CN106837480B

CN106837480B - A model-based urea injection quantity control method and post-treatment control system

Info

Publication number: CN106837480B
Application number: CN201611220483.1A
Authority: CN
Inventors: 张军; 张振涛; 王晓华; 曹庆和; 张瑜
Original assignee: Weichai Power Co Ltd
Current assignee: Weichai Power Co Ltd
Priority date: 2016-12-26
Filing date: 2016-12-26
Publication date: 2019-02-12
Anticipated expiration: 2036-12-26
Also published as: CN106837480A

Abstract

The urea injecting quantity control method based on model that the present invention relates to a kind of, described method includes following steps: S1: according to practical urea injecting quantity, calculating the first ammonia Stored Value in SCRF based on SCRF model；S2: the second ammonia Stored Value in SCR is calculated based on SCR model；S3: the first ammonia Stored Value and the second ammonia Stored Value of S1 step and the acquisition of S2 step are weighted processing and obtain practical ammonia Stored Value；S4: S3 step is obtained into practical ammonia Stored Value and is made the difference with ammonia storage setting value, and passes through PID controller, obtains the ammonia nitrogen ratio of Closed-cycle correction；S5: by the ammonia nitrogen ratio for the Closed-cycle correction that S4 step obtains and feedforward ammonia nitrogen ratio do and, be eventually converted into the urea injecting quantity of demand.The present invention, which uses, is based on model Closed-loop Control Strategy, is able to achieve the accurate control to urea injection, is not only able to satisfy engine emission requirements, and can be reduced staking-out work and solve crystallisation problems.

Description

A kind of urea injecting quantity control method and post-processing control system based on model

Technical field

The present invention relates to engine art, in particular to gas discharges field of purification.

Background technique

With increasingly stringent, band SCR (Selective Catalyst Reduction, the selectivity of automobile emission regulation Catalytic reduction reaction) after-treatment system become reduce exhaust emission mainstream technology.After-treatment system with SCR reduces discharge The method of pollution is achieved the purpose that reduce nitrogen oxides, to reduce discharge, meets row by spraying urea into SCR case Put the requirement of regulation.

On the basis of SCR, SCRF technology is further developed, SCRF, which refers to, is coated in DPF (particulate matter for SCR catalyst Trap) on, also known as SCR on Filter, SDPF etc..Using SCRF technology, it is not only able to lower post-processing volume, Er Qieqi It is more excellent to fire characteristic, can be improved SCR conversion efficiency.SCRF technology equally faces the demand that urea injecting quantity accurately controls.

In the prior art, the method for controlling urea injecting quantity is that calibration is separately controlled using SCR and DPF, in this case, NH in SCR₃With DPF passive regeneration there are it is public and compete consumption NO₂The case where.Therefore the prior art adapts in SCRF system Property is poor, and stated accuracy is difficult to meet demand.

Summary of the invention

The present invention proposes to be able to achieve the accurate control to urea injection using model Closed-loop Control Strategy is based on, not only can Meet engine emission requirements, and can be reduced staking-out work and solve crystallisation problems.

An object of the present invention is achieved through the following technical solutions.

A kind of urea injecting quantity control method based on model, described method includes following steps:

S1: practical urea injecting quantity is inputted into SCRF model, and the first ammonia Stored Value in SCRF is calculated based on SCRF model；

S2: the second ammonia Stored Value in SCR is calculated based on SCR model；

S3: the first ammonia Stored Value and the second ammonia Stored Value of S1 step and the acquisition of S2 step are weighted processing and obtain practical ammonia Stored Value；

S4: S3 step is obtained into practical ammonia Stored Value and is made the difference with ammonia storage setting value, and passes through PID controller, closed loop is obtained and repairs Positive ammonia nitrogen ratio；

S5: by the ammonia nitrogen ratio for the Closed-cycle correction that S4 step obtains and feedforward ammonia nitrogen ratio do and, be eventually converted into the urine of demand Plain the amount of injection.

Further, in S1 step, the input of the SCRF model further includes NH3 concentration, O₂Concentration, NO concentration, NO₂Concentration, Temperature before SCRF, extraction flow and carbon original discharge capacity；The SCRF model is specially that SCRF is radially divided into multiple unit moulds Block calculates separately carbon carrying capacity, ammonia storage, NO, NO according to energy conservation equation and mass-conservation equation in each unit module₂With NH₃；The ammonia storage of each unit is added and obtains the first ammonia Stored Value.

