A method for calculating the conversion efficiency of a diesel engine SCR

Abstract

A method for calculating the SCR conversion efficiency of a diesel engine, belonging to the field of diesel engine exhaust aftertreatment, is presented. This method differs from traditional methods based on NO at the SCR inlet and outlet. x The concentration is not calculated by the method described above, but rather based on the SCR outlet O2 concentration and the outlet NO concentration. x The correlation between concentrations and the relationship between SCR conversion efficiency were used to calculate SCR conversion efficiency, and subsequent diagnosis of SCR status was performed to solve the problem of imported NO inlet SCR. x Fluctuations in concentration can easily lead to false alarms, and the installation of the SCR inlet sensor increases the unreliability of the data. This method, by changing the SCR conversion efficiency of the diesel engine in a fixed cycle mode, pre-determines the different conversion efficiencies and SCR outlet NO under that cycle mode. x The correlation between the correlation coefficient and the outlet O2 concentration was established, and then the SCR outlet NO was obtained by entering this cyclic mode. x The correlation coefficient with the outlet O2 concentration is used to obtain the corresponding SCR conversion efficiency.

Description

Technical Field

[0001] This invention relates to the technical field of diesel engine exhaust aftertreatment, and in particular to a method for calculating the SCR conversion efficiency of a diesel engine. Background Technology

[0002] Selective catalytic oxidation (SCR) systems utilize the urea decomposition to produce NH3, which then reacts with NO under the action of a catalyst. x The reaction proceeds, thereby reducing NO. x Emissions. Compared to other after-treatment technologies, it has many advantages such as better fuel economy, higher safety factor, and lower sulfur sensitivity, making it the mainstream diesel engine after-treatment technology both domestically and internationally. SCR technology can effectively control NOx emissions. x Emission levels, and the deterioration or accidental damage of the SCR itself, will affect NO. x The conversion efficiency is greatly affected. To effectively reduce NO in exhaust gases... x It is necessary to ensure the conversion efficiency of the SCR catalyst.

[0003] In practical applications, in order to maintain the conversion of NO by the SCR system x The capability requires real-time monitoring of the conversion efficiency of the SCR system. When the conversion efficiency falls below a certain limit, the customer should be prompted to repair or replace the system.

[0004] The current method for calculating SCR conversion efficiency is as follows:

[0005]

[0006] Where m(NO) x ) in Imported NO for SCR x Mass flow rate, m(NO x ) out NO for SCR exports x Mass flow rate.

[0007] As can be seen from the above formula, the SCR conversion efficiency is affected by the imported NO in the SCR system. x Concentration has a significant impact; SCR imported NO x Fluctuations in NO concentration can easily cause false alarms. Therefore, it is necessary to address the issue of imported NO... x The problem of false alarms caused by concentration fluctuations.

[0008] In addition, installing sensors at the SCR inlet increases installation costs. Furthermore, since sensor measurement data has errors, these errors accumulate over time, increasing the unreliability of the data. Summary of the Invention

[0009] In summary, this application provides a method for judging SCR conversion efficiency, which solves the following two problems:

[0010] 1. SCR imported NO x Fluctuations in concentration can easily cause false alarms.

[0011] 2. The installation of imported SCR sensors increases the problem of data unreliability.

[0012] The technical solution of this invention is implemented as follows: a method for calculating the SCR conversion efficiency of a diesel engine, comprising the following steps:

[0013] S1. Conduct calibration experiments. In a fixed-cycle mode, the SCR conversion efficiency of the diesel engine is changed by altering the amount of injected NH3. The NO at the SCR outlet is measured at different conversion efficiencies. x The curves of the change of outlet O2 concentration over time were obtained and their correlation coefficients were calculated to obtain the relationship between the correlation coefficients and SCR conversion efficiency under this fixed cycle mode.

[0014] S2. Online efficiency calculation. The diesel engine enters this fixed cycle mode, and the NO at the SCR outlet is measured during this cycle. x The correlation coefficient between the outlet O2 concentration and the actual SCR conversion efficiency is obtained based on the relationship between the correlation coefficient and the SCR conversion efficiency.

[0015] S3. SCR Operating Status Diagnosis. Based on the SCR conversion efficiency obtained in step S2, diagnose the operating status of the SCR.

