Response lag compensation method for urea liquid injection system and urea liquid injection system

Abstract

The application provides a response lag compensation method of a urea liquid injection system, which solves the problem of response lag between the urea liquid rate supplied by a metering pump and the urea liquid rate sprayed by a gas-assisted nozzle in the gas-assisted urea injection system, and comprises the following steps: a first-order dynamic system model about the residual urea liquid amount in a urea pipe is constructed to associate the urea liquid rate sprayed by the gas-assisted atomizing nozzle with the urea liquid rate pumped by the metering pump; an imbalance difference between the urea liquid rate pumped by the metering pump and the urea liquid rate sprayed by the gas-assisted atomizing nozzle is obtained, the urea liquid rate sprayed by the gas-assisted atomizing nozzle at t2 is calculated as X2, the required urea liquid injection rate at the next moment t2 is given as Xneed according to the actual working condition of the engine, the urea liquid rate pumped by the metering pump at the next moment t2 is calculated as Y1, the urea liquid rate pumped by the metering pump at the next moment t2 is corrected as Y2 which is calculated to compensate, and in addition, the application also provides a gas-assisted urea liquid injection system applying the method.

Description

Technical Field

[0001] This invention relates to the field of diesel engine exhaust aftertreatment, specifically to a response lag compensation method for a urea injection system and an air-assisted urea injection system using this method. Background Technology

[0002] The operation of the SCR system is as follows: when nitrogen oxides are detected in the exhaust pipe, the gas-assisted urea injection system injects urea. Urea and nitrogen oxides undergo an oxidation-reduction reaction in the SCR catalyst to generate pollution-free nitrogen and water vapor, which are then discharged.

[0003] In an air-assisted urea injection system, the urea solution supplied by the metering pump enters the mixing chamber and mixes with compressed air to form a two-phase flow that flows in the urea pipe before reaching the air-assisted nozzle and being sprayed out. Therefore, if the urea pipe between the mixing chamber and the nozzle is relatively long, the flow rate of urea solution supplied by the metering pump will differ from the flow rate of urea solution sprayed from the air-assisted nozzle. This flow rate difference manifests per unit time as a difference between the rate Y of urea solution supplied by the metering pump and the rate X of urea solution sprayed from the air-assisted nozzle. Thus, when the rate of urea solution demanded by the air-assisted nozzle changes, if the rate Y of urea solution supplied by the metering pump is adjusted synchronously according to the changing demand rate, the rate X of urea solution sprayed from the air-assisted nozzle will not be adjusted immediately, inevitably resulting in a response lag. This leads to an error between the urea solution demand and the actual urea solution adjustment. Although this error is only temporary and will approach zero after a period of stabilization, its existence may still affect the redox reaction of the SCR catalytic converter. Excessive urea concentration will affect the reduction of vehicle exhaust, causing ammonia loss and forming secondary pollutants. Insufficient urea participating in the catalytic reduction reaction will easily lead to excessive nitrogen oxide emissions. Summary of the Invention

[0004] The purpose of this invention is to provide a response lag compensation method for a urea solution injection system, which solves the problem of response lag between the rate of urea solution supplied by the metering pump and the rate of urea solution ejected from the air-assisted nozzle in the air-assisted urea injection system. In addition, this invention also provides an air-assisted urea solution injection system using this method.

[0005] The technical solution is as follows: A method for compensating for response lag in a urea solution injection system, comprising a urea metering pump and an air source, wherein the urea metering pump and the air source are respectively connected to a mixing chamber, and the mixing chamber is connected to an air-assisted atomizing nozzle via a urea pipe, characterized in that the method includes the following steps:

[0006] Step 1: Set the amount of residual urea solution in the urea tube to R, and construct a first-order dynamic system model for the amount of residual urea solution in the urea tube to correlate the rate at which the air-assisted atomizing nozzle sprays urea solution with the rate at which the metering pump pumps urea solution.

