A NOx based on ammonia storage synergy x and N2O emission suppression control methods

Abstract

The present invention discloses a NOx-based x The invention relates to a method for suppressing N2O emissions, which involves post-processing, dynamically adjusting the ammonia storage capacity of each SCR stage according to the exhaust temperature and conversion efficiency of the dual-stage SCR, and injecting an equivalent amount of urea to the front end of each SCR stage according to the ammonia storage capacity. The invention realizes the precise injection of urea and achieves a balanced NO x Conversion efficiency, in reducing NO x The purpose is to reduce emissions and suppress the generation of N2O.

Description

Technical Field

[0001] The present invention relates to post-treatment, more particularly, it relates to a NO x and N2O emission suppression control methods. Background Art

[0002] The greenhouse effect of N2O is 300 times that of CO2, so Euro 7 has clear limit requirements for N2O gas emitted by vehicles. Figure 1 The figure shows the relationship between the N2O generation rate and temperature. N2O is mainly generated by the reaction of NO or NO2 with NH3. The temperature range of 200-280℃ is the main area for the generation of N2O. In post-treatment technology, the basic principle of selective catalytic reduction is to add the reducing agent NH3 to the exhaust gas and use a suitable catalyst to promote the reaction of the reducing agent with NO. x The SCR system can effectively reduce NOx emissions by inhibiting the non-selective oxidation reaction of the reducing agent and oxygen. However, as the amount of NH3 injection increases in the SCR system, a side reaction occurs in the SCR catalyst to produce greenhouse gas N2O. In order to further suppress the NOx and N2O emissions in the exhaust gas of vehicles with a dual-stage SCR system, we provide a method that can suppress NO in the engine after-treatment process. x and control methods for N2O generation. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a NO x and N2O emission suppression control methods, achieving a balance of NO x Conversion efficiency, in reducing NO x The purpose is to reduce emissions and suppress the generation of N2O.

[0004] The present invention discloses a NO based on ammonia storage synergy x and a N2O emission suppression control method, which dynamically adjusts the ammonia storage amount of each SCR stage according to the exhaust temperature and conversion efficiency of the dual-stage SCR, and injects an equivalent amount of urea to the front end of each SCR stage according to the ammonia storage amount.

[0005] Further improvements are made to obtain the conversion efficiency of the front-stage SCR and the exhaust temperature of the rear-stage SCR;

[0006] When the conversion efficiency of the front-stage SCR is greater than or equal to a set first conversion threshold, and the exhaust temperature of the rear-stage SCR is greater than or equal to a set first temperature threshold, a dynamic negative correction is made to the ammonia storage amount of the front-stage SCR to reduce the ammonia storage amount of the front-stage SCR, and a dynamic positive correction is made to the ammonia storage amount of the rear-stage SCR to increase the ammonia storage amount of the rear-stage SCR;

[0007] When the conversion efficiency of the front-stage SCR is greater than or equal to a set second conversion threshold, and the exhaust temperature of the rear-stage SCR is greater than or equal to a set second temperature threshold, a dynamic negative correction is performed on the ammonia storage amount of the front-stage SCR to reduce the ammonia storage amount of the front-stage SCR, and the ammonia storage amount of the rear-stage SCR is maintained at the current ammonia storage amount.

[0008] Furthermore, the dynamic negative correction is specifically:

[0009] Obtain a front-stage real-time ammonia storage value of the front-stage SCR, compare the front-stage real-time ammonia storage value with a set target ammonia storage value of the front-stage SCR to obtain a front-stage ammonia storage deviation value; obtain a front-stage predicted ammonia storage value of the front-stage SCR through an ammonia storage closed-loop calculation formula, and use the difference between the front-stage predicted ammonia storage value and the front-stage ammonia storage deviation value as the front-stage dynamic ammonia storage value after dynamic negative correction of the ammonia storage amount of the front-stage SCR.

[0010] Furthermore, the dynamic positive correction is specifically:

[0011] Obtain a post-stage real-time ammonia storage value of the post-stage SCR, compare the post-stage real-time ammonia storage value with a set target ammonia storage value of the post-stage SCR to obtain a post-stage ammonia storage deviation value; obtain a post-stage predicted ammonia storage value of the post-stage SCR through an ammonia storage closed-loop calculation formula, and use the sum of the post-stage predicted ammonia storage value and the post-stage ammonia storage deviation value as the post-stage dynamic ammonia storage value after dynamic positive correction of the ammonia storage amount of the post-stage SCR.

