CN104314650A - SCR (selective catalytic reduction) feed-forward control method and device - Google Patents

Abstract

The invention discloses an SCR (selective catalytic reduction) feed-forward control method and device. The SCR feed-forward control method comprises the following steps: acquiring SCR upstream temperature, the NOx emission of an engine, exhaust gas mass flow and urea spraying rate in real time; calculating an actual average ammonia storage concentration value according to the SCR upstream temperature, the NOx emission of the engine, the exhaust gas mass flow and the urea spraying rate; generating a regulation value for regulating the urea spraying rate according to a preset urea spraying regulation algorithm by taking a difference between a set average ammonia storage concentration value and the actual average ammonia storage concentration value as a parameter. According to the method and the device, required urea spraying rate can be calculated in real time according to a current working condition of the engine without waiting for the variation of residual NH3 at the rear end of an SCR catalytic converter; the lag of regulation of the urea spraying rate for the variation of the residual NH3 is avoided, so that the transient control effect is better, and the leakage of NH3 can be effectively avoided.

Description

A kind of SCR feed forward control method and device

Technical field

The present invention relates to vent gas treatment field, particularly relate to a kind of SCR feed forward control method and device.

Background technique

In the main noxious emission of diesel engine, comprise nitrous oxide and nitrogen dioxide, nitrous oxide and nitrogen dioxide can be referred to as NOx.

Control, in noxious gas emission technology, to include SCR (Selective Catalytic Reduction, selective catalytic reduction technology); Its principle is, in containing the tail gas of NOx, spray into urea, the NOx in tail gas and ammonia (NH3) is reacted and is reduced into N2 (nitrogen) and water, and then reaches the object controlling exhaust emissions harmful gas.

In SCR technology, the control of urea injecting quantity is key technology, and the emitted dose of urea needs according to the real-time adjustment of the discharge amount of NOx; If urea injecting quantity is very few, effectively can not be reacted by NOx and being reduced into N2 (nitrogen) and water, be that residual NOx is too much; If urea injecting quantity is too much, then can causes more residue NH3, cause NH3 to reveal.

In prior art, the control of urea injecting quantity is generally realized by default input-output mappings table (MAP), concrete, the data information remaining NH3 is obtained in exhausting air by the exhaust gas sensor being located at SCR catalytic converter rear end, and with this data information for parameter, calculated the controlled quentity controlled variable generating urea injecting quantity by specific algorithm.

Inventor finds through research, technological scheme of the prior art, the data information of the residue NH3 that the controlled quentity controlled variable needs generating urea injecting quantity feed back with exhaust gas sensor is for parameter, that is, in the controlled quentity controlled variable and exhausting air of current urea injecting quantity, only remain NH3 inadaptable, just can carry out the controlled quentity controlled variable adjustment of follow-up urea injecting quantity, like this, due to stagnant after the controlled quentity controlled variable adjustment of urea injecting quantity, so transient control effect is poor, NH3 is easily caused to reveal.

Summary of the invention

Technical problem to be solved by this invention effectively avoids the leakage of NH3, provides a kind of SCR feed forward control method, comprising:

Obtain real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity;

Average storage ammonia density actual value is calculated according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity;

On average to store up the difference of ammonia density setting value and described average storage ammonia density actual value for parameter, generate the adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

Preferably, in embodiments of the present invention, described calculating according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity on average stores up ammonia density actual value, comprising:

Pass through $C_{{\mathrm{NO}}_x}=\frac{N_1{n}_{{\mathrm{NO}}_x}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_6\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}},$ $C_{{\mathrm{NH}}_3}=\frac{N_1{n}_{{\mathrm{NH}}_3}+N_5\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})},$ $C_s{\stackrel{\·}{\mathrm{\θ}}}_{{\mathrm{NH}}_3}=N_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})C_{{\mathrm{NH}}_3}-[N_5\left(T\right)+N_6\left(T\right)C_{{\mathrm{NO}}_x}+N_7\left(T\right)]{\mathrm{\θ}}_{{\mathrm{NH}}_3}$ With, these four formula are combined and are solved, and obtain average storage ammonia density actual value;

In formula, N ₀, N ₁, N ₂, N ₃for constant, N ₄(T), N ₅(T), N ₆(T), N ₇(T) be temperature variant amount, C _sfor the concentration (mol/m3) of active atomic, for the concentration (mol/m3) of NOx in SCR, for the concentration (mol/m3) of NH3 in SCR, T is SCR inside temperature; Four inputs of SCR physical model comprise: T _infor SCR upstream temperature (K), m _eGfor exhaust air mass flow (kg/s), for the original NOx concentration of motor (mol/s), for the concentration (mol/s) of the NH3 of urea injecting quantity hydrolysis correspondence; An output of SCR physical model is: represent and on average store up ammonia density.

