Two-stage SCR configuration preceding-stage SCR closed-loop control method

Abstract

The invention discloses a two-stage SCR configuration preceding-stage SCR closed-loop control method, relates to the field of SCR control, and solves the technical problems that NOx emission control is inaccurate, urea consumption is too high, N2O emission is high and the ammonia leakage risk is increased due to the fact that the urea injection amount cannot be adjusted in real time in a traditional open-loop control method. The method comprises the steps of setting a preceding-stage SCR closed-loop control triggering condition, obtaining a preceding-stage SCR closed-loop control triggering parameter, judging whether the preceding-stage SCR closed-loop control triggering condition is met or not according to the preceding-stage SCR closed-loop control triggering parameter, and when the preceding-stage SCR closed-loop control triggering condition is met, obtaining a conversion efficiency deviation e (t), pID control is carried out on the conversion efficiency deviation e (t) to obtain a urea injection amount correction coefficient u (t), and the urea injection amount is corrected according to the urea injection amount correction coefficient u (t). According to the method, efficient NOx emission control is achieved, and NOx emission under cold start and low load working conditions is reduced.

Description

Technical Field

[0001] The present invention relates to the field of SCR, and more particularly to a closed-loop control method for a front-stage SCR in a dual-stage SCR configuration. Background Art

[0002] The dual-stage SCR aftertreatment system is a highly effective exhaust treatment technology widely used in heavy-duty diesel engines to meet stricter emission standards. The closed-loop control logic of the pre-stage SCR is critical to ensuring the efficient operation of the entire aftertreatment system. Traditional open-loop control methods cannot adjust the urea injection rate in real time, resulting in inaccurate NOx emission control, excessive urea consumption, high N2O emissions, and increased risk of ammonia slip. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a closed-loop control method for the front-stage SCR of a two-stage SCR configuration, so as to solve the technical problems that the traditional open-loop control method cannot adjust the urea injection amount in real time, resulting in inaccurate NOx emission control, excessive urea consumption, high N2O emissions, and increased ammonia leakage risk.

[0004] The present invention provides a method for closed-loop control of a front-stage SCR in a dual-stage SCR configuration, comprising setting a trigger condition for closed-loop control of the front-stage SCR, obtaining a trigger parameter for closed-loop control of the front-stage SCR, and determining whether the trigger condition for closed-loop control of the front-stage SCR is met based on the trigger parameter for closed-loop control of the front-stage SCR;

[0005] When the pre-stage SCR closed-loop control trigger condition is met, the conversion efficiency deviation e(t) is obtained, the conversion efficiency deviation e(t) is subjected to PID control to obtain a urea injection amount correction coefficient u(t), and the urea injection amount is corrected according to the urea injection amount correction coefficient u(t).

[0006] As a further improvement, the method for obtaining the conversion efficiency deviation e(t) is:

[0007] The outlet NOx concentration and the inlet NOx concentration are obtained, the measured NOx conversion efficiency is calculated based on the outlet NOx concentration and the inlet NOx concentration, the model NOx conversion efficiency is calibrated based on the outlet NOx concentration and the inlet NOx concentration, and the conversion efficiency deviation e(t) is obtained by subtracting the measured NOx conversion efficiency from the model NOx conversion efficiency.

[0008] Furthermore, the expression for the measured NOx conversion efficiency is calculated based on the outlet NOx concentration and the inlet NOx concentration:

[0009] η 实测NOx =(1-C 出口NOx / C 入口NOx)×100%;

[0010] Among them, η 实测NOx is the measured NOx conversion efficiency, C 出口NOx is the outlet NOx concentration, C 入口NOx is the inlet NOx concentration.