Further, in S2 step, the input of the SCR model includes NH₃Concentration, O₂Concentration, NO concentration, NO₂Concentration and Gas temperature before SCR；The SCR model is specially that SCR is radially divided into multiple unit modules, to each unit module application Energy conservation equation and mass-conservation equation, to calculate the ammonia storage of each unit module, NO, NO₂、NH₃And temperature, to every The ammonia storage of a unit module, which is added, obtains the second ammonia Stored Value.

Further, in S3 step, MAP is looked into according to revolving speed and distributive value and obtains the weighting coefficient progress weighting processing.

Further, the weighting processing obtains practical ammonia Stored Value are as follows: the first ammonia Stored Value and weighting coefficient are done product first, obtained The first ammonia Stored Value after must weighting；Then, it is made the difference with numerical value 2 with weighting coefficient, difference and the second ammonia Stored Value is done into product, added The second ammonia Stored Value after power；Finally, by after weighting the first ammonia Stored Value and weighting after the second ammonia Stored Value do and, obtain practical ammonia Stored Value.

Further, pass through the NO of calibration DOC₂Transformation efficiency (such as being demarcated according to revolving speed and distributive value) obtains NO₂Then proportion MAP looks into the MAP by revolving speed and distributive value and obtains NO₂Proportion, by NO in engine original row_x Concentration and the NO₂Proportion does product and obtains the NO for inputting the SCRF model₂Concentration, then by original row in NO_xConcentration and NO₂ Concentration makes the difference the NO concentration for obtaining and inputting the SCRF model.

Further, temperature before SCRF is obtained according to temperature sensor；According to practical urea injecting quantity (such as by its divided by 5.429) NH before SCRF is obtained₃Concentration；Extraction flow is obtained according to air inflow and distributive value；O₂Concentration is by NO_xSensor measurement It obtains.

Further, by NH in SCRF₃Absorption and NH₃The chemical reaction rate of desorption is set as calibrable variable, and the variable is logical Summary test data is crossed to be demarcated.

Further, the ammonia storage setting value in the S4 step and the feedforward ammonia nitrogen ratio in S5 step are According to SCRF temperature and air speed, it is determined by inquiring the corresponding MAP demarcated in advance.

Another object of the present invention provides a kind of After-treatment technics control system, can be real by following technical solution It is existing.

A kind of After-treatment technics control system, the post-processing control system includes the DOC system being sequentially arranged, SCRF System, SCR system and ASC system are disposed with upstream NO before the DOC system_xSensor and DOC upstream temperature sensor, Urea nozzle and SCRF upstream temperature sensor are disposed between DOC system and SCRF system；SCRF system and SCR system it Between be disposed with SCR upstream temperature sensor, and there also is provided downstream NO after ASC_xSensor and SCR downstream temperature sensing Device, the post-processing control system control urea injecting quantity using the above-mentioned urea injecting quantity control method based on model System.

The present invention has the advantages that

The present invention is based on SCRF hardware system, the Closed-loop Control Strategy based on the storage of double ammonia is extracted, realizes and urea is sprayed Accurate control, not only can guarantee discharge meet demand, and System design based on model is adaptable, calibration is simple, only need to be from Line calibration, it is versatile, be conducive to commercialization.

Detailed description of the invention

By reading the following detailed description of the preferred embodiment, various other advantages and benefits are common for this field Technical staff will become clear.The drawings are only for the purpose of illustrating a preferred embodiment, and is not considered as to the present invention Limitation.And throughout the drawings, the same reference numbers will be used to refer to the same parts.In the accompanying drawings:

Fig. 1 shows the After-treatment technics control system component layout figure of embodiment according to the present invention.

Fig. 2 shows the urea injecting quantity control method urea injection control logic charts based on model.

Specific embodiment

The illustrative embodiments of the disclosure are more fully described below with reference to accompanying drawings.Although showing this public affairs in attached drawing The illustrative embodiments opened, it being understood, however, that may be realized in various forms the disclosure without the reality that should be illustrated here The mode of applying is limited.It is to be able to thoroughly understand the disclosure on the contrary, providing these embodiments, and can be by this public affairs The range opened is fully disclosed to those skilled in the art.