Preferably, in embodiments of the present invention, described urea-spray adjustment algorithm, comprising:

Generate the ratio of described difference and described average storage ammonia density setting value;

With the integral result of described difference for the integral algorithm CMOS macro cell of parameter through presetting;

Urea-spray adjustment amount is generated according to described ratio and described integral result.

Another side in this application, additionally provides a kind of SCR feedforward control device, comprising:

Real-time parameter acquiring unit, for obtaining real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity;

Average storage ammonia density actual value acquiring unit, with calculating average storage ammonia density actual value according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity;

Adjusted value acquiring unit, for the difference of on average storing up ammonia density setting value and described average storage ammonia density actual value for parameter, generate adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

Preferably, in embodiments of the present invention, described average storage ammonia density actual value acquiring unit, comprising:

Pass through $C_{{\mathrm{NO}}_x}=\frac{N_1{n}_{{\mathrm{NO}}_x}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_6\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}},$ $C_{{\mathrm{NH}}_3}=\frac{N_1{n}_{{\mathrm{NH}}_3}+N_5\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})},$ $C_s{\stackrel{\·}{\mathrm{\θ}}}_{{\mathrm{NH}}_3}=N_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})C_{{\mathrm{NH}}_3}-[N_5\left(T\right)+N_6\left(T\right)C_{{\mathrm{NO}}_x}+N_7\left(T\right)]{\mathrm{\θ}}_{{\mathrm{NH}}_3}$ With, these four formula are combined and are solved, and obtain average storage ammonia density actual value;

In formula, N ₀, N ₁, N ₂, N ₃for constant, N ₄(T), N ₅(T), N ₆(T), N ₇(T) be temperature variant amount, C _sfor the concentration (mol/m3) of active atomic, for the concentration (mol/m3) of NOx in SCR, for the concentration (mol/m3) of NH3 in SCR, T is SCR inside temperature; Four inputs of SCR physical model comprise: T _infor SCR upstream temperature (K), m _eGfor exhaust air mass flow (kg/s), for the original NOx concentration of motor (mol/s), for the concentration (mol/s) of the NH3 of urea injecting quantity hydrolysis correspondence; An output of SCR physical model is: represent and on average store up ammonia density.

Preferably, in embodiments of the present invention, described adjusted value acquiring unit, comprises pi controller:

Described pi controller is used for:

Generate the ratio of described difference and described average storage ammonia density setting value;

With the integral result of described difference for the integral algorithm CMOS macro cell of parameter through presetting;

Urea-spray adjustment amount is generated according to described ratio and described integral result.

As can be seen from above-mentioned technological scheme, in this application, calculating average storage ammonia density actual value by the discharge amount of the SCR upstream temperature of Real-time Obtaining, motor NOx, exhaust air mass flow and urea injecting quantity, then obtaining the adjusted value of urea injecting quantity by average storing up ammonia density setting value and the difference of on average storing up ammonia density actual value; By the technological scheme in the application, can be real-time extrapolate required urea injecting quantity according to the current working of motor, so adjust the emitted dose of urea after the residue NH3 change of SCR catalytic converter rear end need not be waited for again, namely, because the adjustment of the urea injecting quantity in the application can not be delayed for residue NH3 change, thus make transient control effect more excellent, effectively can avoid the leakage of NH3.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present application or technological scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, the accompanying drawing that the following describes is only some embodiments recorded in the application, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is the schematic flow sheet of the feed forward control method of SCR described in the application;

Fig. 2 is the structural representation of the feedforward control device of SCR described in the application.

Embodiment

The present invention program is understood better in order to make those skilled in the art person, below in conjunction with the accompanying drawing in the embodiment of the present invention, technological scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.