[0016] The principle upon which this invention is based is:

[0017] like Figure 1 As shown, diesel engines emit NO after combustion. x O2 enters SCR, NO x It is excreted after reacting in the SCR. For example... Figure 2 As shown, during the combustion of fuel in a diesel engine cylinder, NO is present in the exhaust gas produced by combustion. x It is correlated with O2. NO is generated during fuel combustion. x The concentration of O2 in the cylinder is related to the engine's performance. Diesel engines generally operate under oxygen-rich conditions, and the NO generated under these conditions... x As the concentration of O2 increases, the concentration of O2 remaining in the cylinder decreases.

[0018] The gases exhausted from the engine will undergo the following reaction when passed through an SCR system:

[0019] SCR reduces NO by NH3 x There are three main reaction mechanisms

[0020] Rapid reaction: 4NH3 + 2NO + 2NO2 → 4N2 + 6H2O

[0021] Standard reaction: 4NO + 4NH3 + O2 → 4N2 + 6H2O

[0022] Slow reaction: 8NH33 + 6NO2 → 7N2 + 12H2O

[0023] As shown in the reaction mechanism above, NO x It is reduced in SCR, compared to imported NO in SCR. x There is a correlation between SCR and imported O2, and exported NO x The correlation with exported O2 was disrupted, such as Figure 2 As shown, this correlation is related to SCR conversion efficiency.

[0024] In this invention, NO x The correlation between NO and O2 is characterized by the correlation coefficient. x The formula for calculating the correlation coefficient between O2 and O2 is as follows:

[0025]

[0026] In the formula, x i y i NO was collected respectively x Raw data on concentration and O2 concentration. NO was collected respectively x The average concentration of O2.

[0027] Based on the above principles, it can be applied based on NO x Conversion rate and SCR export NO x The correlation between the correlation coefficient and the output O2 was established through calibration experiments, showing the relationship between the correlation coefficient and the SCR conversion efficiency of the diesel engine in a fixed cycle mode. Then, based on the correlation coefficient obtained during testing in the fixed cycle mode, the SCR conversion efficiency was calculated.

[0028] As a preferred technical solution, the correlation coefficient and the SCR conversion efficiency are obtained by pre-calibrating and summarizing experimental data or curves.

[0029] As a preferred technical solution, the correlation coefficient and the SCR conversion efficiency correspond one-to-one with the engine model and its SCR system.

[0030] The above-mentioned method for calculating the SCR conversion efficiency of a diesel engine is based on the fact that NO is emitted after diesel engine combustion. xThere is a correlation between O2 and the reaction in the SCR, and this correlation is affected by the reaction in the SCR. This method only requires installing a NO3-52 filter at the SCR outlet. x The sensor can effectively avoid the problem of NO in the SCR inlet. x This reduces false alarms caused by concentration fluctuations and also addresses the issue of data unreliability. Attached Figure Description

[0031] Figure 1 Diagram illustrating the acquisition of detection data.

[0032] Figure 2 SCR import and export NO x Graph showing the changes in concentration and outlet O2 concentration over time.

[0033] Figure 3 SCR conversion efficiency assessment flowchart.

[0034] Figure 4 Case study on SCR conversion efficiency fault diagnosis process. Detailed implementation method:

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Based on the method for calculating the SCR conversion efficiency of a diesel engine proposed in this invention, fault diagnosis of the SCR operating status was performed. The specific diagnostic process is as follows: Figure 4 :

[0037] S1. Conduct calibration experiments. With the diesel engine in a fixed cycle mode, the SCR conversion efficiency is altered by changing the amount of injected NH3. The NO at the SCR outlet is measured at different conversion efficiencies. x The curves of the change of outlet O2 concentration over time were obtained and their correlation coefficients were calculated to obtain the relationship between the correlation coefficients and SCR conversion efficiency under this fixed cycle mode.

[0038] S2. Online efficiency calculation. The diesel engine enters this fixed cycle mode, and the NO at the SCR outlet is measured during this cycle. x The correlation coefficient between the outlet O2 concentration and the actual SCR conversion efficiency is obtained by comparing the correlation coefficient with the SCR conversion efficiency.

[0039] S3. SCR Working Status Judgment. Based on the SCR conversion efficiency obtained in step S2, determine whether the SCR conversion efficiency is less than a preset conversion efficiency threshold. If it is less than the threshold, an SCR fault alarm is triggered.