[0012] Furthermore, the ammonia storage closed-loop calculation formula is:

[0013]

[0014] Where n = 1 means that the closed-loop calculation formula for ammonia storage calculates the predicted ammonia storage value of the front stage, and n = 2 means that the closed-loop calculation formula for ammonia storage calculates the predicted ammonia storage value of the back stage; u(t n ) is the predicted ammonia storage value; Kp n is the proportional coefficient of urea injection amount based on ammonia storage deviation control; e(t) is the temperature deviation; dt n Ti is the urea injection amount integration time; n Td is the integral control time of urea injection amount; n is the differential control time of urea injection amount; de(t n ) is the differential time of urea injection amount; t is the regeneration temperature correction time; T is the differential correction time of urea injection amount deviation.

[0015] Furthermore, when the exhaust temperature of the rear-stage SCR is lower than a set first temperature threshold, the ammonia storage amount of the front-stage SCR is the target ammonia storage value, and the ammonia storage amount of the rear-stage SCR is maintained at the current ammonia storage amount.

[0016] Beneficial effects

[0017] The advantages of the present invention are: dynamically adjusting the ammonia storage capacity of each stage SCR according to the exhaust temperature and conversion efficiency of the two-stage SCR, and injecting an equivalent amount of urea to the front end of each stage SCR according to the ammonia storage capacity, thereby achieving precise injection of urea and achieving a balanced NO x Conversion efficiency, in reducing NO x The purpose is to reduce emissions and suppress the generation of N2O. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the relationship between N2O generation rate and temperature;

[0019] Figure 2 This is a configuration diagram of the dual-stage SCR post-treatment system of the present invention;

[0020] Figure 3 The NO of the present invention is opened and closed for hot WHTC cycle x Comparison of tail N2O concentration when using the N2O emission suppression control method. DETAILED DESCRIPTION

[0021] 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.

[0022] The present invention is a NO based on ammonia storage synergy x The N2O emission suppression control method dynamically adjusts the ammonia storage capacity of each SCR stage according to the exhaust temperature and conversion efficiency of the dual-stage SCR, and injects an equivalent amount of urea to the front end of each SCR stage according to the ammonia storage capacity, thereby achieving precise injection of urea and achieving balanced NO x Conversion efficiency, in reducing NO x The purpose of reducing emissions and suppressing the generation of N2O is to Figure 2 The figure shows a two-stage SCR post-processing configuration diagram on which the control method of the present invention relies. The specific process of the control method of the present invention is as follows.

[0023] Obtain the conversion efficiency of the front-stage SCR and the exhaust temperature of the rear-stage SCR. When the exhaust temperature of the rear-stage SCR is lower than the set first temperature threshold, the ammonia storage capacity of the front-stage SCR is the target ammonia storage value, and the ammonia storage capacity of the rear-stage SCR is maintained at the current ammonia storage capacity. If it is in the initial state, the ammonia storage capacity of the rear-stage SCR is also the target ammonia storage value of the rear-stage SCR. Among them, according to the working range temperature of the rear-stage SCR, the first temperature threshold can be set to 200°C. At this temperature, the rear-stage SCR is not the main temperature range for generating N2O, so the N2O generated by the overall SCR system is not obvious. The SCR system mainly catalyzes NO x The ammonia reserve of the SCR system does not need to be adjusted.

[0024] When the conversion efficiency of the front-stage SCR is greater than or equal to the set first conversion threshold, such as 90%, and the exhaust temperature of the rear-stage SCR is greater than or equal to the set first temperature threshold, it means that the temperatures of the two-stage SCR are the main temperature areas for generating N2O. At this time, the ammonia storage capacity of the front-stage SCR is dynamically negatively corrected to reduce the ammonia storage capacity of the front-stage SCR; at the same time, the ammonia storage capacity of the rear-stage SCR is dynamically positively corrected to increase the ammonia storage capacity of the rear-stage SCR. Under this operating condition, the conversion efficiency of the front-stage SCR is relatively high, so the urea injection amount of the front-stage SCR can be appropriately reduced. Through the efficient conversion of the front-stage SCR, the generation of N2O in the front-stage SCR can be reduced by reducing the ammonia storage capacity without reducing the conversion efficiency of NOx. However, this will cause the front-stage SCR to reduce the conversion efficiency of NOx. x The conversion of NO is reduced, and more NO x Therefore, in order to make the post-stage SCR able to adapt to the increased NO x By dynamically adjusting the ammonia storage amount to increase the urea injection amount of the subsequent SCR, the subsequent SCR can meet the needs of treating NO x Emission requirements. Since the amount of urea injected by the post-stage SCR is proportional to the amount of NO x Therefore, the problem of urea injected into the rear SCR causing more N2O generation can be avoided.