In order to the technical problem that in prior art, transient control effect is poor can be solved, provide a kind of SCR feed forward control method in this application, as shown in Figure 1, comprise step:

S11, obtain real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity;

In this application, the invention thinking of core is, by Chemical Kinetics, mass conservation law and law of conservation of energy, the actual value of the average storage ammonia density of motor is calculated (comprising: the discharge amount of SCR upstream temperature, motor NOx, exhaust air mass flow and urea injecting quantity) according to the real-time working condition parameter of motor, then more on average store up ammonia density actual value and on average store up ammonia density setting value, thus judge that it is too high or too low for more on average storing up ammonia density actual value, and then adjust accordingly.

Based on above invention thinking, the SCR upstream temperature that the application needs acquisition real-time, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity.

Concrete, in actual applications, SCR upstream temperature can be obtained by upstream temperature sensor; The discharge amount of motor NOx can be obtained by upstream NOx sensor or directly table look-up acquisition according to operating mode; Exhaust air mass flow can obtain exhaust air mass flow by the reduced value of charge-air mass flow sensor+fuel injection quantity; Urea injecting quantity directly leads back can obtain by exporting.

S12, discharge amount, exhaust air mass flow and urea injecting quantity according to SCR upstream temperature, motor NOx calculate average storage ammonia density actual value;

The principle of SCR is spray into urea in containing the tail gas of NOx, the ammonia (NH of urea and water ₃) make the ammonia (NH of NOx in tail gas and urea and water ₃) reaction is reduced into N2 (nitrogen) and water, and then reaches the object controlling exhaust emissions harmful gas, wherein, concrete chemical reaction process comprises:

1, (NH ₂) ₂cO+H ₂o → 2NH ₃+ CO ₂, that is, urea and water react and obtain ammonia (NH ₃);

2, NH ₃(absorption) ← → NH ₃(absorption), namely non-adsorb ammonia is converted into adsorb ammonia;

3, NH ₃(absorption)+NO _x+ O ₂→ N ₂+ H ₂namely O, by the nitrous oxide in ammonia and oxygen and tail gas and nitrogen dioxide chemical reaction, generates harmless nitrogen and water;

4, NH ₃(absorption)+O ₂→ N ₂+ H ₂o, in addition, also has part ammonia and oxygen chemical reaction and generates nitrogen and water.

Due in above-mentioned each step chemical reaction process, Chemical Kinetics, mass conservation law and law of conservation of energy can be followed, therefore, average storage ammonia density actual value can be calculated according to the discharge amount of SCR upstream temperature, motor NOx, exhaust air mass flow and urea injecting quantity, such as, can be specifically combined by following formula to solve, to obtain average storage ammonia density actual value:

$C_{{\mathrm{NO}}_x}=\frac{N_1{n}_{{\mathrm{NO}}_x}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_6\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}},$ $C_{{\mathrm{NH}}_3}=\frac{N_1{n}_{{\mathrm{NH}}_3}+N_5\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})},$ $C_s{\stackrel{\·}{\mathrm{\θ}}}_{{\mathrm{NH}}_3}=N_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})C_{{\mathrm{NH}}_3}-[N_5\left(T\right)+N_6\left(T\right)C_{{\mathrm{NO}}_x}+N_7\left(T\right)]{\mathrm{\θ}}_{{\mathrm{NH}}_3},$ With,

In above-mentioned formula:

In formula, N ₀, N ₁, N ₂, N ₃for constant, N ₄(T), N ₅(T), N ₆(T), N ₇(T) be temperature variant amount, C _sfor the concentration (mol/m3) of active atomic, for the concentration (mol/m3) of NOx in SCR, for the concentration (mol/m3) of NH3 in SCR, T is SCR inside temperature; Four inputs of SCR physical model comprise: T _infor SCR upstream temperature (K), m _eGfor exhaust air mass flow (kg/s), for the original NOx concentration of motor (mol/s), for the NH that urea injecting quantity hydrolysis is corresponding ₃concentration (mol/s); An output of SCR physical model is: represent and on average store up ammonia density.

S13, on average to store up ammonia density setting value and on average store up the difference of ammonia density actual value for parameter, according to the adjusted value of default urea-spray adjustment algorithm generation for adjusting described urea injecting quantity.