Embodiment according to the present invention, after proposing a kind of urea injecting quantity control method based on model and engine Manage control system, with reference to Fig. 1, the post-processing control system include the DOC system being sequentially arranged, SCRF system, SCR system and ASC system is disposed with upstream NO before the DOC system_xSensor and DOC upstream temperature sensor, in DOC system and SCRF system Urea nozzle and SCRF upstream temperature sensor are disposed between system；The upstream SCR is disposed between SCRF system and SCR system Temperature sensor, and there also is provided downstream NO after ASC_xSensor and SCR downstream temperature sensor.

With reference to Fig. 2, it is based on above-mentioned arrangement, embodiments of the present invention realize a kind of urea injecting quantity based on model Control method, described method includes following steps:

S1: practical urea injecting quantity is inputted into SCRF model, and the first ammonia Stored Value in SCRF is calculated based on SCRF model θ₁；

S2: the second ammonia Stored Value θ in SCR is calculated based on SCR model₂；

S3: the first ammonia Stored Value θ that S1 step and S2 step are obtained₁With the second ammonia Stored Value θ₂Processing is weighted to obtain in fact Border ammonia Stored Value θ；

In the above-mentioned methods:

For S1 step, the input of the SCRF model further includes NH3 concentration, O₂Concentration, NO concentration, NO₂Concentration, SCRF Preceding temperature, extraction flow and carbon original discharge capacity；The SCRF model is specially that SCRF is radially divided into multiple unit modules, Carbon carrying capacity, ammonia storage, NO, NO are calculated separately according to energy conservation equation and mass-conservation equation in each unit module₂And NH₃；It is right The ammonia storage of each unit, which is added, obtains the first ammonia Stored Value.Due in SCRF, carbon distribution number ammonia can be stored up and generate certain influence, Therefore it needs NH in SCRF₃Absorption and NH₃The chemical reaction rate of desorption is set as calibrable variable, and variable needs pass through Test data is summarized to be demarcated.Wherein, pass through the NO of calibration DOC₂Transformation efficiency obtains NO₂Proportion MAP, then passes through Revolving speed and distributive value look into the MAP and obtain NO₂Proportion, by NOx concentration and the NO in engine original row₂Proportion is done Product obtains the NO for inputting the SCRF model₂Concentration, then by original row in NO_xConcentration and NO₂Concentration makes the difference acquisition and inputs the SCRF The NO concentration of model.Temperature before SCRF is obtained according to temperature sensor；According to practical urea injecting quantity, by it divided by numerical value 5.429, Obtain NH before SCRF₃Concentration；Extraction flow is obtained according to air inflow and distributive value；O₂Concentration is by NO_xSensor measurement obtains.

For S2 step, the input of the SCR model includes NH₃Concentration, O₂Concentration, NO concentration, NO₂Gas before concentration and SCR Temperature；The SCR model is specially that SCR is radially divided into multiple unit modules, is kept each unit module applied energy Permanent equation and mass-conservation equation, to calculate the ammonia storage of each unit module, NO, NO₂、NH₃And temperature, to each unit The ammonia storage of module, which is added, obtains the second ammonia Stored Value.

For S3 step, MAP is looked into according to revolving speed and distributive value and obtains the weighting coefficient progress weighting processing.Specifically: The first ammonia Stored Value and weighting coefficient are done into product first, the first ammonia Stored Value after being weighted；Then, with numerical value 2 and weighting coefficient It makes the difference, difference and the second ammonia Stored Value is done into product, the second ammonia Stored Value after being weighted；Finally, by the first ammonia Stored Value after weighting Done with the second ammonia Stored Value after weighting and, obtain practical ammonia Stored Value.

For the ammonia storage setting value in the S4 step and the feedforward ammonia nitrogen ratio in S5 step, according to equal SCRF temperature and air speed are determined by inquiring the corresponding MAP demarcated in advance.

The foregoing is only a preferred embodiment of the present invention, but scope of protection of the present invention is not limited thereto, In the technical scope disclosed by the present invention, any changes or substitutions that can be easily thought of by anyone skilled in the art, It should be covered by the protection scope of the present invention.Therefore, protection scope of the present invention should be with the protection model of the claim Subject to enclosing.