[0025] When the conversion efficiency of the front-stage SCR is greater than or equal to the set second conversion threshold, such as 50%, and the exhaust temperature of the rear-stage SCR is greater than or equal to the set second temperature threshold, such as 260°C, the ammonia storage capacity of the front-stage SCR is dynamically negatively corrected to reduce the ammonia storage capacity of the front-stage SCR and maintain the ammonia storage capacity of the rear-stage SCR at the current ammonia storage capacity. Among them, under the operating condition where the second conversion threshold is 50% and the second temperature threshold is 260°C, the conversion efficiency of the front-stage SCR is low, and there is a risk of excessive urea when injecting urea with the current ammonia storage capacity. Therefore, in order to reduce the generation of N2O in the front-stage SCR, appropriately reducing its ammonia storage capacity will not affect the front-stage SCR's response to NO x The final conversion amount of the single stage can effectively prevent the problem of excessive N2O generation caused by excessive urea injection in the front stage SCR. The ammonia storage amount of the rear stage SCR remains unchanged, so the generation of N2O and the conversion of NO x The conversion amount of NO remains unchanged, so overall, the dual-stage SCR achieves NO x Balance of conversion amount and suppression of N2O gas.

[0026] The above dynamic correction process will be introduced below.

[0027] Regarding dynamic negative correction, the specific correction process is as follows: obtain the real-time ammonia storage value of the front-stage SCR, compare the real-time ammonia storage value of the front-stage SCR with the set target ammonia storage value of the front-stage SCR to obtain the front-stage ammonia storage deviation value. Use the ammonia storage closed-loop calculation formula to obtain the front-stage predicted ammonia storage value of the front-stage SCR, and use the difference between the front-stage predicted ammonia storage value and the front-stage ammonia storage deviation value as the front-stage dynamic ammonia storage value after dynamic negative correction of the ammonia storage capacity of the front-stage SCR.

[0028] Regarding dynamic positive correction, the specific correction process is as follows: obtain the real-time ammonia storage value of the downstream SCR, compare the real-time ammonia storage value with the target ammonia storage value set for the downstream SCR to obtain the downstream ammonia storage deviation value. Use the ammonia storage closed-loop calculation formula to obtain the downstream predicted ammonia storage value of the downstream SCR, and use the sum of the downstream predicted ammonia storage value and the downstream ammonia storage deviation value as the downstream dynamic ammonia storage value after dynamic positive correction of the ammonia storage capacity of the downstream SCR.

[0029] The dynamic correction process described above combines the real-time ammonia storage value, the target ammonia storage value, and the predicted ammonia storage value obtained through closed-loop calculation to determine the final dynamic ammonia storage value. This dynamic ammonia storage value then determines the urea injection rate. This allows for dynamic adjustment of ammonia storage to varying conversion efficiencies and exhaust temperatures, thereby suppressing N2O formation.

[0030] In this embodiment, the closed-loop calculation formula for ammonia storage is:

[0031]

[0032] Where n = 1 means that the closed-loop calculation formula for ammonia storage calculates the predicted ammonia storage value of the front stage, and n = 2 means that the closed-loop calculation formula for ammonia storage calculates the predicted ammonia storage value of the back stage; u(t n ) is the predicted ammonia storage value; Kp n is the proportional coefficient of urea injection amount based on ammonia storage deviation control; e(t) is the temperature deviation; dt n Ti is the urea injection amount integration time; n Td is the integral control time of urea injection amount; n is the differential control time of urea injection amount; de(t n ) is the differential time of urea injection amount; t is the regeneration temperature correction time; T is the differential correction time of urea injection amount deviation.