Owing to passing through step S12, real-time average storage ammonia density actual value can be obtained, like this, next just ammonia density setting value will can on average be stored up and real-time average storage ammonia density actual value carries out mathematic interpolation, thus current average storage ammonia density actual value can be learnt and on average store up compared with ammonia density setting value, actually or excessive not enough; And then the difference by calculating, generate the adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

In actual applications, urea-spray adjustment algorithm specifically can be passed through pi controller (proportion adjustment and integral adjustment controller, proportional integral controller) and realize, concrete, on the one hand, difference and the ratio on average storing up ammonia density setting value is generated; On the other hand, with difference be also the integral result of parameter through default integral algorithm CMOS macro cell; Then, urea-spray adjustment amount is generated according to ratio and integral result.

In sum, in this application, calculating average storage ammonia density actual value by the discharge amount of the SCR upstream temperature of Real-time Obtaining, motor NOx, exhaust air mass flow and urea injecting quantity, then obtaining the adjusted value of urea injecting quantity by average storing up ammonia density setting value and the difference of on average storing up ammonia density actual value; By the technological scheme in the application, can be real-time extrapolate required urea injecting quantity according to the current working of motor, so adjust the emitted dose of urea after the residue NH3 change of SCR catalytic converter rear end need not be waited for again, namely, because the adjustment of the urea injecting quantity in the application can not be delayed for residue NH3 change, thus make transient control effect more excellent, effectively can avoid the leakage of NH3.

Another side in this application, additionally provides a kind of SCR feedforward control device, as shown in Figure 2, comprising:

Real-time parameter acquiring unit 01, for obtaining real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity;

Average storage ammonia density actual value acquiring unit 02, with calculating average storage ammonia density actual value according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity;

Adjusted value acquiring unit 03, for the difference of on average storing up ammonia density setting value and described average storage ammonia density actual value for parameter, generate adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

In this application, the invention thinking of core is, by Chemical Kinetics, mass conservation law and law of conservation of energy, the actual value of the average storage ammonia density of motor is calculated (comprising: the discharge amount of SCR upstream temperature, motor NOx, exhaust air mass flow and urea injecting quantity) according to the real-time working condition parameter of motor, then more on average store up ammonia density actual value and on average store up ammonia density setting value, thus judge that it is too high or too low for more on average storing up ammonia density actual value, and then adjust accordingly.

Based on above invention thinking, the application needs to obtain real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity by real-time parameter acquiring unit 01.

Concrete, in actual applications, SCR upstream temperature can be obtained by upstream temperature sensor; The discharge amount of motor NOx can be obtained by upstream NOx sensor or directly table look-up acquisition according to operating mode; Exhaust air mass flow can obtain exhaust air mass flow by the reduced value of charge-air mass flow sensor+fuel injection quantity; Urea injecting quantity directly leads back can obtain by exporting.

Then, average storage ammonia density actual value acquiring unit 02 calculates according to the discharge amount of SCR upstream temperature, motor NOx, exhaust air mass flow and urea injecting quantity;

The principle of SCR is spray into urea in containing the tail gas of NOx, the ammonia (NH of urea and water ₃) make the ammonia (NH of NOx in tail gas and urea and water ₃) reaction is reduced into N2 (nitrogen) and water, and then reaches the object controlling exhaust emissions harmful gas, wherein, concrete chemical reaction process comprises:

1, (NH ₂) ₂cO+H ₂o → 2NH ₃+ CO ₂, that is, urea and water react and obtain ammonia (NH ₃);

2, NH ₃(absorption) ← → NH ₃(absorption), that is, non-adsorb ammonia is converted into adsorb ammonia;

3, NH ₃(absorption)+NO _x+ O ₂→ N ₂+ H ₂o, that is, by the nitrous oxide in ammonia and oxygen and tail gas and nitrogen dioxide chemical reaction, generate harmless nitrogen and water;

4, NH ₃(absorption)+O ₂→ N ₂+ H ₂o, in addition, also has part ammonia and oxygen chemical reaction and generates nitrogen and water.

