Post-processing system urea crystallization control method, device, and post-processing system

Abstract

The application provides a urea crystallization control method, device and aftertreatment system, and solves the technical problems of difficulty in arranging the whole vehicle, excessive crystallization of the mixer, reduced efficiency of SCR catalytic conversion and increased nitrogen oxides emitted from the tail gas in the prior art. The urea crystallization control method provided by the application obtains the temperature before the first nitrogen oxide treatment device, the exhaust gas mass flow, the front-stage urea injection amount of the front-stage urea mixer, calculates the urea crystallization amount of the front-stage urea mixer according to the temperature before the first nitrogen oxide treatment device, the exhaust gas mass flow and the front-stage urea injection amount of the front-stage urea mixer, and controls the crystallization amount in stages according to the urea crystallization amount of the front-stage urea mixer. The application can control the crystallization amount of the front-stage urea mixer in stages on the basis of the arrangement space of the existing aftertreatment, so as to reduce the difficulty in arranging the whole vehicle and reduce the emission of nitrogen oxides and particulate matters.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile exhaust emission, in particular to a post-processing system urea crystallization control method and device and a post-processing system. BACKGROUND

[0002] With the development of the national seven-stage emission regulations, the emission of nitrogen oxides and particulate matter is further strictly required. The arrangement space of the national six-stage post-processing has been fixed, and the re-arrangement of the post-processing space not only greatly increases the development cost, but also may cause installation difficulties due to the large volume of the newly developed post-processing space. In addition, there is a problem that too much crystallization of the mixer reduces the efficiency of the SCR catalytic conversion, which easily leads to an increase in the emission of nitrogen oxides.

[0003] In the prior art, the front-stage urea mixer A1 is usually arranged on the pipeline at the outlet of the engine turbine, and the urea injection is also after the turbine. Since the mixed gas is a certain distance away from the post-processing box, the mixer is simple and not easy to crystallize, which can reduce the emission of nitrogen oxides, but the arrangement of the mixer is difficult, thereby increasing the arrangement difficulty of the whole vehicle, and the arrangement still needs to be adjusted separately for different vehicle models.

[0004] Therefore, it is necessary to provide a post-processing system urea crystallization control method which can be implemented on the basis of the existing national six-stage post-processing arrangement space, the whole vehicle arrangement is simple, and the emission of nitrogen oxides and particulate matter can be reduced. SUMMARY

[0005] Therefore, the present application provides a post-processing system urea crystallization control method and device, a post-processing system and a vehicle. On the basis of the existing post-processing arrangement space, the crystallization amount is controlled in stages according to the urea crystallization amount of the front-stage urea mixer, so as to reduce the arrangement difficulty of the whole vehicle and reduce the emission of nitrogen oxides and particulate matter.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: a post-processing system urea crystallization control method, the control method is applicable to a post-processing system, the post-processing system comprises: a front-stage urea mixer, which sprays front-stage urea and mixes the sprayed urea with exhaust gas; a first nitrogen oxide treatment device, which adopts a reducing catalyst and an oxidizing catalyst, reduces nitrogen oxides by using the front-stage urea sprayed by the front-stage urea mixer, and oxidizes ammonia; a particulate treatment device, which adopts an oxidizing catalyst to capture particulate matter and nitrogen oxides; a rear-stage urea mixer, which mixes rear-stage urea sprayed after the particulate treatment device with exhaust gas; and a second nitrogen oxide treatment device, which adopts a reducing catalyst and an oxidizing catalyst, reduces nitrogen oxides by using the urea sprayed after the particulate treatment device, and oxidizes ammonia.

[0007] The control method comprises:

[0008] The temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device are obtained, as well as the amount of urea injected into the pre-stage urea mixer.

[0009] Based on the temperature before the first nitrogen oxide treatment device and the mass flow rate of the exhaust gas, the amount of urea injected into the pre-stage urea mixer is calculated to determine the amount of urea crystallization in the pre-stage urea mixer.

[0010] The amount of crystallization is controlled in stages based on the amount of urea crystallization in the upstream urea mixer.

[0011] In one embodiment of this application, obtaining the temperature before the first nitrogen oxide treatment device includes:

[0012] The temperature and exhaust gas mass flow rate before the pre-stage urea mixer are obtained, as well as the pre-stage urea injection quantity of the pre-stage urea mixer.

[0013] The temperature before the first nitrogen oxide treatment device is calculated based on the temperature before the pre-stage urea mixer, the mass flow rate of the exhaust gas, and the pre-stage urea injection rate of the pre-stage urea mixer.

[0014] In one embodiment of this application, the amount of crystallization is controlled in stages according to the amount of urea crystallization in the pre-stage urea mixer, including:

[0015] When the amount of urea crystals in the front-stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the front stage is reduced, and the amount of urea injected into the rear stage is increased.

[0016] In one embodiment of this application, the control method further includes:

[0017] When the amount of crystallization is less than or equal to the second preset threshold, the graded control of the amount of crystallization is terminated, wherein the first preset threshold is greater than the second preset threshold.

[0018] In one embodiment of this application, the method of graded control of the amount of urea crystallization based on the amount of urea crystallization in the pre-stage urea mixer further includes:

[0019] When the amount of urea crystals in the pre-stage urea mixer is greater than or equal to a third preset threshold, the engine thermal management system is activated to raise the temperature before the pre-stage urea mixer, wherein the third preset threshold is greater than the first preset threshold.

[0020] In one embodiment of this application, the control method further includes:

[0021] When the amount of crystallization is less than or equal to the fourth preset threshold, the graded control of the amount of crystallization is terminated, wherein the third preset threshold is greater than the fourth preset threshold.

[0022] In one embodiment of this application, obtaining the pre-stage urea injection volume of the pre-stage urea mixer includes:

[0023] The temperature after the first nitrogen oxide treatment device is obtained;

[0024] The average temperature of the first nitrogen oxide treatment device is calculated based on the temperature before and after the first nitrogen oxide treatment device.

[0025] The nitrogen oxide conversion efficiency is determined based on the mapping relationship between the average temperature and space velocity of the first nitrogen oxide treatment unit.