[0011] Furthermore, the expression of the urea injection amount correction coefficient u(t) obtained by performing PID control according to the conversion efficiency deviation e(t) is:

[0012]

[0013] Among them, K p is the proportional gain, T i is the integral time constant, Td is the differential time constant, t is the front-stage NOx efficiency deviation correction time, dt is the front-stage NOx efficiency deviation integral time, t is the front-stage NOx efficiency deviation correction time, and de(t) is the front-stage NOx efficiency deviation differential time.

[0014] Furthermore, after the urea injection amount correction coefficient u(t) is calculated, it is determined whether the urea injection amount correction coefficient u(t) is available. If so, the urea injection amount is corrected using the urea injection amount correction coefficient u(t). Otherwise, an injection coefficient reset determination is performed.

[0015] Furthermore, the method for determining whether the urea injection amount correction coefficient u(t) is available is:

[0016] When the urea injection amount correction coefficient u(t) is greater than or equal to a preset minimum correction coefficient and less than or equal to a preset maximum correction coefficient, it is determined that the urea injection amount correction coefficient u(t) is available.

[0017] Furthermore, the injection coefficient reset judgment is to reset the urea injection amount correction coefficient u(t) to one when the urea injection amount correction coefficient u(t) is greater than a preset correction coefficient threshold and the ammonia leakage value under the reverse drag condition is greater than a preset ammonia leakage threshold.

[0018] Furthermore, when the closed-loop control triggering condition of the front-stage SCR is not satisfied, open-loop control is performed on the front-stage SCR.

[0019] Furthermore, the pre-stage SCR closed-loop control trigger parameters include urea injection status, pre-stage SCR bed temperature, pre-stage SCR efficiency actual value, pre-stage SCR efficiency model value, engine operating mode, pre-stage and post-stage NOx sensor signals, DPF upstream temperature, SCR efficiency, pre-stage SCR passive regeneration injection coefficient and pre-stage SCR system fault status.

[0020] Furthermore, the triggering conditions of the front-stage SCR closed-loop control include:

[0021] First condition: the urea injection state is the injection state;

[0022] Second condition: the front-stage SCR bed temperature is greater than the preset maximum bed temperature and less than the preset minimum bed temperature;

[0023] Third condition: the absolute value of the difference between the measured value of the front-stage SCR efficiency and the model value of the front-stage SCR efficiency is greater than a preset set deviation value;

[0024] Fourth condition: the engine operating mode is normal mode or heating mode;

[0025] Fifth condition: the signals from the upstream and downstream NOx sensors are both valid signals;

[0026] Sixth condition: the DPF upstream temperature is less than or equal to a preset set temperature value;

[0027] Seventh condition: the SCR efficiency is greater than a preset minimum efficiency;

[0028] Condition 8: The passive regeneration injection coefficient of the front-stage SCR is greater than or equal to a preset set injection coefficient;

[0029] Ninth condition: the non-pre-stage SCR system fault state is a non-fault triggering state.

[0030] Beneficial effects

[0031] The advantages of the present invention are:

[0032] The present invention sets a pre-stage SCR closed-loop control trigger condition, obtains a pre-stage SCR closed-loop control trigger parameter, determines whether the pre-stage SCR closed-loop control trigger condition is met according to the pre-stage SCR closed-loop control trigger parameter, obtains a conversion efficiency deviation when the pre-stage SCR closed-loop control trigger condition is met, performs PID control on the conversion efficiency deviation to obtain a urea injection amount correction coefficient, and corrects the urea injection amount according to the urea injection amount correction coefficient, thereby achieving precise urea consumption control, reducing excessive urea injection, and reducing operating costs; reducing the risk of ammonia leakage, avoiding excessive NH3 caused by overspray of urea, thereby reducing the generation of a large amount of N2O after NH3 leaks into the DOC, and reducing greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of the front-stage SCR closed-loop control of the present invention;

[0034] Figure 2 Schematic diagram of the release condition of the front-stage SCR closed-loop control of the present invention;

[0035] Figure 3 This is a flow chart of the front-stage SCR closed-loop control method of the present invention;