[0007] Step 2: Set the current residual urea solution volume in the urea tube to R = R1. At the current time t1, the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as: X1 = R1 / Tc, where Tc is the time constant in the first-order dynamic system model. The current rate at which the metering pump ejects urea solution is Y1. Then, the imbalance difference between the rate at which the metering pump ejects urea solution and the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as:

[0008] DX1 = Y1 - X1;

[0009] Step 3: Based on the first-order dynamic system model, calculate the velocity X2 of urea solution ejected from the air-assisted atomizing nozzle at time t2, expressed as:

[0010] R2=R1+Tc*DX1*(1-exp(-(t2-t1) / Tc))

[0011] X2=R2 / Tc=X1+DX1*(1-exp(-(t2-t1) / Tc))

[0012] Where R2 is the amount of residual urea solution in the urea tube at the next moment, and exp is an exponential function with the natural constant e as the base.

[0013] Step 4: Based on the actual operating conditions of the engine, the required urea injection rate at the next time t2 is given as Xneed. The urea pumping rate at the next time t2 is expressed as Y2 = Xneed + (Xneed - X2) * Ac, where Ac is the difference correction coefficient in the first-order dynamic system model. The urea pumping rate at the next time t2 is corrected to the calculated Y2 for compensation.

[0014] Furthermore, the first-order dynamic system model for the amount of residual urea solution in the urea tube constructed in step 1 is expressed as follows:

[0015] (YX(t))dt=dR(t)

[0016] Where Y is the rate at which the metering pump supplies urea solution, X(t) represents the rate at which the urea solution is ejected from the air-assisted nozzle as a function of time t, d represents the integral, and R(t) represents the amount of residual urea solution R in the urea tube as a function of time t.

[0017] Substituting X(t) = R(t) / Tc into the equation, where Tc is the time constant, we can solve for the following:

[0018] R(t)=R0+Tc*(Y-X0)*(1-exp(-t / Tc))

[0019] X(t)=X0+(Y-X0)*(1-exp(-t / Tc))

[0020] R0 represents the initial amount of residual urea solution in the urea tube, and X0 represents the initial rate at which urea solution is ejected from the air-assisted atomizing nozzle.

[0021] Furthermore, if the residual urea solution R in the urea tube is negative, R = 0; if X2 is negative, X2 = 0; if Y2 is negative, Y2 = 0.

[0022] Furthermore, if ABS((Xneed-X2) / Xneed) is less than the preset error tolerance value Err_limit, then Y2 = Xneed is taken, where Err_limit is the post-processing product standard, representing the error tolerance value.

[0023] Furthermore, if the calculated Y2 is greater than the maximum injection rate Dose_max of the urea metering pump, then Y2 = Dose_max.

[0024] Furthermore, if (t2-t1) is much smaller than Tc, in step 3, the amount of residual urea liquid in the urea tube at the next moment is R2 = R1 + (t2-t1) * DX1, and the rate at which the air-assisted atomizing nozzle sprays urea liquid at the next moment t2 is X2 = R2 / Tc = X1 + (t2-t1) * DX1 / Tc.

[0025] A gas-assisted urea liquid injection system includes a urea metering pump and an air source. The urea metering pump and the air source are respectively connected to a mixing chamber. The mixing chamber is connected to a gas-assisted atomizing nozzle through a urea pipe. The urea liquid pumped by the urea metering pump and the compressed air from the air source enter the mixing chamber sequentially and mix. The resulting air-urea gas-liquid two-phase flow passes through the urea pipe and flows to the gas-assisted atomizing nozzle. The urea metering pump is connected to a controller. The controller executes the response hysteresis compensation method of the gas-assisted urea liquid injection system described above to control the gas-assisted atomizing nozzle to inject urea liquid.

[0026] The response lag compensation method for urea solution injection system provided by this invention constructs a first-order dynamic system model of the amount of residual urea solution in the urea pipe, and correlates the rate of urea solution ejected from the air-assisted nozzle with the rate of urea solution supplied by the metering pump. When the urea injection demand rate changes, a compensation correction calculation is used to determine the rate of urea solution supplied by the metering pump, so as to minimize the dynamic response error between the rate of urea solution ejected from the air-assisted nozzle and the rate of urea injection demand, and to make the error between the urea solution demand and the actual urea solution disappear as soon as possible. This method can effectively solve the problem of response lag between the rate of urea solution supplied by the metering pump and the rate of urea solution ejected from the nozzle in the air-assisted urea injection system, and avoid insufficient or excessive urea participating in the catalytic reduction reaction. Attached Figure Description