[0026] The amount of urea injected into the pre-stage urea mixer is calculated based on the exhaust gas mass flow rate, the nitrogen oxide concentration before the pre-stage urea mixer, and the nitrogen oxide conversion efficiency.

[0027] As a second aspect of this application, this application also provides a urea crystallization control device for a post-treatment system, comprising:

[0028] The data acquisition module is used to acquire the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device, and the amount of urea injected into the pre-stage urea mixer.

[0029] The calculation module calculates the amount of urea crystallization in the pre-stage urea mixer based on the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the amount of urea injected into the pre-stage urea mixer.

[0030] The control module is used to control the amount of crystallization in stages based on the amount of urea crystallization in the upstream urea mixer.

[0031] As a third aspect of this application, this application also provides a post-processing system, including:

[0032] The pre-urea mixer injects pre-urea and mixes the injected urea with the exhaust gas;

[0033] The first nitrogen oxide treatment unit uses a reducing catalyst and an oxidizing catalyst, and uses the pre-stage urea injected by the pre-stage urea mixer to reduce nitrogen oxides and oxidize ammonia.

[0034] Particulate matter processors use oxidizing catalysts to capture particulate matter and nitrogen oxides;

[0035] The post-stage urea mixer mixes the post-stage urea injected after the particulate treatment unit with the exhaust gas.

[0036] The second nitrogen oxide treatment unit uses a reducing catalyst and an oxidizing catalyst, and uses urea injected after the particulate treatment unit to reduce nitrogen oxides and oxidize ammonia.

[0037] The controller is used to acquire the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the injection rate of the pre-stage urea in the pre-stage urea mixer; calculate the amount of urea crystallization in the pre-stage urea mixer based on the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the injection rate of the pre-stage urea in the pre-stage urea mixer; and perform graded control on the amount of urea crystallization based on the amount of urea crystallization in the pre-stage urea mixer.

[0038] As a fourth aspect of this application, this application also provides a vehicle, comprising:

[0039] The post-processing system described in the third aspect above;

[0040] This application provides a method for controlling urea crystallization in an aftertreatment system. The aftertreatment system sequentially includes a pre-stage urea mixer, a first nitrogen oxide treatment device, a particulate matter treatment device, a post-stage urea mixer, and a second nitrogen oxide treatment device. Without altering the original layout space of the aftertreatment system, the method changes the position of the pre-stage urea mixer and injects pre-stage urea into it, achieving urea mixing with exhaust gas. This reduces the difficulty of mixer placement, thereby simplifying overall vehicle layout and making it suitable for different vehicle models. Furthermore, by acquiring the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device, and the pre-stage urea injection rate of the pre-stage urea mixer, the urea crystallization amount in the pre-stage urea mixer is calculated, and the crystallization amount is controlled in stages to improve the efficiency of SCR catalytic conversion, thereby reducing nitrogen oxide and particulate matter emissions. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of a post-processing system provided in an embodiment of this application.

[0043] Figure 2 This is a schematic flowchart of a urea crystallization control method in a post-treatment system provided in an embodiment of this application.

[0044] Figure 3 This is a schematic flowchart illustrating a method for obtaining the temperature before a first nitrogen oxide treatment device, provided in an embodiment of this application.

[0045] Figure 4 This is a flowchart illustrating a method for obtaining the amount of urea injected into a pre-stage urea mixer, as provided in an embodiment of this application.

[0046] Figure 5 This is a schematic flowchart of a urea crystallization control method for a post-treatment system provided in another embodiment of this application.

[0047] Figure 6 This is a schematic flowchart of a urea crystallization control method for a post-treatment system provided in another embodiment of this application.

[0048] Figure 7 This is a schematic flowchart of a urea crystallization control method for a post-treatment system provided in another embodiment of this application.

[0049] Figure 8 This is a schematic flowchart of a urea crystallization control method for a post-treatment system provided in another embodiment of this application.

[0050] Figure 9 This is a schematic diagram of the structure of a urea crystallization control device for a post-treatment system provided in an embodiment of this application. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] For ease of description, some of the nouns or terms used in the embodiments of the present invention are explained below:

[0053] DPF (diesel particulate filter) is used to capture particulate matter in exhaust gas. When the mass of captured particulate matter reaches a certain level, passive or active regeneration is required to restore the DPF's ability to capture particulate matter.

[0054] The working principle of DPF active regeneration (high temperature regeneration) is as follows: the temperature of DPF is raised to about 600℃, and the carbon in DPF reacts with oxygen to achieve the purpose of eliminating carbon in DPF.

[0055] DPF internal reaction principle:

[0056]

[0057] The working principle of passive regeneration of DPF is as follows: NO2 reacts with carbon in DPF. NO2 has a strong oxidizing ability on the captured particulate matter (carbon). NO2 generated by the pre-processed DOC is used as an oxidant to remove particulate matter from the particulate trap and generate CO2. NO2 is then reduced to NO, thereby achieving the purpose of removing particulate matter.

[0058] DPF internal reaction principle:

[0059]

[0060] DOC (diesel oxide catalyst) is installed before the DPF to oxidize NO in the exhaust gas to NO2, while also increasing the exhaust gas temperature and assisting the normal operation of the DPF and SCR (selectively catalytic reduction).

[0061] DOC internal reaction principle:

[0062]

[0063] DDPF: An integrated oxidation trap that is coated with both DOC-formulated and DPF-formulated catalysts in separate sections, combining the functions of both DPF and DOC.

[0064] Exemplary System

[0065] As a first aspect of this application, this application provides a post-processing system. Figure 1 The diagram shown is a structural schematic of a post-processing system provided in an embodiment of this application. Figure 1 As shown, the processing system provided in this application includes:

[0066] The pre-stage urea mixer A1 includes a urea nozzle Inj1, which sprays pre-stage urea and mixes the sprayed urea with the exhaust gas to form a uniform mixture.