[0040] It is understandable that in some embodiments, in step S1, the diesel engine enters the fixed cycle mode, which is selected to detect that the vehicle is in neutral and idling, maintain a fixed speed for 15-20 minutes, then accelerate rapidly to the maximum speed, maintain the maximum speed for 10 seconds, and then return to idle; for example... Figure 1 SCR unit diagram, measuring SCR outlet NO using an SCR outlet nitrogen and oxygen sensor. x Concentration and outlet O2 concentration, plot NO x Concentration change curves over time, O2 concentration change curves over time, and NO concentration change curves over time. x Correlation analysis was performed between concentration and O2 concentration to obtain the correlation coefficient;

[0041] Understandably, this fixed cycle mode is not limited to the cycle modes in these instances; other modes can be selected, as long as the selection must include variable operating conditions, which can be achieved by changing the speed, changing the torque, or both.

[0042] In some embodiments, the formula for calculating the correlation coefficient in steps S1 and S2 is as follows:

[0043]

[0044] In the formula, x i y i NO was collected respectively x Raw data on concentration and O2 concentration. This is the average value.

[0045] Specifically, in one instance, a total of M data points were collected. These M data points can be divided into m segments, and the correlation coefficients of the m segments can be calculated for each segment.

[0046]

[0047]

[0048] The correlation coefficient change curve can be obtained, and the correlation coefficient change curve of the detection experiment can be compared with the correlation coefficient change curve of the calibration experiment to obtain the SCR conversion efficiency.

[0049] In some embodiments, when the correlation coefficient is greater than 0.7, the SCR conversion efficiency is less than 40%, the SCR is basically in a non-working state, and the SCR issues a fault alarm.

[0050] The innovation of this invention lies in the fact that this method differs from traditional methods in both its underlying principles and specific application. Traditional methods require knowledge of the SCR inlet and outlet NO. x The concentration is used to calculate the SCR conversion efficiency, while this method will change the SCR outlet NO based on the SCR conversion efficiency.x The principle of correlation between concentration and outlet O2 concentration is used to calculate SCR conversion efficiency. The usage of this invention also differs from traditional methods; this method only requires measuring the SCR outlet NO concentration using the outlet sensor. x The O2 concentration at the outlet is reduced, making it easier to use.

[0051] The beneficial effects of this invention are: by utilizing the SCR outlet NO x The correlation between the O2 concentration at the outlet and the SCR conversion efficiency allows for the calculation of the SCR conversion efficiency. This process only requires installing a NO₂ outlet at the SCR outlet. x The sensor saves costs while improving the reliability of SCR conversion efficiency calculation, ensuring the detection of NO. x The effectiveness of conversion efficiency allows for a more accurate assessment of the SCR's operating status. This method is applicable to rapid detection on actual roads and is a form of in-service evaluation.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the present invention, and these will not affect the effectiveness and practicality of the present invention.

Claims

1. A method of calculating the conversion efficiency of a diesel engine SCR, characterized in that The method comprises the following steps: S1, conducting calibration experiments; The diesel engine was in the fixed cycle mode, the conversion efficiency of SCR was changed by changing the injection amount of NH3, the NOx concentration at the outlet of SCR under different conversion efficiencies was measured x The corresponding relationship between the correlation coefficient and the conversion efficiency of SCR was obtained by measuring the change curve of the NOx concentration at the outlet of SCR and the O2 concentration at the outlet of SCR over time and calculating the correlation coefficient. S2, calculating efficiency on line; The diesel engine enters the fixed cycle mode, and the SCR outlet NO x and the outlet O2 concentration, calculates a correlation coefficient, obtains the actual SCR conversion efficiency according to a corresponding relationship between the correlation coefficient and the SCR conversion efficiency in the calibration experiment; S3, diagnosing the working state of the SCR; The working state of the SCR is diagnosed according to the SCR conversion efficiency obtained in step S2.

2. A method of calculating the conversion efficiency of a diesel engine SCR as recited in claim 1, characterized in that: The corresponding relationship between the correlation coefficient and the SCR conversion efficiency is pre-calibrated and summarized as data or a curve through experimental data.

3. The method of claim 1, wherein the method of calculating the correlation coefficient is characterized in that the correlation coefficient represents a correlation between the concentrations of O2 and NO x and is calculated according to the following equation: In the formula, x i , y i are the raw data of the collected NO x concentration and O2 concentration, respectively, are the average values of the collected NO x concentration and O2 concentration, respectively.

4. The method according to claim 1, wherein the fixed cycle mode must include a variable working condition, which is a change in rotation speed or a change in torque or both.

5. A method of calculating the conversion efficiency of a diesel engine SCR according to claim 1, wherein the test data is obtained by measuring only the NOx concentration at the outlet of the SCR and the O2 concentration at the outlet of the SCR. x x concentration at the outlet of the SCR and the O2 concentration at the outlet of the SCR.​

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