Self-repairing national 7 diesel engine post-processing system and control method
By replacing SCR with MFC in the diesel engine after-treatment system and decomposing impurities through real-time monitoring and temperature control, the problem of SCR poisoning is solved, and efficient NOx emission reduction and temperature conversion are achieved to meet the National VII emission standards.
Patent Information
- Application Number
- CN202510887846.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-30
- Publication Date
- 2025-09-19
AI Technical Summary
When existing diesel engine after-treatment systems meet the European National VII emission standards, there are problems such as adding DOC to decompose impurities, resulting in high costs, limited space and increased fuel consumption. In addition, the SCR is easily poisoned, resulting in reduced conversion efficiency.
A multifunctional catalyst MFC is used to replace SCR. By real-time monitoring of NOx emissions and temperature, the poisoning status is determined. When poisoning occurs, the temperature is controlled by controlling the amount of fuel injected remotely to decompose impurities. Urea injection is combined to reduce NOx emissions and increase temperature.
It achieves the efficient decomposition of SCR surface impurities, restores MFC performance, meets the National VII emission standards, reduces NOx emissions and improves temperature conversion efficiency without increasing costs and space restrictions.
Smart Images
Figure CN120667235A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to post-processing, and more particularly, to a self-repairing National VII diesel engine post-processing system and a control method. Background Art
[0002] Europe has released the next stage of vehicle emission standards, Euro VII regulations. Compared with the current Euro VI standards, this regulation has put forward higher requirements for emission pollutants such as NOx, PM, PN, and NH3. NOx is one of the main emission pollutants of diesel engines. The emission limit of National VI is already very low, and it will be even lower under the National VII regulations. At present, the industry has reached a general consensus that the NOx emissions of diesel engines must meet the requirements of the future National VII regulations, and a two-stage urea injection after-treatment system is required. The structure of the after-treatment system is as follows: Figure 1 shown.
[0003] The application of a two-stage urea injection post-treatment system can achieve extremely low NOx emissions. During the actual use of the vehicle, impurities such as hydrocarbons, sulfates, etc. are generated. The first-stage SCR is in direct contact with the exhaust gas emitted by the engine. After long-term operation, a large amount of impurities accumulate on the surface of the SCR, which will damage the molecular sieve, resulting in a decrease in the SCR poisoning conversion efficiency. Impurities such as hydrocarbons, sulfates, etc. can be decomposed at high temperatures. The current common practice is to add a diesel oxidation catalyst (DOC) in front of the first-stage SCR. When there are too many impurities, the engine will release them far after injection. The diesel will oxidize in the DOC and release heat to increase the temperature and decompose the impurities in the SCR at high temperatures. However, adding a DOC will increase costs and will be constrained by the installation space of the entire vehicle. It will also increase exhaust resistance and affect the fuel consumption and power of the engine. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a self-repairing National VII diesel engine after-treatment system and control method, which can not only catalyze the chemical reaction of NOx and NH3 to reduce NOx emissions, but also catalyze the chemical reaction of HC and O2 to increase the temperature.
[0005] The present invention provides a method for controlling a self-repairing National VII diesel engine after-treatment system, the method comprising the following steps:
[0006] S1: An MFC is set in the first-stage urea injection unit of the post-treatment system, and the front NOx emission Q1 and the rear NOx emission Q2 on both sides of the MFC are collected, as well as the inlet temperature T1 and the inlet temperature T2 on both sides of the MFC;
[0007] S2: Calculate the NOx conversion efficiency η1 based on the front NOx emission Q1 and the rear NOx emission Q2, and calculate the MFC temperature based on the inlet temperature T1 and the inlet temperature T2;
[0008] S3: Setting the efficiency limit η2, judging whether the MFC is poisoned according to the NOx conversion efficiency η1 and the efficiency limit η2, if the MFC is not poisoned, executing the original control strategy; if the MFC is poisoned, entering the impurity cleaning mode.
[0009] Preferably, the impurity cleaning mode is: after the diesel is completely burned in the cylinder, the remote after-spray is released to thermally decompose the sprayed diesel into HC, and the HC is discharged into the MFC along with the exhaust gas.