[0067] The first nitrogen oxide treatment device A2 may include a selective catalytic conversion device (SCR) and an ammonia escape trap (ASC), employing a reducing catalyst and an oxidizing catalyst, and using pre-stage urea injected by a pre-stage urea mixer to reduce nitrogen oxides (NOx) and oxidize excess ammonia (NH3).

[0068] The particulate treatment unit A3 uses an oxidizing catalyst to capture particulate matter and nitrogen oxides. The particulate treatment unit A3 may include an oxidation catalytic converter (DOC) and a particulate matter filter (DPF).

[0069] The post-stage urea mixer A4 has a urea nozzle Inj2 installed after the particulate treatment device A3 and before the post-stage urea mixer A4. The post-stage urea mixer A4 mixes the post-stage urea injected after the particulate treatment device with the exhaust gas to form a uniform mixture.

[0070] The second nitrogen oxide treatment device A5 may include a selective catalytic conversion device (SCR) and an ammonia escape trap (ASC), employing a reducing catalyst and an oxidizing catalyst, and using urea injected after the particulate treatment device to reduce nitrogen oxides (NOx) and oxidize excess ammonia (NH3).

[0071] The controller is used to acquire the temperature, exhaust gas mass flow rate and pre-stage urea injection quantity of the pre-stage urea mixer before the first nitrogen oxide treatment device A2, calculate the urea crystallization amount of the pre-stage urea mixer A1 based on the temperature, exhaust gas mass flow rate and pre-stage urea injection quantity of the pre-stage urea mixer, and perform graded control on the crystallization amount based on the urea crystallization amount of the pre-stage urea mixer A1.

[0072] In one embodiment of this application, the post-treatment system may further include a temperature sensor for detecting the temperature of the exhaust gas at different stages, such as... Figure 1 As shown, the first temperature sensor T1, installed before the pre-urea mixer A1, can detect the first temperature of the exhaust gas before the pre-urea mixer A1; the second temperature sensor T2, installed between the first nitrogen oxide treatment device A2 and the particulate treatment device A3, can detect the second temperature of the exhaust gas after the first nitrogen oxide treatment device A2; and the third temperature sensor T3, installed after the particulate treatment device A3, can detect the third temperature of the exhaust gas after the particulate treatment device A3.

[0073] In one embodiment of this application, the post-treatment system may further include a nitrogen oxide sensor for detecting the concentration of nitrogen oxides (NOx) in the exhaust gas at different stages, such as... Figure 1 As shown, the first nitrogen oxide sensor N1, located before the pre-urea mixer A1, can detect the first nitrogen oxide concentration in the exhaust gas before the pre-urea mixer A1; the second nitrogen oxide sensor N2, located between the first nitrogen oxide treatment device A2 and the particulate treatment device A3, can detect the second nitrogen oxide concentration in the exhaust gas before the particulate treatment device A3; and the third nitrogen oxide sensor N3, located after the second nitrogen oxide treatment device A5, can detect the third nitrogen oxide concentration in the exhaust gas after the second nitrogen oxide treatment device A5.

[0074] The aftertreatment system provided in this application, by placing the pre-stage urea mixer A1 and urea nozzles at the rear, significantly reduces the difficulty of mixer placement compared to existing technologies where the pre-stage urea mixer A1 is located on the engine turbine outlet pipeline and urea injection is also after the turbine, thus simplifying the overall vehicle layout and making it suitable for various vehicle models. Furthermore, by calculating the amount of urea crystals in the pre-stage urea mixer A1, the crystallization amount is controlled in stages, ensuring it remains within a preset range. This improves the efficiency of SCR catalytic conversion, thereby reducing emissions of nitrogen oxides and particulate matter.

[0075] Exemplary methods

[0076] As a second aspect of this application, this application also provides a method for controlling urea crystallization in a post-treatment system, for controlling... Figure 1 The post-processing system shown, Figure 2 The diagram shown is a schematic flow chart of a urea crystallization control method in a post-treatment system according to an embodiment of this application. Figure 2 As shown, a method for controlling urea crystallization in a post-treatment system includes the following steps:

[0077] S10: Obtain the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device, and the amount of urea injected into the pre-stage urea mixer.

[0078] The temperature before the first nitrogen oxide treatment device A2, the mass flow rate of the exhaust gas before the first nitrogen oxide treatment device A2, and the injection volume of the pre-stage urea in the pre-stage urea mixer A1 are obtained respectively.

[0079] S20: Calculate the amount of urea crystallization in the pre-stage urea mixer based on the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device and the pre-stage urea injection rate of the pre-stage urea mixer.

[0080] After determining the temperature before the first nitrogen oxide treatment device A2, the mass flow rate of the exhaust gas before the first nitrogen oxide treatment device A2, and the injection amount of the pre-stage urea in the pre-stage urea mixer A1, the amount of urea crystallization in the pre-stage urea mixer A1 can be calculated based on the temperature before the first nitrogen oxide treatment device A2, the mass flow rate of the exhaust gas before the first nitrogen oxide treatment device A2, and the injection amount of the pre-stage urea in the pre-stage urea mixer A1.

[0081] The specific calculation formula for the urea crystallization amount m of the pre-urea mixer A1 is shown in Formula 1:

[0082] Formula 1

[0083] Where m: amount of urea crystals, g;

[0084] : Urea flow rate, kg / s;

[0085] : Exhaust gas mass flow rate, kg / s;

[0086] Crystallization rate coefficient based on flow rate and temperature;

[0087] Crystallization conversion coefficient based on current crystallization amount and temperature;

[0088] T20: Temperature before the first nitrogen oxide treatment unit A2;

[0089] Interval time.

[0090] S30: The amount of crystallization is controlled in stages according to the amount of urea crystallization in the upstream urea mixer.

[0091] As time accumulates, the amount of urea crystals in the pre-stage urea mixer A1 will increase. When the amount of urea crystals in the pre-stage urea mixer A1 is large, the efficiency of SCR catalytic conversion in the first nitrogen oxide treatment device A2 will decrease, resulting in an increase in nitrogen oxides emitted from the tail gas of the first nitrogen oxide treatment device A2. Ultimately, this will cause the nitrogen oxides emitted from the tail gas of the second nitrogen oxide treatment device A5 in the aftertreatment system to fail to meet the standards.