[0027] Figure 1This is a response lag compensation method for a urea solution injection system in the embodiments;

[0028] Figure 2 This is a schematic diagram of a gas-assisted urea solution injection system in one embodiment;

[0029] Figure 3 A graph showing the changes in urea injection demand flow rate and urea liquid flow rate ejected from the air-assisted atomizing nozzle before adding response compensation;

[0030] Figure 4 The graph shows the changes in urea injection demand flow rate and urea liquid flow rate ejected from the air-assisted atomizing nozzle after adding response compensation. Detailed Implementation

[0031] As described in the background art, given the lag between the rate of urea solution supplied by the metering pump and the rate of urea solution ejected from the air-assisted nozzle in an air-assisted urea injection system, this invention provides a method for compensating for the lag in a urea solution injection system. This method is based on a urea solution injection system, which includes at least a urea metering pump and an air source. The urea metering pump and the air source are respectively connected to a mixing chamber, which is connected to an air-assisted atomizing nozzle via a urea pipe. The method includes the following steps:

[0032] Step 1: Set the amount of residual urea solution in the urea tube to R, and construct a first-order dynamic system model for the amount of residual urea solution in the urea tube to correlate the rate at which the air-assisted atomizing nozzle sprays urea solution with the rate at which the metering pump pumps urea solution.

[0033] Step 2: Set the current residual urea solution volume in the urea tube to R = R1. At the current time t1, the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as: X1 = R1 / Tc, where Tc is the time constant in the first-order dynamic system model. The current rate at which the metering pump ejects urea solution is Y1. Then, the imbalance difference between the rate at which the metering pump ejects urea solution and the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as:

[0034] DX1 = Y1 - X1;

[0035] Step 3: Based on the first-order dynamic system model, calculate the velocity X2 of urea solution ejected from the air-assisted atomizing nozzle at time t2, expressed as:

[0036] R2=R1+Tc*DX1*(1-exp(-(t2-t1) / Tc))

[0037] X2=R2 / Tc=X1+DX1*(1-exp(-(t2-t1) / Tc))

[0038] Where R2 is the amount of residual urea solution in the urea tube at the next moment, and exp is an exponential function with the natural constant e as the base.

[0039] Step 4: Based on the actual operating conditions of the engine, the required urea injection rate at the next moment t2 is given as Xneed. The urea pumping rate at the next moment t2 is expressed as Y2 = Xneed + (Xneed - X2) * Ac, where Ac is the difference correction coefficient in the first-order power system model. The urea pumping rate at the next moment t2 is corrected to the calculated Y2 for compensation. The difference correction coefficient Ac can be set within the preset error allowable range, taking into account the actual structural characteristics of the urea injection system, so that the urea flow rate sprayed by the air-assisted atomizing nozzle can more quickly approach the required injection amount.

[0040] Specifically, in the embodiment, considering that the main mechanism of response lag is the flow time of the two-phase flow inside the pipe and the adhesion of urea liquid to the inner wall of the pipe, and since the compressed air flow velocity inside the urea pipe is generally greater than 10m / s, the flow time lag should be on the order of hundreds of milliseconds, while the lag caused by the adhesion of urea liquid to the inner wall of the pipe is on the order of several seconds, and is related to the magnitude of Y.

[0041] In step 1, the amount of residual urea solution in the urea tube is determined to be R. A first-order dynamic system model of the amount of residual urea solution in the urea tube is constructed to correlate the rate at which the urea solution is sprayed out by the air-assisted atomizing nozzle with the rate at which the urea solution is pumped out by the metering pump. The amount of urea adhering in the urea tube is affected by the rate of the urea solution. If the pipe is smooth or the fluid is non-viscous, the velocity at each point on the cross section of the pipe should be equal. However, in actual applications, the inner wall of the pipe is rough and the urea solution is also viscous, which will cause a gradient change in the flow velocity from the center of the pipe to the pipe wall. The fluid velocity close to the pipe wall is very small, or even tends to be 0. The higher the velocity, the greater the pressure at the same location inside the pipe, and the more liquid adheres to the pipe. Assuming the urea solution ejected from the gas-assisted nozzle is ejected at a velocity X = R / Tc, where X is in g / s or mL / s and Tc (in s) is the time constant of a first-order kinetic system model. Similar system parameters can be obtained through calibration or experimentation, a common practice in exhaust aftertreatment and even vehicle engine design. According to the law of conservation of mass, in future time t, the changes in R(t) and X(t) should satisfy the following first-order kinetic system model, expressed as:

[0042] (YX(t))dt=dR(t)

[0043] Where Y is the rate at which the metering pump supplies urea solution, X(t) represents the rate at which the urea solution is ejected from the air-assisted nozzle as a function of time t, d represents the integral, and R(t) represents the amount of residual urea solution R in the urea tube as a function of time t.

[0044] Substituting X(t)=R(t) / Tc into the equation, Tc is the time constant, which reflects the inertia of the system. The larger the time constant Tc is, the greater the inertia of the system and the slower the response speed. Tc is related to the characteristics of the system itself, such as the diameter, length, and material of the urea tube. Moreover, the time constant Tc is a basic parameter of a first-order dynamic system.

[0045] Solving for the given information yields:

[0046] R(t)=R0+Tc*(Y-X0)*(1-exp(-t / Tc))

[0047] X(t)=X0+(Y-X0)*(1-exp(-t / Tc))

[0048] R0 represents the initial amount of residual urea solution in the urea tube, and X0 represents the initial rate at which urea solution is ejected from the air-assisted atomizing nozzle.

[0049] The above equation indicates that when t >> Tc, X → Y; however, for a control system, it is desirable for the speed of X → Y to be as fast as possible, i.e., the time should be as short as possible. Therefore, for example, if at the next time t2, the system requires the urea injection rate to reach Xneed, and ABS(Xneed-X2) > 0, where ABS represents the absolute value function, then this can be achieved by correcting Y2 instead of taking Y2 = Xneed. An error correction coefficient Ac can be set, which can be obtained through calibration. We take Y2 = Xneed + (Xneed-X2) * Ac, where t2 is any time after the change in injection quantity, and is an evaluation index of the first-order system response speed. The smaller t2 is, the faster the response speed. For a first-order dynamic system, the system is tested, and the supply quantity is compensated within the allowable error range.

[0050] In step 2, assuming the current residual urea solution in the urea tube is R = R1, and the rate at which the air-assisted atomizing nozzle ejects urea solution at the current time t1 is expressed as: X1 = R1 / Tc, and the current rate at which the metering pump ejects urea solution is Y1, then the imbalance between the rate at which the metering pump ejects urea solution and the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as:

[0051] DX1 = Y1 - X1;

[0052] In step 3, based on the first-order dynamic system model, the velocity X2 of urea solution ejected from the air-assisted atomizing nozzle at time t2 is calculated and expressed as:

[0053] R2=R1+Tc*DX1*(1-exp(-(t2-t1) / Tc)),

[0054] X2=R2 / Tc=X1+DX1*(1-exp(-(t2-t1) / Tc)),

[0055] In step 4, based on the actual operating conditions of the engine, the required urea injection rate for the next time t2 is given as Xneed. Combined with X2 calculated in step 3, the urea pumping rate of the metering pump at the next time t2 is expressed as Y2 = Xneed + (Xneed - X2) * Ac. The urea pumping rate of the metering pump at the next time t2 is corrected to the calculated Y2 for compensation.

[0056] In one embodiment of the present invention, if the residual urea liquid volume R in the urea tube is negative, R (i.e., R1 or R2) is forced to be 0; if X2 is negative, X2 is forced to be 0; if Y2 is negative, Y2 is forced to be 0. The settings of parameters such as R, X2, and Y2 are related to the actual working conditions, system parameter limits, etc. For example, R represents the residual urea liquid volume in the urea tube, X2 represents the rate at which the air-assisted atomizing nozzle sprays urea liquid, and Y2 represents the rate at which the metering pump pumps urea liquid at any given time, which cannot be negative.