[0036] Figure 4 This is a flow chart of the front-stage SCR closed loop and closed loop reset control of the present invention;

[0037] Figure 5 Schematic diagram of the bipolar SCR post-processing structure of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the embodiments, but this does not constitute any limitation to the present invention. Any limited number of modifications made by anyone within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0039] See Figure 1-Figure 5 A method for closed-loop control of a front-stage SCR in a dual-stage SCR configuration is disclosed. The method includes setting a trigger condition for the closed-loop control of the front-stage SCR and obtaining trigger parameters for the closed-loop control of the front-stage SCR. The trigger parameters for the closed-loop control of the front-stage SCR include urea injection status, front-stage SCR bed temperature, measured value of front-stage SCR efficiency, model value of front-stage SCR efficiency, engine operating mode, front-stage and rear-stage NOx sensor signals, DPF upstream temperature, SCR efficiency, front-stage SCR passive regeneration injection coefficient, and a system fault status without the front-stage SCR.

[0040] Whether the pre-stage SCR closed-loop control triggering conditions are met is determined based on the urea injection status, pre-stage SCR bed temperature, pre-stage SCR efficiency measured value, pre-stage SCR efficiency model value, engine operation mode, pre-stage and post-stage NOx sensor signals, DPF upstream temperature, SCR efficiency, pre-stage SCR passive regeneration injection coefficient and pre-stage SCR system fault status. When the pre-stage SCR closed-loop control triggering conditions are met, the pre-stage SCR closed-loop control strategy is triggered.

[0041] like Figure 2 As shown, the triggering conditions of the front-stage SCR closed-loop control include:

[0042] First condition: the urea injection state is the injection state.

[0043] Second condition: the front-stage SCR bed temperature is greater than the preset maximum bed temperature and less than the preset minimum bed temperature.

[0044] Third condition: the absolute value of the difference between the actual measured value of the front-stage SCR efficiency and the model value of the front-stage SCR efficiency is greater than a preset set deviation value.

[0045] Fourth condition: the engine operating mode is normal mode or heating mode.

[0046] Fifth condition: The signals from the upstream and downstream NOx sensors are both valid.

[0047] Sixth condition: the DPF upstream temperature is less than or equal to a preset set temperature value.

[0048] Seventh condition: The SCR efficiency is greater than the preset minimum efficiency.

[0049] Eighth condition: the front-stage SCR passive regeneration injection coefficient is greater than or equal to the preset set injection coefficient.

[0050] Ninth condition: There is no fault state of the front-stage SCR system, which is a no-fault trigger state.

[0051] Meeting the above nine conditions at the same time means that the triggering conditions for the front-stage SCR closed-loop control are met.

[0052] like Figure 3 As shown, the closed-loop control strategy of the front-stage SCR is:

[0053] The conversion efficiency deviation e(t) is obtained by obtaining the outlet NOx concentration and the inlet NOx concentration, and calculating the measured NOx conversion efficiency based on the outlet NOx concentration and the inlet NOx concentration. The expression for calculating the measured NOx conversion efficiency based on the outlet NOx concentration and the inlet NOx concentration is:

[0054] η 实测NOx =(1-C 出口NOx / C 入口NOx )×100%;

[0055] Among them, η 实测NOx is the measured NOx conversion efficiency, C 出口NOx is the outlet NOx concentration, C 入口NOx is the inlet NOx concentration.

[0056] The model NOx conversion efficiency is calibrated according to the outlet NOx concentration and the inlet NOx concentration, and the conversion efficiency deviation e(t) is obtained by subtracting the measured NOx conversion efficiency from the model NOx conversion efficiency.

[0057] For example, η 实测NOx =80%, the calibrated model NOx conversion efficiency is 85%, and the conversion efficiency deviation e(t) is 5%.