[0092] This application calculates the amount of urea crystallization in the pre-stage urea mixer A1, sets a threshold for the amount of urea crystallization, and determines whether the amount of urea crystallization in the pre-stage urea mixer A1 exceeds the standard by comparing the amount of urea crystallization with the threshold. This allows for graded control of the amount of urea crystallization, ensuring that the amount of urea crystallization in the pre-stage urea mixer A1 is controlled within a preset range.

[0093] In one embodiment of this application, the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device A2, and the pre-stage urea injection rate of the pre-stage urea mixer A1 are obtained. Based on the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device A2, and based on the pre-stage urea injection rate of the pre-stage urea mixer A1, the urea crystallization amount of the pre-stage urea mixer A1 is calculated. Based on the urea crystallization amount of the pre-stage urea mixer A1, the crystallization amount is controlled in stages, so that the urea crystallization amount of the pre-stage urea mixer A1 is controlled within a preset range, thereby improving the efficiency of SCR catalytic conversion and reducing the emissions of nitrogen oxides and particulate matter.

[0094] In one embodiment of this application, as Figure 3 As shown, the specific steps for obtaining the temperature before the first nitrogen oxide treatment device in S10 may include:

[0095] S211: Obtain the temperature and exhaust gas mass flow rate before the pre-stage urea mixer, and the pre-stage urea injection volume of the pre-stage urea mixer.

[0096] The temperature before the pre-stage urea mixer A1, the exhaust gas mass flow rate before the pre-stage urea mixer A1, and the pre-stage urea injection quantity of the pre-stage urea mixer A1 are obtained respectively. Specifically, the temperature before the pre-stage urea mixer A1 can be obtained by acquiring the temperature of the first temperature sensor T1 located before the pre-stage urea mixer A1. The exhaust gas mass flow rate is related to the air intake volume and fuel quantity. Specifically, the theoretical maximum air mass refers to the air mass that the cylinder working volume can hold under the intake manifold temperature and pressure conditions. Based on the intake manifold temperature and pressure sensor values ​​and engine speed, the theoretical air mass can be calculated. At the same time, the charge coefficient is calibrated, and the actual intake volume can be calculated. The charge coefficient is the ratio of the actual fresh air mass entering the cylinder to the theoretical maximum air mass. The fuel quantity is determined according to the injection quantity required by the ECU. The specific calculation formula for the exhaust gas mass flow rate is shown in Formula 2.

[0097] Air = P / (RT)*V*n / 2*eff (Formula 2)

[0098] Where P / (RT): ideal gas equation, used to calculate air density under intake manifold conditions;

[0099] V*n / 2: The product of engine displacement and engine speed, used to calculate the volumetric flow rate of air at that engine speed;

[0100] eff: Fill factor;

[0101] The specific method for obtaining the pre-urea injection volume of the pre-urea mixer will be explained in detail later.

[0102] S212: Calculate the temperature before the first nitrogen oxide treatment device based on the temperature before the pre-stage urea mixer, the exhaust gas mass flow rate, and the pre-stage urea injection rate of the pre-stage urea mixer.

[0103] After determining the temperature before the pre-urea mixer A1, the exhaust gas mass flow rate before the pre-urea mixer A1, and the pre-urea injection quantity of the pre-urea mixer A1, the temperature before the first nitrogen oxide treatment device A2 can be calculated based on the temperature before the pre-urea mixer A1, the exhaust gas mass flow rate before the pre-urea mixer A1, and the pre-urea injection quantity of the pre-urea mixer A1.

[0104] The specific calculation formula for the temperature T20 before the first nitrogen oxide treatment unit A2 is shown in Formula 3:

[0105] Formula 3

[0106] in, Specific heat capacity of urea, J / kg / k;

[0107] : Urea flow rate, kg / s;

[0108] T0: Urea temperature, K;

[0109] Specific heat capacity of exhaust gas, J / kg / K;

[0110] : Exhaust gas mass flow rate, kg / s;

[0111] Latent heat of vaporization of water, J / mol;

[0112] Molar mass of water, kg / mol;

[0113] Molar mass of urea, kg / mol;

[0114] Gibbs free energy of urea decomposition, J / mol.

[0115] In one embodiment of this application, as Figure 4 As shown, the specific steps for obtaining the pre-stage urea injection volume of the pre-stage urea mixer in S10 may include:

[0116] S221: Obtain the temperature after the first nitrogen oxide treatment device.

[0117] Specifically, the temperature after the first nitrogen oxide treatment device A2 can be obtained by acquiring the second temperature sensor T2 located after the first nitrogen oxide treatment device A2.

[0118] S222: Calculate the average temperature of the first nitrogen oxide treatment device based on the temperature before the first nitrogen oxide treatment device and the temperature after the first nitrogen oxide treatment device.

[0119] After determining the temperature before and after the first nitrogen oxide treatment device, the average temperature T of the first nitrogen oxide treatment device A2 can be calculated based on the temperature T20 before and the temperature T2 after the first nitrogen oxide treatment device A2, where T = (T20 + T2) / 2.

[0120] S223: Determine the nitrogen oxide conversion efficiency of the first nitrogen oxide treatment device based on the mapping relationship between the average temperature and space velocity of the first nitrogen oxide treatment device.

[0121] After determining the average temperature T and space velocity of the first nitrogen oxide treatment device A2, the nitrogen oxide conversion efficiency of the first nitrogen oxide treatment device A2 can be obtained according to the nitrogen oxide conversion efficiency MAP table. The nitrogen oxide conversion efficiency MAP table is obtained through experiments and simulations on the post-treatment system and includes the relationship between temperature, space velocity and nitrogen oxide conversion efficiency. Using the average temperature T and space velocity of the first nitrogen oxide treatment device A2 as input parameters, the corresponding nitrogen oxide conversion efficiency in the first nitrogen oxide treatment device A2 can be found through the MAP table. In addition, the space velocity can be determined by the exhaust gas mass flow rate, exhaust gas density and the volume of the first nitrogen oxide treatment device A2. Specifically, space velocity = exhaust gas mass flow rate / (exhaust gas density * volume of the first nitrogen oxide treatment device A2).

