed 2/RT)(1-α1θ2 NH3]θ2 NH3，
Wherein k isd 2Is the second active site ammonia desorption rate factor, S-1；Ed 2The second active site ammonia desorption reaction activation energy is kJ/mol; alpha is alpha2A heterogeneity constant corresponding to the second active site; theta2 NH3Is NH in the second active site3Surface coverage,%; r is an ideal gas constant, J/(mol.K); t is the temperature, K.
In addition, the chemical reactions in the SCR system are standard reactions, fast reactions and slow reactions, and the chemical equation is as follows:
4NH3+4NO+O2→4N2+6H2O
2NH3+NO+NO2→2N2+3H2O
8NH3+6NO2→7N2+12H2O。
the chemical reaction between the nitrogen oxides and ammonia is referred to herein as the nitrogen oxide reaction, and the reaction rate of this reaction is reported as the nitrogen oxide reaction rate.
When the chemical reaction occurs at the first active site of the catalyst, namely the Lewis active site, the corresponding first nitrogen oxide reaction rate R1 NoxComprises the following steps: r1 NOx＝r1 NOxC1 sθ1 NH3. Wherein, r2 NOxIs the first nitrogen oxide reaction rate constant, r2 NOx＝C2sRTKNOxexp(-ENOx/RT)，C2 sAn ammonia storage capacity that is a second active site of the SCR system; eNOxIs the activation energy of the first nitrogen oxide reaction, kJ/mol; kNOxIs a reaction rate factor, S, of the first nitrogen oxide reaction-1；θ2 NH3Ammonia coverage of the second active site,%; r is an ideal gas constant, J/(mol.K); t is the temperature, K.
When the chemical reaction occurs at the second active site of the catalyst, i.e., the Bronsted active site, the corresponding second nitroxide reaction rate R2 NoxComprises the following steps: r2 NOx＝r2 NOxC2 sθ2 NH3，
Wherein r is2 NOxIs a second oxynitride reaction rate constant, r2 NOx＝C2sRTKNOxexp(-ENOx/RT)，C2 sAmmonia storage capacity for the second active site of the SCR system, ENOxIs the second oxynitride reaction activation energy, kJ/mol; kNOxIs a second oxynitride reaction rate factor, S-1；θ2 NH3Ammonia coverage of the second active site,%; r is an ideal gas constant, J/(mol.K); t is the temperature, K.
For double active sites, the reaction rate R of nitrogen oxides in the catalytic reduction reaction process of an SCR systemNOx,Comprises the following steps: rNOx＝R1 NOx+R2 NOx＝RTKNOxexp(-ENOx/RT)(C1 sθ1 NH3+C2 sθ2 NH3)。
The calculation method of the embodiment of the application is based on the double active sites, and different ammonia coverage rates under the double active sites are fully utilized, so that the calculation accuracy of the reaction rate of nitrogen oxides in the SCR reaction physical model at high and low temperatures is higher, the NOx emission control is further improved, and the possibility of OBD misinformation is reduced.
In an SCR system, in addition to the above reaction, there is also an oxidation reaction of ammonia, which is called an ammonia oxidation reaction, and the chemical equation of the reaction is as follows: 4NH3+3Ox→2N2+6H2And O. The ammonia in the reaction equation is also ammonia adsorbed on the surface of the catalyst, i.e., only ammonia in the adsorbed state can undergo an ammoxidation reaction. And the ammonia oxidation reaction has different reaction rates aiming at ammonia at different active sites of the catalyst.
When the ammoxidation reaction occurs at the first active site of the catalyst, i.e., the Lewis active site, the corresponding first ammoxidation rate R1 OxComprises the following steps: r1 Ox＝r1 Oxθ1 NH3。
Wherein r is1 OxComprises the following steps: first ammoxidation rate constant, r1 Ox＝C1 cKOxexp(-EOx/RT)，C1 cAmmonia storage capacity for the first active site of an SCR system, EOxActivation energy for the first ammoxidation reaction, kJ/mol; kOxIs a first ammoxidation rate factor, S-1；θ1 NH3Ammonia coverage of the first active site,%; r is an ideal gas constant, J/(mol.K); t is the temperature, K.