[0058] The urea injection amount correction coefficient is obtained by performing PID control according to the conversion efficiency deviation e(t). The expression of the urea injection amount correction coefficient is as follows:

[0059]

[0060] Among them, Kp is the proportional gain, T i is the integral time constant, Td is the differential time constant, dt is the front-stage NOx efficiency deviation integral time, t is the front-stage NOx efficiency deviation correction time, and de(t) is the front-stage NOx efficiency deviation differential time.

[0061] like Figure 4 As shown, after the urea injection amount correction coefficient u(t) is calculated, it is determined whether the urea injection amount correction coefficient u(t) is available. If so, the urea injection amount is corrected using the urea injection amount correction coefficient u(t). Otherwise, the injection coefficient reset judgment is executed.

[0062] The method to determine whether the urea injection amount correction coefficient u(t) is available is:

[0063] When the urea injection amount correction coefficient u(t) is greater than or equal to a preset minimum correction coefficient and less than or equal to a preset maximum correction coefficient, it is determined that the urea injection amount correction coefficient u(t) is available.

[0064] The injection coefficient reset judgment is that when the urea injection amount correction coefficient u(t) is greater than a preset correction coefficient threshold and the ammonia leakage value under the reverse drag condition is greater than the preset ammonia leakage threshold, the urea injection amount correction coefficient u(t) is reset to one.

[0065] The urea injection amount is corrected according to the urea injection amount correction coefficient.

[0066] When the closed-loop control triggering condition of the front-stage SCR is not met, open-loop control is performed on the front-stage SCR.

[0067] Efficient NOx emission control: Pre-SCR urea injection significantly reduces NOx emissions during cold start and low-load conditions. The pre-SCR closed-loop control logic dynamically adjusts the urea injection rate based on real-time monitoring data to ensure NOx emissions remain within a predetermined range.

[0068] Urea consumption control: By precisely controlling the urea injection amount, excessive urea injection is reduced, thus lowering operating costs, while increasing the urea injection amount can reduce emissions.

[0069] Ammonia leakage control: By precisely controlling the urea injection rate, the risk of ammonia leakage is reduced. This prevents excessive NH3 levels from leaking into the DOC and generating large amounts of N2O, thereby reducing greenhouse gas emissions.

[0070] DPF Passive Regeneration Control: Incorporating pre-SCR closed-loop control logic within appropriate SCR and DPF temperature ranges reduces cold-start, low-load NOx emissions while ensuring ammonia leakage and the DPF's passive regeneration capability. The passive regeneration closed loop activates at low DPF temperatures and shuts down at high temperatures to ensure DPF passive regeneration efficiency.

[0071] like Figure 5 As shown, the first output end of the urea injection device is directed toward the first SCR / ASC, and the second output end of the urea injection device is directed toward the second SCR / ASC.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the structure of the present invention. These modifications and improvements will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A closed-loop control method for the front-stage SCR of a two-stage SCR configuration, characterized in that: The method comprises setting a pre-stage SCR closed-loop control trigger condition, obtaining a pre-stage SCR closed-loop control trigger parameter, and determining whether the pre-stage SCR closed-loop control trigger condition is met according to the pre-stage SCR closed-loop control trigger parameter; When the pre-stage SCR closed-loop control trigger condition is met, a conversion efficiency deviation e(t) is obtained, PID control is performed on the conversion efficiency deviation e(t) to obtain a urea injection amount correction coefficient u(t), and the urea injection amount is corrected according to the urea injection amount correction coefficient u(t).

2. A closed-loop control method for the front-stage SCR of a two-stage SCR configuration according to claim 1, characterized in that: The method for obtaining the conversion efficiency deviation e(t) is: The outlet NOx concentration and the inlet NOx concentration are obtained, the measured NOx conversion efficiency is calculated based on the outlet NOx concentration and the inlet NOx concentration, the model NOx conversion efficiency is calibrated based on the outlet NOx concentration and the inlet NOx concentration, and the conversion efficiency deviation e(t) is obtained by subtracting the measured NOx conversion efficiency from the model NOx conversion efficiency.