[0057] In one embodiment of the present invention, if ABS((Xneed-X2) / Xneed) is less than the preset error allowable value Err_limit, in order to prevent jetting oscillation caused by correction, Y2 = Xneed is forcibly taken. Err_limit is the post-processing product standard, which represents the error allowable value and is related to the accuracy of the post-processing system.

[0058] In one embodiment of the present invention, if the calculated Y2 is greater than the maximum injection rate Dose_max of the urea metering pump, then Y2 = Dose_max is forcibly taken. The actual injection efficiency at any time must be within the hardware allowable range. An injection rate exceeding the hardware capability range is meaningless. Therefore, the rate at which the metering pump pumps out urea liquid Y2 at any time cannot exceed the maximum injection rate of the system.

[0059] In one embodiment of the present invention, if (t2-t1) is much smaller than Tc, in step 3, the amount of residual urea liquid in the urea tube at the next moment is R2 = R1 + (t2-t1) * DX1, and the rate at which the air-assisted atomizing nozzle sprays urea liquid at the next moment t2 is X2 = R2 / Tc = X1 + (t2-t1) * DX1 / Tc.

[0060] See Figure 2In an embodiment of the present invention, an air-assisted urea liquid injection system is also provided, including a urea metering pump 1 and an air source 2. The urea metering pump 1 and the air source 2 are respectively connected to a mixing chamber 3. The mixing chamber 3 is connected to an air-assisted atomizing nozzle 5 through a urea pipe 4. The urea liquid pumped out by the urea metering pump 1 and the compressed air from the air source 2 enter the mixing chamber 3 successively and mix. The air-urea gas-liquid two-phase flow formed by the mixture flows through the urea pipe 4 to the air-assisted atomizing nozzle 5. The urea metering pump 1 is connected to a controller 6. The controller 6 executes the response lag compensation method of the air-assisted urea liquid injection system in the above embodiment. Starting from t1 = 0, it calculates the R2 and Y2 of the next time t2 and the new Xneed based on the known R1 and Y1 at the current time. It iteratively obtains the urea liquid pumping rate Y2 of the metering pump at any time, which will make the urea liquid spraying rate X2 of the air-assisted atomizing nozzle approach the required urea liquid injection rate Xneed more quickly.

[0061] Based on the above theory, taking steady-state operating conditions as an example, the changes in urea injection demand flow rate and urea liquid flow rate ejected from the air-assisted atomizing nozzle before and after adding response compensation are compared. The results are as follows: Figure 3 and Figure 4 As shown, Figure 3 This describes the typical characteristics of injection response hysteresis when the system is operating normally without response compensation. Figure 4 To improve the injection response characteristics after response compensation, a comparison shows that under normal system conditions, without response compensation, there is a deviation between curve A (urea injection demand flow rate) and curve B (urea liquid flow rate from the air-assisted atomizing nozzle). Especially when the urea injection demand flow rate changes abruptly, the dynamic change in the urea liquid flow rate from the air-assisted atomizing nozzle deteriorates significantly. However, after adding response compensation, the following performance of the urea liquid flow rate from the air-assisted atomizing nozzle is greatly improved in both curves A and B, thus approaching the required injection volume more quickly.

[0062] This invention establishes a physical model between the flow rate of urea solution ejected from the air-assisted atomizing nozzle and the flow rate of urea solution supplied by the metering pump, and obtains a difference correction coefficient. This allows the metering pump to determine the flow rate of urea solution supplied when the required urea injection flow rate changes, through a compensation and correction calculation. This minimizes the dynamic response error between the flow rate of urea solution ejected from the air-assisted nozzle and the required urea injection flow rate, effectively solving the problem of response lag between the flow rate of urea solution supplied by the metering pump and the flow rate of urea solution ejected from the nozzle in the air-assisted urea injection system.