When the ammoxidation reaction occurs at the second active site of the catalyst, i.e., the Bronsted active site, the corresponding second ammoxidation rate R2 OxComprises the following steps: r2 Ox＝r2 Oxθ2 NH3，
Wherein r is2 OxIs the second ammoxidation reaction rate constant, r2 Ox＝C2cKOxexp(-EOx/RT)，C2 cFor ammonia storage capacity of a second active site in the SCR system, EOxActivation energy for the second ammoxidation reaction, kJ/mol; kOxIs a second ammoxidation reaction rate factor, S-1；θ2 NH3Ammonia coverage of the second active site,%; r is an ideal gas constant, J/(mol.K); t is the temperature, K.
Aiming at double active sites, the ammoxidation reaction rate R in the catalytic reduction reaction process of an SCR systemOxComprises the following steps: rOx＝R1 Ox+R2 Ox＝KOxexp(-EOx/RT)(C1 cθ1 NH3+C2 cθ2 NH3)。
The calculation method of the embodiment of the application is based on the double active sites, and different ammonia coverage rates under the double active sites are fully utilized, so that the calculation accuracy of the ammonia oxidation rate in the SCR reaction physical model at high and low temperatures is higher, the NOx emission control is improved, and the possibility of OBD misinformation is reduced.
In order to verify the accuracy of the double-active-site reaction model, the simulation result of the single-active-site reaction model and the simulation result of the double-active-site reaction model are compared with the actual engine test result.
The operation method comprises the following steps: assuming that the same flow of ammonia gas is input to various reaction models and an actual engine, the outlet ammonia volume concentration of the engine under different reaction models is calculated, and the outlet ammonia volume concentration of the actual engine under the same working condition is measured, and the obtained comparison result is shown in fig. 5. In fig. 5, (a) is a comparison chart at 100 ℃, (b) is a comparison chart at 200 ℃, and (c) is a comparison chart at 300 ℃.
As can be seen from (a) to (c) in fig. 5, the simulation result of the dual-active-site reaction model is closer to the actual experimental data at different temperatures, and thus, it can be proved that the working condition applicability and the control robustness of the dual-active-site reaction model are better, the NOx emission control can be improved, and the OBD error rate can be reduced.
Based on the same inventive concept, the application provides a control method of the urea passing amount of the engine, which comprises the following steps: the chemical reaction rate of the SCR system is calculated by using the calculation method, and the introduction amount of the urea is controlled according to the obtained chemical reaction rate.
It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
Claims (10)
1. A method for calculating the chemical reaction rate of an SCR system is characterized by comprising the following steps:
determining a parameter set according to the catalyst; wherein the catalyst comprises a first active site and a second active site, the parameter set comprises a first set of parameters corresponding to a chemical reaction at the first active site and a second set of parameters corresponding to a chemical reaction at the second active site;
determining a first reaction rate based on the first set of parameters and a second reaction rate based on the second set of parameters;
determining a chemical reaction rate of the SCR system based on the first reaction rate and the second reaction rate.
2. The method of claim 1, wherein determining the chemical reaction rate of the SCR system based on the first reaction rate and the second reaction rate comprises:
determining the chemical reaction rate from the sum of the first reaction rate and the second reaction rate.
3. The computing method of claim 1 or 2, wherein the chemical reaction rates comprise an ammonia adsorption reaction rate, an ammonia desorption reaction rate, a nitrogen oxide reaction rate, and an ammonia oxidation reaction rate, wherein the first reaction rate comprises a first ammonia adsorption rate, a first ammonia desorption rate, a first nitrogen oxide reaction rate, and a first ammonia oxidation reaction rate, and wherein the second reaction rate comprises a second ammonia adsorption rate, a second ammonia desorption rate, a second nitrogen oxide reaction rate, and a second ammonia oxidation reaction rate; wherein,
determining the ammonia adsorption reaction rate according to the sum of the first ammonia adsorption rate and the second ammonia adsorption rate;
determining the ammonia desorption reaction rate according to the sum of the first ammonia desorption rate and the second ammonia desorption rate;
determining the nitrogen oxide reaction rate from the sum of the first nitrogen oxide reaction rate and the second nitrogen oxide reaction rate;
determining the ammoxidation reaction rate according to the sum of the first ammoxidation reaction rate and the second ammoxidation reaction rate.