[0010] Preferably, the remote post injection amount of the remote post injection is determined by the following method: obtaining the engine speed and torque, calibrating the remote post injection amount according to the engine speed and torque, then comparing the MFC temperature with a set high temperature target value, and correcting the remote post injection amount according to the comparison result so that the actual temperature of the MFC after correction is the high temperature target value.
[0011] Preferably, when the temperature of the MFC reaches the high temperature target value and the accumulated time reaches the set time, a mark indicating that the impurities have been cleaned is issued, and the original control strategy is restored, and the release of the remote spray is stopped.
[0012] Preferably, in S3, if η1≥η2, it is determined that the MFC is not poisoned; if η1<η2, it is determined that the MFC is poisoned.
[0013] Preferably, the calculation formula of the NOx conversion efficiency η1 is:
[0014] η1=1-Q2 / Q1.
[0015] Preferably, the calculation formula of the MFC temperature is:
[0016] T MFC =a*T1+(1-a)*T2,
[0017] Where, T MFC is the MFC temperature; a is the temperature coefficient set according to the MFC characteristics.
[0018] Preferably, the original control strategy is to inject urea into the MFC so as to catalyze a chemical reaction between NOx and NH3 through the MFC.
[0019] A self-repairing National VII diesel engine after-treatment system for realizing the control method of the self-repairing National VII diesel engine after-treatment system comprises a first-stage urea injection unit and a second-stage urea injection unit arranged in the exhaust duct; the first-stage urea injection unit is provided with an MFC, and the second-stage urea injection unit is provided with a DOC, a DPF, an SCR, and an ASC in sequence along the exhaust direction.
[0020] Beneficial effects
[0021] The advantages of the present invention are:
[0022] 1. The present invention uses a multifunctional catalyst MFC to replace the SCR of the current technology route, which can not only catalyze the chemical reaction of NOx and NH3 to reduce NOx emissions, but also catalyze the chemical reaction of HC and O2 to increase the temperature.
[0023] 2. A new impurity cleaning mode is added based on the NOx conversion efficiency before and after the MFC to achieve high-temperature decomposition of impurities accumulated on the MFC surface.
[0024] 3. The post-injection amount is roughly adjusted based on engine speed and torque output, and finely adjusted based on the difference between the measured MFC temperature and the target temperature, accurately controlling the temperature and efficiently restoring MFC performance. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a schematic diagram of the structure of a traditional two-stage urea injection post-treatment system;
[0026] Figure 2 This is a structural diagram of the self-repairing National VII diesel engine after-treatment system of the present invention;
[0027] Figure 3 This is a flow chart of the control method of the post-processing system of the present invention. DETAILED DESCRIPTION
[0028] 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.
[0029] Example 1
[0030] See Figure 2-Figure 3 The present invention provides a control method for a self-repairing National VII diesel engine after-treatment system, the method comprising the following steps:
[0031] S1: An MFC (Multi Functional Catalyst) is installed in the first-stage urea injection unit. NOx sensors placed before and after the MFC measure front NOx emissions Q1 and rear NOx emissions Q2 in real time. Temperature sensors placed before and after the MFC measure real-time inlet temperatures T1 and T2.
[0032] S2: Calculate the NOx conversion efficiency η1 based on the front NOx emission Q1 and the rear NOx emission Q2. The calculation formula is: η1 = 1-Q2 / Q1. Calculate the MFC temperature based on the inlet temperature T1 and the inlet temperature T2. The calculation formula is T MFC=a*T1+(1-a)*T2, where a is the temperature coefficient set according to the MFC characteristics.
[0033] S3: Based on the MFC temperature, the efficiency model interpolates the efficiency limit η2 for the current operating conditions. The MFC is then determined to be poisoned based on the NOx conversion efficiency η1 and the efficiency limit η2. If η1 ≥ η2, the NOx conversion efficiency is normal and the MFC is not poisoned. The engine operates according to the original control strategy, injecting urea into the MFC. The MFC catalyzes the chemical reaction between NOx and NH3, reducing NOx emissions. If η1 < η2, the NOx conversion efficiency is very low, and the temperature needs to be increased to decompose and remove impurities such as HC and sulfate from the MFC surface. The engine then enters impurity cleaning mode.