[0063] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0064] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for compensating for response lag in a urea solution injection system, comprising a urea metering pump and an air source, wherein the urea metering pump and the air source are respectively connected to a mixing chamber, and the mixing chamber is connected to an air-assisted atomizing nozzle via a urea pipe, characterized in that, The method includes the following steps: Step 1: Set the amount of residual urea solution in the urea tube to R, and construct a first-order dynamic system model for the amount of residual urea solution in the urea tube to correlate the rate at which the air-assisted atomizing nozzle sprays urea solution with the rate at which the metering pump pumps urea solution. Step 2: Set the current residual urea solution volume in the urea tube to R=R1. At the current time t1, the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as: X1=R1 / Tc, where Tc is the time constant in the first-order dynamic system model. The current rate at which the metering pump ejects urea solution is Y1. Then, the imbalance difference between the rate at which the metering pump ejects urea solution and the rate at which the air-assisted atomizing nozzle ejects urea solution is expressed as: DX1 = Y1 - X1; Step 3: Based on the first-order dynamic system model, calculate the velocity X2 of urea solution ejected from the air-assisted atomizing nozzle at time t2, expressed as: R2=R1+Tc*DX1*(1-exp(-(t2-t1) / Tc)) X2=R2 / Tc=X1+ DX1*(1-exp(-(t2-t1) / Tc)) Where R2 is the amount of residual urea solution in the urea tube at the next moment, and exp is an exponential function with the natural constant e as the base. Step 4: Based on the actual operating conditions of the engine, the required urea injection rate at the next time t2 is given as Xneed. The urea pumping rate at the next time t2 is expressed as Y2=Xneed+(Xneed-X2)*Ac, where Ac is the difference correction coefficient in the first-order dynamic system model. The urea pumping rate at the next time t2 is corrected to the calculated Y2 for compensation.

2. The response hysteresis compensation method for a urea solution injection system according to claim 1, characterized in that: The constructed first-order dynamic system model of the amount of residual urea solution in the urea tube is expressed as follows: (YX(t))dt=dR(t) Where Y is the rate at which the metering pump supplies urea solution, X(t) represents the rate at which the urea solution is ejected from the air-assisted nozzle as a function of time t, d represents the integral, and R(t) represents the amount of residual urea solution R in the urea tube as a function of time t. Substituting X(t) = R(t) / Tc into the equation, where Tc is the time constant, we can solve for: R(t)=R0+Tc*(Y-X0)*(1-exp(-t / Tc)) X(t)=X0+(Y-X0)*(1-exp(-t / Tc)) R0 represents the initial amount of residual urea solution in the urea tube, and X0 represents the initial rate at which urea solution is ejected from the air-assisted atomizing nozzle.

3. The response hysteresis compensation method for a urea solution injection system according to claim 1, characterized in that: If the residual urea solution R in the urea tube is negative, take R=0; if X2 is negative, take X2=0; if Y2 is negative, take Y2=0.

4. The response hysteresis compensation method for a urea solution injection system according to claim 1, characterized in that: If there exists ABS((Xneed-X2) / Xneed) less than the preset error tolerance value Err_limit, then Y2=Xneed, where Err_limit is the post-processing product standard, representing the error tolerance value.

5. The response lag compensation method for a urea solution injection system according to claim 1, characterized in that: If the calculated Y2 is greater than the maximum injection rate Dose_max of the urea metering pump, then Y2 = Dose_max.

6. The response hysteresis compensation method for a urea solution injection system according to claim 1, characterized in that: If (t2-t1) is much smaller than Tc, in step 3, the amount of residual urea liquid in the urea tube at the next moment is R2=R1+(t2-t1)*DX1, and the rate at which the air-assisted atomizing nozzle sprays urea liquid at the next moment t2 is X2=R2 / Tc=X1+(t2-t1)*DX1 / Tc.

7. A gas-assisted urea liquid injection system, comprising a urea metering pump and an air source, wherein the urea metering pump and the air source are respectively connected to a mixing chamber, the mixing chamber is connected to a gas-assisted atomizing nozzle through a urea pipe, the urea liquid pumped by the urea metering pump and the compressed air from the air source enter the mixing chamber sequentially and mix, the mixed air-urea gas-liquid two-phase flow flows through the urea pipe to the gas-assisted atomizing nozzle, the urea metering pump is connected to a controller, the controller executes the response hysteresis compensation method of the urea liquid injection system according to claim 1, and controls the gas-assisted atomizing nozzle to inject urea liquid.

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