Claims

1. a model-based urea injection quantity control method, is characterized in that, described method comprises the steps:

S1: Input the actual urea injection amount into the SCRF model, and calculate the first ammonia storage value in the SCRF based on the SCRF model;

S2: Calculate the second ammonia storage value in the SCR based on the SCR model;

S3: weighting the first ammonia storage value and the second ammonia storage value obtained in steps S1 and S2 to obtain an actual ammonia storage value;

S4: make the difference between the actual ammonia storage value obtained in step S3 and the ammonia storage set value, and obtain the closed-loop corrected ammonia-nitrogen ratio through the PID controller;

S5: The closed-loop corrected ammonia-nitrogen ratio obtained in step S4 is summed with the feed-forward ammonia-nitrogen ratio, and finally converted into the required urea injection amount.

2. The model-based urea injection quantity control method according to claim 1, wherein in step S1, the input of the SCRF model further includes NH3 concentration, _O2 concentration, NO concentration, NO2 concentration, pre _- SCRF concentration temperature, exhaust flow and carbon emission; the SCRF model is specifically divided into multiple unit modules radially, and in each unit module, the carbon load and ammonia storage are calculated respectively according to the energy conservation equation and the mass conservation equation. , NO, NO ₂ and NH ₃ ; the first ammonia storage value is obtained by adding the ammonia storage for each unit.

3. The model-based urea injection quantity control method according to claim 1, wherein in step S2, the input of the SCR model includes _NH3 concentration, _O2 concentration, NO concentration, NO2 concentration and pre _- SCR gas temperature; the SCR model specifically divides the SCR radially into multiple unit modules, and applies the energy conservation equation and mass conservation equation to each unit module, so as to calculate the ammonia storage, NO, NO ₂ of each unit module , NH ₃ and temperature, add the ammonia storage for each unit module to obtain the second ammonia storage value.

4 . The model-based urea injection quantity control method according to claim 1 , wherein, in step S3 , the weighting process is performed by checking the MAP according to the rotational speed and the fuel injection quantity to obtain a weighting coefficient. 5 .

5. The model-based urea injection quantity control method as claimed in claim 4, wherein the weighted process obtains the actual ammonia storage value: first, the first ammonia storage value and the weighting coefficient are multiplied to obtain the weighted The first ammonia storage value; then, use the numerical value 2 and the weighting coefficient to make a difference, and multiply the difference and the second ammonia storage value to obtain the weighted second ammonia storage value; finally, the weighted first ammonia storage value The actual ammonia storage value is obtained by summing with the weighted second ammonia storage value.

6. The model-based urea injection quantity control method according to claim 2, characterized in that, by calibrating the NO ₂ conversion efficiency of DOC, the NO ₂ proportion MAP is obtained, and then the MAP is checked by the rotational speed and the fuel injection quantity. Obtain the proportion of NO ₂ , take the product of the NO _x concentration in the original exhaust of the engine and the proportion of the NO ₂ to obtain the NO ₂ concentration input into the SCRF model, and then make the difference between the NO _x concentration in the original exhaust and the NO ₂ concentration Obtain the NO concentration input to the SCRF model.

7. The model-based urea injection quantity control method as claimed in claim 2, wherein the temperature before SCRF is obtained according to the temperature sensor _; the concentration of NH before SCRF is obtained according to the actual urea injection quantity; The amount of exhaust gas flow; _O2 concentration is measured by the _NOx sensor.

8. The model-based urea injection quantity control method according to claim ₂ , wherein the chemical reaction rates _of NH adsorption and NH desorption in the SCRF are set as a calibratable variable, which is determined by summarizing experimental data. Calibration.

9. The model-based urea injection quantity control method according to any one of claims 1 to 8, wherein the ammonia storage set value in the step S4 and the feedforward ammonia nitrogen in the step S5 The ratio is determined by querying the corresponding MAP calibrated in advance according to the SCRF temperature and airspeed.

10. An engine aftertreatment control system, the aftertreatment control system comprising a DOC system, a SCRF system, an SCR system and an ASC system arranged in sequence, an upstream _NOx sensor and a DOC upstream temperature sensor are arranged in front of the DOC system, The urea nozzle and the SCRF upstream temperature sensor are arranged between the DOC system and the SCRF system; the SCR upstream temperature sensor is arranged between the SCRF system and the SCR system, and the downstream _NOx sensor and the SCR downstream temperature sensor are also arranged after the ASC, so The aftertreatment control system uses the model-based urea injection quantity control method according to any one of claims 1 to 9 to control the urea injection quantity.