[0122] S224: Calculate the amount of urea injected into the pre-stage urea mixer based on the exhaust gas mass flow rate, the nitrogen oxide concentration before the pre-stage urea mixer, and the nitrogen oxide conversion efficiency of the first nitrogen oxide treatment device.

[0123] While determining the nitrogen oxide conversion efficiency of the first nitrogen oxide treatment device A2, the mass flow rate of the exhaust gas before the pre-urea mixer A1 and the nitrogen oxide concentration before the pre-urea mixer A1 are obtained. The specific nitrogen oxide concentration before the pre-urea mixer A1 can be obtained through the first nitrogen oxide sensor N1 installed before the pre-urea mixer A1. Based on the mass flow rate of the exhaust gas before the pre-urea mixer A1 and the nitrogen oxide concentration before the pre-urea mixer A1, the mass flow rate of nitrogen oxides (NOx) entering the nitrogen oxide treatment device A2 is calculated, where the molar mass of NOx is 46 g / mol. The specific mass flow rate of nitrogen oxides (NOx) = mass flow rate of exhaust gas before the pre-urea mixer A1 * NOx concentration before the pre-urea mixer A1 * 46 / 29 * (1e-6).

[0124] The amount of nitrogen oxides converted at A2 before the nitrogen oxide treatment unit can be calculated by multiplying the nitrogen oxide conversion efficiency of A2 before the nitrogen oxide treatment unit. The mass flow rate of ammonia is then calculated based on this conversion rate. The specific formula is: Mass flow rate of ammonia = Amount of nitrogen oxides converted at A2 before the nitrogen oxide treatment unit * 17 / 46.

[0125] Finally, the amount of urea injected into the pre-stage urea mixer A1 is calculated based on the mass flow rate of ammonia. The molar mass of urea is 60 g / mol, 1 mol of urea contains 2 mol of ammonia, and the molar mass of ammonia is 17 g / mol. The amount of urea injected into the pre-stage urea is calculated as: mass flow rate of ammonia * 60 / (2 * 17 * concentration of urea solution).

[0126] In one embodiment of this application, as Figure 5 As shown, in S30, the amount of crystallization is controlled in stages according to the amount of urea crystallization in the upstream urea mixer. Specific steps may include:

[0127] S31: When the amount of urea crystals in the current stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the previous stage is reduced, and the amount of urea injected into the subsequent stage is increased.

[0128] A first preset threshold is set in advance, for example, the first preset threshold is 10g. After calculating the amount of urea crystallization in the pre-stage urea mixer A1, the amount of urea crystallization in the pre-stage urea mixer A1 is compared with the first preset threshold. When the amount of urea crystallization in the pre-stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the pre-stage mixer is reduced, and the amount of urea injected into the post-stage mixer is increased.

[0129] Specifically, the amount of urea injected into the pre-stage can be controlled according to the steps S221 to S224 above.

[0130] In this embodiment, by setting a first preset threshold for the amount of urea crystallization in the pre-stage urea mixer A1, the amount of urea crystallization can be controlled. This allows for precise control of the urea injection amount, avoiding crystallization caused by excessive injection. This not only improves the utilization efficiency of urea but also ensures the efficient operation of the exhaust gas treatment system. Furthermore, reducing urea crystallization in the pre-stage urea mixer A1 ensures the cleanliness of the catalyst surface of the first nitrogen oxide treatment device A2, thereby improving the nitrogen oxide conversion efficiency of the first nitrogen oxide treatment device A2 and ensuring that the nitrogen oxides emitted from the exhaust gas of the first nitrogen oxide treatment device A2 meet the standards.

[0131] In one embodiment of this application, obtaining the injection volume of the downstream urea from the downstream urea mixer may include the following steps:

[0132] S231: Obtain the temperature after the particle processing device.

[0133] Specifically, the temperature after particle processing device A3 can be obtained by using a third temperature sensor T3 installed after particle processing device A3.

[0134] S232: Determine the nitrogen oxide conversion efficiency of the second nitrogen oxide treatment unit based on the mapping relationship between temperature and space velocity after the particle treatment unit.

[0135] Similarly, after determining the temperature T3 and space velocity after the particulate treatment unit A3, the nitrogen oxide conversion efficiency of the second nitrogen oxide treatment unit A5 can be obtained according to the nitrogen oxide conversion efficiency MAP table. In addition, the space velocity can be determined by the exhaust gas mass flow rate, exhaust gas density, and the volume of the second nitrogen oxide treatment unit A5. Specifically, space velocity = exhaust gas mass flow rate / (exhaust gas density * volume of the second nitrogen oxide treatment unit A5).

[0136] S233: Calculate the proportion of nitrogen dioxide in nitrogen oxides, and correct the nitrogen oxide conversion efficiency of the second nitrogen oxide treatment device based on the proportion of nitrogen dioxide in nitrogen oxides.

[0137] The proportion of nitrogen dioxide in nitrogen oxides is equal to the ratio of nitrogen dioxide to nitrogen oxides.

[0138] S234: Calculate the amount of urea injected into the downstream urea mixer based on the exhaust gas mass flow rate, the nitrogen oxide concentration before the particulate treatment device, and the nitrogen oxide conversion efficiency of the second nitrogen oxide treatment device.

[0139] While determining the nitrogen oxide conversion efficiency of the second nitrogen oxide treatment device A5, the mass flow rate of the exhaust gas before the second nitrogen oxide treatment device A5 and the nitrogen oxide concentration before the particulate treatment device A3 are obtained. Specifically, the nitrogen oxide concentration of the exhaust gas before the particulate treatment device A3 can be detected by the second nitrogen oxide sensor N2, which is installed between the first nitrogen oxide treatment device A2 and the particulate treatment device A3. Based on the mass flow rate of the exhaust gas before the second nitrogen oxide treatment device A5, the nitrogen oxide concentration before the particulate treatment device A3, and the nitrogen oxide conversion efficiency of the second nitrogen oxide treatment device A5, the downstream urea injection rate of the downstream urea mixer A4 can be calculated. The specific calculation process is the same as the calculation process of the upstream urea injection rate of the upstream urea mixer, and will not be described in detail here.