[0034] S4: When entering the impurity cleaning mode, the engine completes combustion in the cylinder and then releases the remote spray. The sprayed diesel is thermally decomposed into HC and discharged into the MFC along with the exhaust gas. The MFC catalyzes the chemical reaction between HC and O2 to release heat and increase the temperature.
[0035] S5: The remote post-injection fuel quantity is initially calibrated based on the current engine speed and torque. The remote post-injection fuel quantity is then adjusted based on the current measured MFC temperature and the high-temperature target value set for impurity decomposition. The actual MFC temperature is then precisely controlled to the high-temperature target value. Once the MFC temperature reaches the high-temperature target value for a set period of time, impurity removal is complete, the original control strategy is restored, and remote post-injection is discontinued.
[0036] Example 2
[0037] A self-repairing National VII diesel engine aftertreatment system control method for the aforementioned self-repairing National VII diesel engine aftertreatment system comprises a first-stage urea injection unit and a second-stage urea injection unit disposed in the exhaust duct; the first-stage urea injection unit is equipped with an MFC, while the second-stage urea injection unit is equipped with a DOC, a DPF, an SCR, and an ASC in sequence along the exhaust direction. Specifically, the present invention replaces the traditional SCR in the first-stage urea injection unit with an MFC. The catalytic action of the MFC not only catalyzes the chemical reaction between NOx and NH3 to reduce NOx emissions, but also catalyzes the chemical reaction between HC and O2 to increase the temperature.
[0038] 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 control method for a self-repairing National VII diesel engine after-treatment system, characterized in that: The method comprises the following steps: S1: An MFC is set in the first-stage urea injection unit of the post-treatment system, and the front NOx emission Q1 and the rear NOx emission Q2 on both sides of the MFC are collected, as well as the inlet temperature T1 and the inlet temperature T2 on both sides of the MFC; S2: Calculate the NOx conversion efficiency η1 based on the front NOx emission Q1 and the rear NOx emission Q2, and calculate the MFC temperature based on the inlet temperature T1 and the inlet temperature T2; S3: Setting the efficiency limit η2, judging whether the MFC is poisoned according to the NOx conversion efficiency η1 and the efficiency limit η2, if the MFC is not poisoned, executing the original control strategy; if the MFC is poisoned, entering the impurity cleaning mode.
2. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 1, characterized in that: The impurity cleaning mode is: after the diesel is completely burned in the cylinder, the remote after-spray is released to thermally decompose the sprayed diesel into HC, and the HC is discharged into the MFC along with the exhaust gas.
3. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 2, characterized in that: The remote post-injection fuel quantity of the remote post-injection is determined by the following method: obtaining the engine speed and torque, calibrating the remote post-injection fuel quantity based on the engine speed and torque, then comparing the MFC temperature with a set high-temperature target value, and correcting the remote post-injection fuel quantity based on the comparison result so that the actual temperature of the MFC after correction is the high-temperature target value.
4. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 3, characterized in that: When the temperature of the MFC reaches the high temperature target value and the accumulated time reaches the set time, the impurity cleaning completion flag is issued, and the original control strategy is restored at the same time, and the release of the remote spray is stopped.
5. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 1, characterized in that: In S3 , if η1 ≥ η2, it is determined that the MFC is not poisoned; if η1 < η2, it is determined that the MFC is poisoned.
6. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 1, characterized in that: The calculation formula of the NOx conversion efficiency η1 is: η1=1-Q2 / Q1.
7. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 1, characterized in that: The calculation formula of the MFC temperature is: T MFC =a*T1+(1-a)*T2, Where, T MFC is the MFC temperature; a is the temperature coefficient set according to the MFC characteristics.
8. The control method of a self-repairing National VII diesel engine after-treatment system according to claim 1, characterized in that: The original control strategy is to inject urea into the MFC so as to catalyze the chemical reaction between NOx and NH3 through the MFC.
9. A self-repairing National VII diesel engine after-treatment system for implementing the control method of the self-repairing National VII diesel engine after-treatment system according to any one of claims 1 to 8, characterized in that: It includes a first-stage urea injection unit and a second-stage urea injection unit arranged in the exhaust duct; the first-stage urea injection unit is provided with an MFC, and the second-stage urea injection unit is provided with a DOC, a DPF, an SCR, and an ASC in sequence along the exhaust direction.