Due in above-mentioned each step chemical reaction process, Chemical Kinetics, mass conservation law and law of conservation of energy can be followed, therefore, average storage ammonia density actual value can be calculated according to the discharge amount of SCR upstream temperature, motor NOx, exhaust air mass flow and urea injecting quantity, such as, average storage ammonia density actual value acquiring unit 02 can be specifically combined by following formula to solve, to obtain average storage ammonia density actual value:

S21、 $C_{{\mathrm{NO}}_x}=\frac{N_1{n}_{{\mathrm{NO}}_x}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_6\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}};$

S22、 $C_{{\mathrm{NH}}_3}=\frac{N_1{n}_{{\mathrm{NH}}_3}+N_5\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})};$

S23、 $C_s{\stackrel{\·}{\mathrm{\θ}}}_{{\mathrm{NH}}_3}=N_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})C_{{\mathrm{NH}}_3}-[N_5\left(T\right)+N_6\left(T\right)C_{{\mathrm{NO}}_x}+N_7\left(T\right)]{\mathrm{\θ}}_{{\mathrm{NH}}_3};$

S24、 $\stackrel{\·}{T}=N_2{m}_{\mathrm{EG}}(T_{\mathrm{in}}-T)-N_3(T^4-T_{\mathrm{amb}}^4).$

Wherein:

N ₀, N ₁, N ₂, N ₃for constant, N ₄(T), N ₅(T), N ₆(T), N ₇(T) be temperature variant amount, C _sfor the concentration (mol/m3) of active atomic, for the concentration (mol/m3) of NOx in SCR, for the concentration (mol/m3) of NH3 in SCR, T is SCR inside temperature; Four inputs of SCR physical model comprise: T _infor SCR upstream temperature (K), m _eGfor exhaust air mass flow (kg/s), for the original NOx concentration of motor (mol/s), for the concentration (mol/s) of the NH3 of urea injecting quantity hydrolysis correspondence; An output of SCR physical model is: represent and on average store up ammonia density.

Adjusted value acquiring unit 03, on average to store up ammonia density setting value and on average to store up the difference of ammonia density actual value for parameter, generates the adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

Owing to storing up ammonia density actual value acquiring unit 02 by average, real-time average storage ammonia density actual value can be obtained, like this, next just ammonia density setting value will can on average be stored up and real-time average storage ammonia density actual value carries out mathematic interpolation, thus current average storage ammonia density actual value can be learnt and on average store up compared with ammonia density setting value, actually or excessive not enough; And then the difference by calculating, generate the adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

In actual applications, adjusted value acquiring unit 03 specifically can be passed through pi controller (proportion adjustment and integral adjustment controller, proportional integral controller) and realize, concrete, on the one hand, difference and the ratio on average storing up ammonia density setting value is generated; On the other hand, with difference be also the integral result of parameter through default integral algorithm CMOS macro cell; Then, urea-spray adjustment amount is generated according to ratio and integral result.

In sum, in this application, calculating average storage ammonia density actual value by the discharge amount of the SCR upstream temperature of Real-time Obtaining, motor NOx, exhaust air mass flow and urea injecting quantity, then obtaining the adjusted value of urea injecting quantity by average storing up ammonia density setting value and the difference of on average storing up ammonia density actual value; By the technological scheme in the application, can be real-time extrapolate required urea injecting quantity according to the current working of motor, so the residue NH of SCR catalytic converter rear end need not be waited for ₃the emitted dose of urea is adjusted again, that is, because the adjustment of the urea injecting quantity in the application is for residue NH after change ₃change can not be delayed, thus make transient control effect more excellent, effectively can avoid NH ₃leakage.

In this specification, each embodiment adopts the mode of going forward one by one to describe, and what each embodiment stressed is the difference with other embodiments, between each embodiment identical similar portion mutually see.For the device that embodiment provides, the method provided due to itself and embodiment is corresponding, so description is fairly simple, relevant part illustrates see method part.

To the above-mentioned explanation of provided embodiment, professional and technical personnel in the field are realized or uses the present invention.To be apparent for those skilled in the art to the multiple amendment of these embodiments, General Principle as defined herein can without departing from the spirit or scope of the present invention, realize in other embodiments.Therefore, the present invention can not be restricted to these embodiments shown in this article, but will meet the widest scope consistent with principle provided in this article and features of novelty.

Claims (6)

1. a SCR feed forward control method, is characterized in that, comprising:

Obtain real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity;

Average storage ammonia density actual value is calculated according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity;

On average to store up the difference of ammonia density setting value and described average storage ammonia density actual value for parameter, generate the adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

2. SCR feed forward control method according to claim 1, is characterized in that, describedly calculates average storage ammonia density actual value according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity, comprising:

Pass through $C_{{\mathrm{NO}}_x}=\frac{N_1{n}_{{\mathrm{NO}}_x}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_6\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}},$ $C_{{\mathrm{NH}}_3}=\frac{N_1{n}_{{\mathrm{NH}}_3}+N_5\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})},$ $C_s{\stackrel{\·}{\mathrm{\θ}}}_{{\mathrm{NH}}_3}=N_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})C_{{\mathrm{NH}}_3}-[N_5\left(T\right)+N_6\left(T\right)C_{{\mathrm{NO}}_x}+N_7\left(T\right)]{\mathrm{\θ}}_{{\mathrm{NH}}_3}$ With, these four formula are combined and are solved, and obtain average storage ammonia density actual value;

In formula, N ₀, N ₁, N ₂, N ₃for constant, N ₄(T), N ₅(T), N ₆(T), N ₇(T) be temperature variant amount, C _sfor the concentration (mol/m3) of active atomic, for the concentration (mol/m3) of NOx in SCR, for the concentration (mol/m3) of NH3 in SCR, T is SCR inside temperature; Four inputs of SCR physical model comprise: T _infor SCR upstream temperature (K), m _eGfor exhaust air mass flow (kg/s), for the original NOx concentration of motor (mol/s), for the concentration (mol/s) of the NH3 of urea injecting quantity hydrolysis correspondence; An output of SCR physical model is: represent and on average store up ammonia density.

3. SCR feed forward control method according to claim 2, it is characterized in that, described urea-spray adjustment algorithm, comprising:

Generate the ratio of described difference and described average storage ammonia density setting value;

With the integral result of described difference for the integral algorithm CMOS macro cell of parameter through presetting;

Urea-spray adjustment amount is generated according to described ratio and described integral result.

4. a SCR feedforward control device, is characterized in that, comprising:

Real-time parameter acquiring unit, for obtaining real-time SCR upstream temperature, the discharge amount of motor NOx, exhaust air mass flow and urea injecting quantity;

Average storage ammonia density actual value acquiring unit, with calculating average storage ammonia density actual value according to described SCR upstream temperature, the discharge amount of described motor NOx, described exhaust air mass flow and described urea injecting quantity;

Adjusted value acquiring unit, for the difference of on average storing up ammonia density setting value and described average storage ammonia density actual value for parameter, generate adjusted value for adjusting described urea injecting quantity according to the urea-spray adjustment algorithm preset.

5. SCR feedforward control device according to claim 4, it is characterized in that, described average storage ammonia density actual value acquiring unit, comprising:

Pass through $C_{{\mathrm{NO}}_x}=\frac{N_1{n}_{{\mathrm{NO}}_x}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_6\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}},$ $C_{{\mathrm{NH}}_3}=\frac{N_1{n}_{{\mathrm{NH}}_3}+N_5\left(T\right){\mathrm{\θ}}_{{\mathrm{NH}}_3}}{N_0{N}_1{m}_{\mathrm{EG}}T{+N}_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})},$ $C_s{\stackrel{\·}{\mathrm{\θ}}}_{{\mathrm{NH}}_3}=N_4\left(T\right)(1-{\mathrm{\θ}}_{{\mathrm{NH}}_3})C_{{\mathrm{NH}}_3}-[N_5\left(T\right)+N_6\left(T\right)C_{{\mathrm{NO}}_x}+N_7\left(T\right)]{\mathrm{\θ}}_{{\mathrm{NH}}_3}$ With, these four formula are combined and are solved, and obtain average storage ammonia density actual value;

In formula, N ₀, N ₁, N ₂, N ₃for constant, N ₄(T), N ₅(T), N ₆(T), N ₇(T) be temperature variant amount, C _sfor the concentration (mol/m3) of active atomic, for the concentration (mol/m3) of NOx in SCR, for the concentration (mol/m3) of NH3 in SCR, T is SCR inside temperature; Four inputs of SCR physical model comprise: T _infor SCR upstream temperature (K), m _eGfor exhaust air mass flow (kg/s), for the original NOx concentration of motor (mol/s), for the concentration (mol/s) of the NH3 of urea injecting quantity hydrolysis correspondence; An output of SCR physical model is: represent and on average store up ammonia density.

6. SCR feedforward control device according to claim 5, is characterized in that, described adjusted value acquiring unit, comprises proportion adjustment and integral adjustment pi controller:

Described pi controller is used for:

Generate the ratio of described difference and described average storage ammonia density setting value;

With the integral result of described difference for the integral algorithm CMOS macro cell of parameter through presetting;

Urea-spray adjustment amount is generated according to described ratio and described integral result.