[0140] It is understandable that the amount of urea injected in the later stage can be controlled according to the above steps S231 to S234.

[0141] In one embodiment of this application, as Figure 6 As shown, when the amount of urea crystallization in the current stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the preceding stage is reduced, and the amount of urea injected into the following stage is increased. That is, after S31, the following steps may also be included:

[0142] S40: When the amount of crystallization is less than or equal to the second preset threshold, exit the graded control of the amount of crystallization.

[0143] After implementing the steps of reducing the amount of urea injected into the pre-stage urea and increasing the amount of urea injected into the post-stage urea, the amount of urea crystallization in the pre-stage urea mixer A1 may show an increasing trend or a decreasing trend. If the amount of urea crystallization in the pre-stage urea mixer shows a decreasing trend, the amount of urea crystallization in the pre-stage urea mixer A1 is monitored and compared with the second preset threshold. When the amount of crystallization is less than or equal to the second preset threshold, the amount of urea crystallization in the pre-stage urea mixer A1 has met the preset requirements, resulting in a high efficiency of SCR catalytic conversion in the first nitrogen oxide treatment device A2. The nitrogen oxides emitted from the tail gas of the first nitrogen oxide treatment device A2 meet the standards, and ultimately the nitrogen oxides emitted from the tail gas of the second nitrogen oxide treatment device A5 in the aftertreatment system also meet the standards. Therefore, it is temporarily unnecessary to control the amount of urea crystallization in the pre-stage urea mixer A1. The first preset threshold is greater than the second preset threshold, and the second preset threshold is also preset, for example, the second preset threshold is 3g.

[0144] In this embodiment, by setting a second preset threshold for the amount of crystallization, the timing for exiting control of the amount of urea crystallization in the pre-stage urea mixer A1 is given, that is, the amount of urea injected into the pre-stage and the amount of urea injected into the post-stage are no longer controlled, which can avoid unnecessary intervention of the post-treatment system on the amount of urea crystallization during normal operation.

[0145] In one embodiment of this application, as Figure 7 As shown, when the amount of urea crystallization in the current stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the preceding stage is reduced, and the amount of urea injected into the following stage is increased. That is, after S31, the following steps may also be included:

[0146] S32: When the amount of urea crystals in the pre-stage urea mixer is greater than or equal to the third preset threshold, the engine thermal management system is activated to increase the temperature in front of the pre-stage urea mixer.

[0147] After controlling the reduction of the pre-stage urea injection quantity and the increase of the post-stage urea injection quantity, if the urea crystallization amount in the pre-stage urea mixer shows an increasing trend, the urea crystallization amount in the pre-stage urea mixer A1 is continuously monitored and compared with a third preset threshold. If the urea crystallization amount in the pre-stage urea mixer A1 is greater than or equal to the third preset threshold, then the urea crystallization amount is excessive. Continuing to control the reduction of the pre-stage urea injection quantity and the increase of the post-stage urea injection quantity will not effectively reduce the urea crystallization amount. In this case, the engine thermal management system is activated, for example, by retarding the engine's advance angle or reducing the intake air volume, to worsen combustion and increase the exhaust gas temperature after the turbine, i.e., to increase the exhaust gas temperature before the pre-stage urea mixer A1. The third preset threshold is greater than the first preset threshold, and the third preset threshold is also preset, for example, 20g.

[0148] In this embodiment, by setting two preset thresholds for the amount of crystallization, a third preset threshold, and a first preset threshold (the third preset threshold is greater than the first preset threshold), the amount of urea crystallization in the aftertreatment system is reduced in stages. When the amount of urea crystallization in the pre-stage urea mixer A1 is greater than or equal to the first preset threshold, only the injection amounts of the pre-stage and post-stage urea are controlled to reduce the amount of urea crystallization. When the amount of urea crystallization in the pre-stage urea mixer A1 is greater than or equal to the third preset threshold, the engine thermal management system is activated to increase the temperature before the pre-stage urea mixer, thereby further reducing the amount of urea crystallization. That is, for different types of urea... Different control methods are used for the amount of crystallization. This dual-threshold strategy can more precisely control the amount of urea crystallization, improve the reliability of the post-treatment system and the efficiency of removing urea crystals, and ensure that the amount of urea crystallization in the pre-stage urea mixer A1 is always within the preset range. This improves the efficiency of SCR catalytic conversion in the first nitrogen oxide treatment unit A2, thereby reducing the nitrogen oxide emissions from the first nitrogen oxide treatment unit A2. This reduces the risk of crystallization in the subsequent urea mixer A4, and ultimately improves the efficiency of SCR catalytic conversion in the second nitrogen oxide treatment unit A5, ensuring that the final emissions of nitrogen oxides and particulate matter meet the standards.

[0149] In one embodiment of this application, as Figure 8 As shown, when the amount of urea crystals in the current stage urea mixer is greater than or equal to the third preset threshold, the engine thermal management system is activated to raise the temperature before the current stage urea mixer. That is, after S32, the following steps may also be included:

[0150] S50: When the amount of crystallization is less than or equal to the fourth preset threshold, exit the graded control of the amount of crystallization.

[0151] After implementing the engine thermal management system to increase the temperature before the pre-stage urea mixer, if the amount of urea crystallization in the pre-stage urea mixer shows a decreasing trend, the amount of urea crystallization in the pre-stage urea mixer A1 continues to be monitored and compared with the fourth preset threshold. When the amount of crystallization is less than or equal to the fourth preset threshold, the amount of urea crystallization in the pre-stage urea mixer A1 has met the preset requirements, which can make the SCR catalytic conversion efficiency in the first nitrogen oxide treatment device A2 higher, and the nitrogen oxides emitted from the exhaust gas of the first nitrogen oxide treatment device A2 meet the standards. Ultimately, the nitrogen oxides emitted from the exhaust gas of the second nitrogen oxide treatment device A5 in the aftertreatment system also meet the standards. Therefore, it is temporarily unnecessary to control the amount of urea crystallization in the pre-stage urea mixer A1, that is, to exit the graded control of the amount of crystallization. The third preset threshold is greater than the fourth preset threshold, and the fourth preset threshold is also preset, for example, the fourth preset threshold is 3g. Although both the fourth preset threshold and the second preset threshold are crystallization thresholds for exiting graded control of crystallization amount, they do not have a clear relationship in magnitude. The fourth preset threshold and the second preset threshold can be equal or unequal.