3. The closed-loop control method for the front-stage SCR of a dual-stage SCR configuration according to claim 2, characterized in that: The expression for the measured NOx conversion efficiency calculated based on the outlet NOx concentration and the inlet NOx concentration is: or 实测NOx =(1-C 出口NOx / C 入口NOx )×100%; Among them, η 实测NOx is the measured NOx conversion efficiency, C 出口NOx is the outlet NOx concentration, C 入口NOx is the inlet NOx concentration.

4. The closed-loop control method for the front-stage SCR of a dual-stage SCR configuration according to claim 1, characterized in that: The expression of the urea injection amount correction coefficient u(t) obtained by performing PID control according to the conversion efficiency deviation e(t) is: Among them, K p is the proportional gain, T i is the integral time constant, Td is the differential time constant, dt is the front-stage NOx efficiency deviation integral time, t is the front-stage NOx efficiency deviation correction time, and de(t) is the front-stage NOx efficiency deviation differential time.

5. The closed-loop control method for the front-stage SCR of a two-stage SCR configuration according to claim 1, characterized in that: After the urea injection amount correction coefficient u(t) is calculated, it is determined whether the urea injection amount correction coefficient u(t) is available. If so, the urea injection amount is corrected using the urea injection amount correction coefficient u(t). Otherwise, an injection coefficient reset determination is performed.

6. The method for closed-loop control of the front-stage SCR of a dual-stage SCR configuration according to claim 5, characterized in that: The method for judging whether the urea injection amount correction coefficient u(t) is applicable is: When the urea injection amount correction coefficient u(t) is greater than or equal to a preset minimum correction coefficient and less than or equal to a preset maximum correction coefficient, it is determined that the urea injection amount correction coefficient u(t) is available.

7. The closed-loop control method for the front-stage SCR of a two-stage SCR configuration according to claim 5, characterized in that: The injection coefficient reset judgment is to reset the urea injection amount correction coefficient u(t) to one when the urea injection amount correction coefficient u(t) is greater than a preset correction coefficient threshold and the ammonia leakage value under the reverse drag condition is greater than a preset ammonia leakage threshold.

8. The closed-loop control method for the front-stage SCR of a dual-stage SCR configuration according to claim 1, characterized in that: When the closed-loop control triggering condition of the front-stage SCR is not met, open-loop control is performed on the front-stage SCR.

9. The closed-loop control method for the front-stage SCR of a dual-stage SCR configuration according to claim 1, characterized in that: The pre-stage SCR closed-loop control trigger parameters include urea injection status, pre-stage SCR bed temperature, pre-stage SCR efficiency measured value, pre-stage SCR efficiency model value, engine operation mode, pre-stage and post-stage NOx sensor signals, DPF upstream temperature, SCR efficiency, pre-stage SCR passive regeneration injection coefficient and pre-stage SCR system fault status.

10. The closed-loop control method for the front-stage SCR of a dual-stage SCR configuration according to claim 9, characterized in that: The trigger conditions for the front-stage SCR closed-loop control include: First condition: the urea injection state is the injection state; Second condition: the front-stage SCR bed temperature is greater than the preset maximum bed temperature and less than the preset minimum bed temperature; Third condition: the absolute value of the difference between the measured value of the front-stage SCR efficiency and the model value of the front-stage SCR efficiency is greater than a preset set deviation value; Fourth condition: the engine operating mode is normal mode or heating mode; Fifth condition: the signals from the upstream and downstream NOx sensors are both valid signals; Sixth condition: the DPF upstream temperature is less than or equal to a preset set temperature value; Seventh condition: the SCR efficiency is greater than a preset minimum efficiency; Condition 8: The passive regeneration injection coefficient of the front-stage SCR is greater than or equal to a preset set injection coefficient; Ninth condition: the non-pre-stage SCR system fault state is a non-fault triggering state.

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