[0033] like Figure 3 Shown is the hot WHTC cycle open and close this NO x The comparison chart of tail exhaust N2O concentration when using the N2O emission suppression control method is shown in Figure 2. Through the WHTC cycle test data analysis, when the engine is just started, the two-stage SCR system is in the low temperature area, so the N2O generation concentration is low. As the engine running time increases, when the temperature range reaches 200-280℃, the corresponding Figure 3 In the middle 500s-1400s, this area is the main area for the generation of N2O. x and N2O emission suppression control methods, such as Figure 3 As shown by the red curve in the middle, the amount of N2O generated in the main area is high, but when the NO x When the N2O emission suppression control method is used, as shown by the blue curve, the N2O emission can be effectively suppressed to a lower level.

[0034] 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 NOx based on ammonia storage synergy x and a N2O emission suppression control method, characterized in that, The ammonia storage capacity of each SCR stage is dynamically adjusted according to the exhaust temperature and conversion efficiency of the two-stage SCR, specifically: Obtain the conversion efficiency of the front-stage SCR and the exhaust temperature of the rear-stage SCR; When the conversion efficiency of the front-stage SCR is greater than or equal to a set first conversion threshold, and the exhaust temperature of the rear-stage SCR is greater than or equal to a set first temperature threshold, a dynamic negative correction is made to the ammonia storage amount of the front-stage SCR to reduce the ammonia storage amount of the front-stage SCR, and a dynamic positive correction is made to the ammonia storage amount of the rear-stage SCR to increase the ammonia storage amount of the rear-stage SCR; When the conversion efficiency of the front-stage SCR is greater than or equal to a set second conversion threshold, and the exhaust temperature of the rear-stage SCR is greater than or equal to a set second temperature threshold, a dynamic negative correction is performed on the ammonia storage amount of the front-stage SCR to reduce the ammonia storage amount of the front-stage SCR, and the ammonia storage amount of the rear-stage SCR is maintained at the current ammonia storage amount; The dynamic negative correction is specifically: obtaining a front-stage real-time ammonia storage value of the front-stage SCR, comparing the front-stage real-time ammonia storage value with a set target ammonia storage value of the front-stage SCR to obtain a front-stage ammonia storage deviation value; obtaining a front-stage predicted ammonia storage value of the front-stage SCR through an ammonia storage closed-loop calculation formula, and using the difference between the front-stage predicted ammonia storage value and the front-stage ammonia storage deviation value as the front-stage dynamic ammonia storage value after dynamic negative correction of the ammonia storage amount of the front-stage SCR; The dynamic positive correction is specifically: obtaining a rear-stage real-time ammonia storage value of the rear-stage SCR, comparing the rear-stage real-time ammonia storage value with a set target ammonia storage value of the rear-stage SCR to obtain a rear-stage ammonia storage deviation value; obtaining a rear-stage predicted ammonia storage value of the rear-stage SCR using an ammonia storage closed-loop calculation formula, and using the sum of the rear-stage predicted ammonia storage value and the rear-stage ammonia storage deviation value as the rear-stage dynamic ammonia storage value after dynamically positively correcting the ammonia storage amount of the rear-stage SCR; The ammonia storage closed-loop calculation formula is: Where n = 1 means that the closed-loop calculation formula for ammonia storage calculates the predicted ammonia storage value of the front stage, and n = 2 means that the closed-loop calculation formula for ammonia storage calculates the predicted ammonia storage value of the back stage; u(t n ) is the predicted ammonia storage value; Kp n is the proportional coefficient of urea injection amount based on ammonia storage deviation control; e(t) is the temperature deviation; dt n Ti is the urea injection amount integration time; n Td is the integral control time of urea injection amount; n is the differential control time of urea injection amount; de(t n ) is the differential time of urea injection amount; t is the regeneration temperature correction time; T is the differential correction time of urea injection amount deviation; An equivalent amount of urea is injected to the front end of each SCR stage according to the ammonia storage amount.

2. A NO based on ammonia storage synergy according to claim 1 x and a N2O emission suppression control method, characterized in that, When the exhaust temperature of the rear-stage SCR is lower than a set first temperature threshold, the ammonia storage amount of the front-stage SCR is the target ammonia storage value, and the ammonia storage amount of the rear-stage SCR is maintained at the current ammonia storage amount.

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