[0152] By setting a fourth preset threshold for the amount of crystallization, the timing for exiting control of the amount of urea crystallization in the pre-stage urea mixer A1 is given. That is, the control of the pre-stage urea injection quantity, the post-stage urea injection quantity, and the engine thermal management is no longer required. This avoids unnecessary intervention of the aftertreatment system on the amount of urea crystallization during normal operation, reduces unnecessary heating operations, reduces energy consumption, and improves the overall energy efficiency of the aftertreatment system.

[0153] Exemplary device

[0154] As a third aspect of this application, this application also provides a urea crystallization control device for a post-treatment system. Figure 9 The diagram shown is a working block diagram of a urea crystallization control device for a post-treatment system according to an embodiment of this application. Figure 9 As shown, the fault self-recovery controller 900 includes:

[0155] The data acquisition module 901 is used to acquire the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device, and the amount of urea injected into the pre-stage urea mixer.

[0156] Specifically, the data acquisition module 901 is used to execute the steps in S10 of the above-described urea crystallization control method for the post-treatment system, namely, acquiring the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device, and the amount of urea injected into the pre-stage urea mixer.

[0157] The calculation module 902 is used to calculate the amount of urea crystallization in the pre-stage urea mixer based on the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device and the amount of pre-stage urea injected into the pre-stage urea mixer.

[0158] Specifically, the calculation module 902 is used to execute the step in S20 of the urea crystallization control method of the post-treatment system described above, which calculates the amount of urea crystallization in the pre-stage urea mixer based on the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the amount of pre-stage urea injected into the pre-stage urea mixer.

[0159] The control module 903 is used to control the amount of crystallization in stages based on the amount of urea crystallization in the upstream urea mixer.

[0160] Specifically, the control module 903 is used to execute the step of step S30 in the post-treatment system urea crystallization control method described above, which involves classifying and controlling the amount of crystallization based on the amount of urea crystallization in the pre-stage urea mixer.

[0161] The urea crystallization control device for the aftertreatment system provided in this application acquires the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device A2, and the pre-stage urea injection rate of the pre-stage urea mixer A1. Based on the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device A2, and based on the pre-stage urea injection rate of the pre-stage urea mixer A1, the urea crystallization amount of the pre-stage urea mixer A1 is calculated. Based on the urea crystallization amount of the pre-stage urea mixer A1, the crystallization amount is controlled in stages, so that the urea crystallization amount of the pre-stage urea mixer A1 is controlled within a preset range, thereby improving the efficiency of SCR catalytic conversion and reducing the emissions of nitrogen oxides and particulate matter.

[0162] Furthermore, the urea crystallization control device for the aftertreatment system provided in this embodiment belongs to the same application concept as the urea crystallization control method for the aftertreatment system provided in the above embodiments of this application. It can execute the urea crystallization control method for the aftertreatment system provided in any of the above embodiments of this application, and has the corresponding functional units and beneficial effects for executing the urea crystallization control method for the aftertreatment system. Technical details not described in detail in this embodiment can be found in the specific processing content of the urea crystallization control method for the aftertreatment system provided in the above embodiments of this application, and will not be repeated here.

[0163] Exemplary vehicle

[0164] As a third aspect of this application, this application also provides a vehicle including the after-treatment system described in the first aspect above.

[0165] The methods in this application can be implemented, in whole or in part, by software, hardware, firmware, or any combination thereof. When implemented in software, they can be implemented, in whole or in part, as a computer program product. This computer program product includes one or more computer programs or instructions, which, when loaded and executed on a computer, perform all or part of the processes or functions of this application. The computer can be a general-purpose computer, a special-purpose computer, a computer network, network equipment, user equipment, core network equipment, OAM, or other programmable device.

[0166] Computer program products can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of this application. The programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0167] Computer programs or instructions can be stored in or transferred from one computer-readable storage medium to another. For example, a computer program or instructions can be transferred from one website, computer, server, or data center to another via wired or wireless means. A computer-readable storage medium can be any usable medium that a computer can access, or a data storage device such as a server or data center that integrates one or more usable media. Usable media can be magnetic media, such as floppy disks, hard disks, and magnetic tapes; optical media, such as digital video discs; or semiconductor media, such as solid-state drives. The computer-readable storage medium can be volatile or non-volatile, or may include both types.

[0168] Furthermore, embodiments of this application may also be storage media storing a computer program, which is executed by a processor of the steps in a urea crystallization control method for a post-processing system described in any of the above embodiments of this specification:

[0169] For the foregoing method embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0170] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For apparatus embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0171] The steps in the methods of the various embodiments of this application can be adjusted, combined, or deleted according to actual needs, and the technical features described in each embodiment can be replaced or combined. The apparatuses in the various embodiments of this application can be combined, divided, or deleted according to actual needs.