4. The calculation method according to claim 3, wherein the first ammonia adsorption rate r1 aComprises the following steps: r is1 a＝ka 1CNH3(1-θ1 NH3)，
Wherein, CNH3Is NH in the gas phase3Volume concentration; theta1 NH3Is NH at the first active site3Surface coverage; k is a radical ofa 1Is an adsorption rate factor on the first active site;
the second ammonia adsorption rate r2 aComprises the following steps: r is2 a＝ka 2CNH3(1-θ2 NH3)，
Wherein, CNH3Is NH in the gas phase3Volume concentration; theta2 NH3Is NH in the second active site3Surface coverage; k is a radical ofa 2Is an adsorption rate factor on the second active site;
the ammonia adsorption reaction rate raComprises the following steps: r isa＝r1 a+r2 a。
5. The calculation method according to claim 3, wherein the first ammonia desorption rate r1 dComprises the following steps: r is1 d＝kd 1exp[(-Ed 1/RT)(1-α1θ1 NH3]θ1 NH3，
Wherein k isd 1Is a first active site ammonia desorption rate factor, Ed 1Is the first active site ammonia desorption reaction activation energy, alpha1Is the heterogeneity constant, θ, corresponding to the first active site1 NH3Is NH at the first active site3Surface coverage, R is the ideal gas constant, T is the temperature;
the second ammonia desorption rate r2 dComprises the following steps: r is2 d＝kd 2exp[(-Ed 2/RT)(1-α1θ2 NH3]θ2 NH3，
Wherein k isd 2Is a second active site ammonia desorption rate factor, Ed 2Is the second active site ammonia desorption reaction activation energy,α2is a heterogeneity constant, θ, corresponding to the second active site2 NH3Is NH in the second active site3Surface coverage, R is the ideal gas constant, T is the temperature;
the ammonia desorption reaction rate rdComprises the following steps: r isd＝r1 d+r2 d。
6. The calculation method according to claim 3, wherein the first nitrogen oxide reaction rate R1 NoxComprises the following steps: r1 NOx＝r1 NOxC1 sθ1 NH3，
Wherein r is1 NOxIs the first nitrogen oxide reaction rate constant, r1 NOx＝C1sRTKNOxexp(-ENOx/RT)，C1 sAmmonia storage capacity for the first active site of an SCR system, ENOxIs the activation energy of the first nitrogen oxide reaction, KNOxIs the reaction rate factor, θ, of the first nitrogen oxide reaction1 NH3Ammonia coverage of the first active site, R being the ideal gas constant, T being the temperature;
the second oxynitride reaction rate R2 NoxComprises the following steps: r2 NOx＝r2 NOxC2 sθ2 NH3，
Wherein r is2 NOxIs a second oxynitride reaction rate constant, r2 NOx＝C2sRTKNOxexp(-ENOx/RT)，C2 sAmmonia storage capacity for the second active site of the SCR system, ENOxActivation energy for the second nitroxide reaction, KNOxIs the reaction rate factor, theta, of the second nitrous oxide reaction2 NH3Ammonia coverage of the second active site.
7. The calculation method according to claim 6, wherein the nitrogen oxide reaction rate RNOxThe method comprises the following steps:
RNOx＝R1 NOx+R2 NOx＝RTKNOxexp(-ENOx/RT)(C1 sθ1 NH3+C2 sθ2 NH3)。
8. the method of claim 3, wherein the first ammonia oxidation rate R is1 OxComprises the following steps: r1 Ox＝r1 Oxθ1 NH3，
Wherein r is1 OxIs the first ammoxidation rate constant, r1 Ox＝C1 cKOxexp(-EOx/RT)，C1 cAmmonia storage capacity for the first active site of an SCR system, EOxActivation energy of the first ammoxidation reaction, KOxIs a first ammoxidation rate factor, theta1 NH3Ammonia coverage of the first active site, R being the ideal gas constant, T being the temperature;
the second ammoxidation rate R2 OxComprises the following steps: r2 Ox＝r2 Oxθ2 NH3，
Wherein r is2 OxIs the second ammoxidation reaction rate constant, r2 Ox＝C2cKOxexp(-EOx/RT)，C2 cFor ammonia storage capacity of a second active site in the SCR system, EOxActivation energy for the second ammoxidation reaction, KOxIs a second ammoxidation reaction rate factor, θ2 NH3Ammonia coverage of the second active site.
9. The calculation method according to claim 8, wherein the ammoxidation reaction rate ROxComprises the following steps: rOx＝R1 Ox+R2 Ox＝KOxexp(-EOx/RT)(C1 cθ1 NH3+C2 cθ2 NH3)。
10. A control method for the urea introducing amount of an engine is characterized by comprising the following steps:
calculating a chemical reaction rate of the SCR system using the calculation method of any one of claims 1 to 9,
and controlling the introduction amount of the urea according to the obtained chemical reaction rate.
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