[0172] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0173] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software unit executed by a processor, or a combination of both. The software unit can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0174] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0175] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling urea crystallization in a post-treatment system, characterized in that, The control method is applicable to an aftertreatment system, which includes: a pre-treatment urea mixer that injects pre-treatment urea and mixes the injected urea with the exhaust gas; a first nitrogen oxide treatment device that uses a reducing catalyst and an oxidizing catalyst to reduce nitrogen oxides and oxidize ammonia using the pre-treatment urea injected by the pre-treatment urea mixer; a particulate treatment device that uses an oxidizing catalyst to capture particulates and nitrogen oxides; a post-treatment urea mixer that mixes the post-treatment urea injected after the particulate treatment device with the exhaust gas; and a second nitrogen oxide treatment device that uses a reducing catalyst and an oxidizing catalyst to reduce nitrogen oxides and oxidize ammonia using the urea injected after the particulate treatment device. The control method includes: The temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device are obtained, as well as the amount of urea injected into the pre-stage urea mixer. Based on the temperature before the first nitrogen oxide treatment device and the mass flow rate of the exhaust gas, the amount of urea injected into the pre-stage urea mixer is calculated to determine the amount of urea crystallization in the pre-stage urea mixer. The amount of crystallization is controlled in stages based on the amount of urea crystallization in the pre-stage urea mixer; Based on the amount of urea crystallization in the upstream urea mixer, the amount of crystallization is controlled in stages, including: When the amount of urea crystals in the front-stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the front-stage mixer is reduced, and the amount of urea injected into the rear-stage mixer is increased. When the amount of crystallization is less than or equal to the second preset threshold, the graded control of the amount of crystallization is terminated, wherein the first preset threshold is greater than the second preset threshold.

2. A method for controlling urea crystallization in a post-treatment system, characterized in that, The control method is applicable to an aftertreatment system, which includes: a pre-treatment urea mixer that injects pre-treatment urea and mixes the injected urea with the exhaust gas; a first nitrogen oxide treatment device that uses a reducing catalyst and an oxidizing catalyst to reduce nitrogen oxides and oxidize ammonia using the pre-treatment urea injected by the pre-treatment urea mixer; a particulate treatment device that uses an oxidizing catalyst to capture particulates and nitrogen oxides; a post-treatment urea mixer that mixes the post-treatment urea injected after the particulate treatment device with the exhaust gas; and a second nitrogen oxide treatment device that uses a reducing catalyst and an oxidizing catalyst to reduce nitrogen oxides and oxidize ammonia using the urea injected after the particulate treatment device. The control method includes: The temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device are obtained, as well as the amount of urea injected into the pre-stage urea mixer. Based on the temperature before the first nitrogen oxide treatment device and the mass flow rate of the exhaust gas, the amount of urea injected into the pre-stage urea mixer is calculated to determine the amount of urea crystallization in the pre-stage urea mixer. The amount of crystallization is controlled in stages based on the amount of urea crystallization in the pre-stage urea mixer; Based on the amount of urea crystallization in the upstream urea mixer, the amount of crystallization is controlled in stages, including: When the amount of urea crystals in the front-stage urea mixer is greater than or equal to the first preset threshold, the amount of urea injected into the front-stage mixer is reduced, and the amount of urea injected into the rear-stage mixer is increased. When the amount of urea crystals in the pre-stage urea mixer is greater than or equal to a third preset threshold, the engine thermal management system is activated to increase the temperature before the pre-stage urea mixer, wherein the third preset threshold is greater than the first preset threshold. When the amount of crystallization is less than or equal to the fourth preset threshold, the graded control of the amount of crystallization is terminated, wherein the third preset threshold is greater than the fourth preset threshold.

3. The method for controlling urea crystallization in a post-treatment system according to claim 1 or 2, characterized in that, The temperatures obtained before the first nitrogen oxide treatment device include: The temperature and exhaust gas mass flow rate before the pre-stage urea mixer are obtained, as well as the pre-stage urea injection quantity of the pre-stage urea mixer. The temperature before the first nitrogen oxide treatment device is calculated based on the temperature before the pre-stage urea mixer, the mass flow rate of the exhaust gas, and the pre-stage urea injection rate of the pre-stage urea mixer.

4. The method for controlling urea crystallization in a post-treatment system according to claim 1 or 2, characterized in that, The process of obtaining the pre-stage urea injection volume of the pre-stage urea mixer includes: The temperature after the first nitrogen oxide treatment device is obtained; The average temperature of the first nitrogen oxide treatment device is calculated based on the temperature before and after the first nitrogen oxide treatment device. The nitrogen oxide conversion efficiency is determined based on the mapping relationship between the average temperature and space velocity of the first nitrogen oxide treatment unit. The amount of urea injected into the pre-stage urea mixer is calculated based on the exhaust gas mass flow rate, the nitrogen oxide concentration before the pre-stage urea mixer, and the nitrogen oxide conversion efficiency.

5. A control device for the urea crystallization control method of the post-treatment system according to any one of the preceding claims, characterized in that, include: The data acquisition module is used to acquire the temperature and exhaust gas mass flow rate before the first nitrogen oxide treatment device, and the amount of urea injected into the pre-stage urea mixer. The calculation module is used to calculate the amount of urea crystallization in the pre-stage urea mixer based on the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the amount of pre-stage urea injected into the pre-stage urea mixer. The control module is used to control the amount of crystallization in stages based on the amount of urea crystallization in the upstream urea mixer.

6. A post-treatment system employing the urea crystallization control method according to any one of claims 1-4, characterized in that, include: The pre-urea mixer injects pre-urea and mixes the injected urea with the exhaust gas; The first nitrogen oxide treatment unit uses a reducing catalyst and an oxidizing catalyst, and uses the pre-stage urea injected by the pre-stage urea mixer to reduce nitrogen oxides and oxidize ammonia. Particulate matter processors use oxidizing catalysts to capture particulate matter and nitrogen oxides; The post-stage urea mixer mixes the post-stage urea injected after the particulate treatment unit with the exhaust gas. The second nitrogen oxide treatment unit uses a reducing catalyst and an oxidizing catalyst, and uses urea injected after the particulate treatment unit to reduce nitrogen oxides and oxidize ammonia. The controller is used to acquire the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the injection rate of the pre-stage urea in the pre-stage urea mixer; calculate the amount of urea crystallization in the pre-stage urea mixer based on the temperature before the first nitrogen oxide treatment device, the mass flow rate of the exhaust gas, and the injection rate of the pre-stage urea in the pre-stage urea mixer; and perform graded control on the amount of urea crystallization based on the amount of urea crystallization in the pre-stage urea mixer.

7. A vehicle, characterized in that, include: The post-processing system as described in claim 6.

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