A Catalytic Performance Evaluation Method for a Diesel Engine Post-treatment De-NOx System

Abstract

The present invention relates to the technical field of diesel engine after-treatment, and particularly relates to a method for evaluating the catalytic performance of a denitrogenation and deoxidation system for diesel engine after-treatment, comprising the following steps: S1. Obtain n steady-state operating points of the diesel engine; S2. Operate the diesel engine at each steady-state operating point to obtain the conversion efficiency of the catalyst of the denitrogenation and deoxidation system for diesel engine after-treatment and the catalyst response time at each steady-state operating point. The present invention can comprehensively analyze the conversion efficiency and response time of the after-treatment catalyst, better evaluate the catalytic ability of the catalyst under the instantaneous operating conditions of the engine after-treatment system, and provide data support for its design, selection and optimization; moreover, the results of the steady-state point test of the present invention can be considered to have excluded the influence of other factors, and a series of after-treatment emission data can be obtained by adjusting specific engine parameters, which can assist in optimizing the calibration and optimization of engine parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of diesel engine aftertreatment testing, and particularly relates to a method for evaluating the catalytic performance of a diesel engine aftertreatment de-NOx system. Background Art

[0002] With the decreasing upper limit requirement for vehicle nitrogen oxide emissions, the requirements for the catalytic performance of engine aftertreatment are becoming increasingly strict. The engine aftertreatment system mainly consists of a catalytic converter, a urea tank, a urea supply unit, a urea nozzle, a nitrogen oxide sensor, an exhaust gas temperature sensor, a spray line, etc. During the aftertreatment process, the feeding unit sprays a urea amount matching the engine operating conditions into the exhaust pipe. The ammonia decomposed from the urea and the nitrogen oxides undergo a catalytic reduction reaction in the catalytic converter and finally generate harmless nitrogen gas (N2) and water (H2O). The catalyst performance is the key factor affecting the effect of the catalytic reduction reaction. In actual development and design, to ensure that the product can meet the emission requirements throughout its entire life cycle, it is necessary to verify the catalytic conversion performance of the aftertreatment system at various stages such as selection, design, and durability.

[0003] In the prior art, to verify the catalytic conversion performance of a diesel engine aftertreatment system, it is usually selected to conduct emission tests on an engine test bench by running the type inspection item standards or non-standard cycles specified in GB17691-2018. The regulatory cycle emissions can well reflect the overall emission status of the engine aftertreatment assembly, but it is affected by multiple factors such as the engine emission strategy and the performance of the aftertreatment catalyst, and cannot independently evaluate the catalytic conversion effect of the aftertreatment system, thus affecting the further improvement and optimization of the aftertreatment system and its catalyst. Summary of the Invention

[0004] Aiming at the problem that the catalytic performance of the prior art cannot be independently evaluated, the present invention provides a method for evaluating the catalytic performance of a diesel engine aftertreatment de-NOx system, which can independently evaluate the catalytic performance of the diesel engine aftertreatment system and helps to optimize and improve the aftertreatment system.

[0005] The present invention provides a method for evaluating the catalytic performance of a diesel engine aftertreatment de-NOx system, including the following steps:

[0006] S1. Obtain n steady-state operating points of the diesel engine, where n is an integer and n≥1;

[0007] S2. Run the diesel engine at each steady-state operating point to obtain the catalyst conversion efficiency and the catalyst response time of the diesel engine aftertreatment de-NOx system at each steady-state operating point;

[0008] Wherein:

[0009] Catalyst conversion efficiency = 100%×(1 - [NO xd / [NO x u ),[NO x u 、[NO x d are the average values of the nitrogen oxide concentrations before and after post-treatment in the last minute before the diesel engine runs at each steady-state operating point respectively.

[0010] Catalyst response time = t2 - t1, where t1 is the time when the nitrogen oxide concentration in the post-treatment system starts to change at each steady-state operating point of the diesel engine, and t2 is the time when the post-treatment nitrogen oxide concentration drops to 20% of the initial concentration.

[0011] Further, in step S1, the method for obtaining n steady-state operating points of the diesel engine is to analyze the exhaust temperature and exhaust flow rate map of the diesel engine. Within the exhaust temperature range during normal engine operation, select n temperature values at a fixed temperature interval. At each temperature value, select the point with the highest exhaust flow rate value at that temperature as the steady-state operating point.

[0012] Further, in step S2, run the diesel engine from the high-temperature steady-state operating point to the low-temperature steady-state operating point in sequence.

[0013] Further, in step S2, before each steady-state operating point is executed, the urea injection of the diesel engine post-treatment system is stopped, and the ammonia storage is emptied by heating up.

[0014] Further, in step S2, after the emission state of the diesel engine is stable at each steady-state operating point, urea injection is started, and correction is performed when the emission state is unstable.

[0015] Further, the diesel engine emission state stability standard is set as follows: the exhaust temperature change within 1 minute < 0.1 °C, and the exhaust nitrogen oxide concentration change within 1 minute < 1 ppm.

[0016] Further, fix the urea injection amount at each steady-state operating point, and this urea injection amount makes the ammonia-nitrogen ratio of the engine post-treatment denitration oxygen system ≥ 1.

[0017] Further, the exhaust temperature, exhaust flow rate, nitrogen oxide concentration, and urea injection amount of the diesel engine post-treatment system are measured through the engine test bench.

[0018] ​​​​The beneficial effects of the present invention are as follows. Through the Steady State Test (SST), a series of appropriate engine steady-state operating points are selected. By operating the engine test bench at each steady-state operating point, the nitrogen oxide (limit) catalyst conversion efficiency and response time of the engine after-treatment system can be obtained respectively. By comprehensively analyzing the after-treatment catalyst conversion efficiency and response time, the catalytic ability of the catalyst under the transient operating conditions of the engine after-treatment system can be better evaluated, providing data support for its design, selection and optimization. Moreover, the results of the steady-state point test of the present invention can be considered to have excluded the influence of other factors. By adjusting specific engine parameters, a series of after-treatment emission data can be obtained, which can assist in optimizing the engine parameter calibration and optimization. Detailed implementation manners

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] Embodiment 1

[0021] The catalytic performance evaluation method of the post-treatment denitration system for a diesel engine in this embodiment involves setting the parameters of the post-treatment system of the diesel engine as follows: at the rated point, the exhaust gas flow rate of the engine is 2000 kg / h, and the gas flow temperature before the denitration system is 500 °C. By analyzing the exhaust gas temperature and exhaust gas flow rate map of the engine, within the exhaust gas temperature range during normal engine operation, n temperature values are selected at fixed temperature intervals. At each temperature value, the point with the highest exhaust gas flow rate at that temperature value is selected as the steady-state operating point. Specifically, with a temperature interval of 100 °C, the selected temperatures are 500 °C, 400 °C, 300 °C, and 200 °C, and their corresponding highest exhaust gas flow rates are 2000 kg / h, 1600 kg / h, 1200 kg / h, and 800 kg / h respectively. The above exhaust gas temperatures and the highest exhaust gas flow rates are combined, and the corresponding steady-state operating points are found on the engine test bench and marked as operating condition one, operating condition two, operating condition three, and operating condition four respectively, where operating condition one is the rated point condition. The urea injection amount at each operating point is calculated according to an ammonia-nitrogen ratio (ANR) of 1.2. During the test, the engine test bench records data throughout the process, including but not limited to the nitrogen oxide concentrations before and after the post-treatment system, the gas flow temperature before the denitration system, the gas flow rate, the urea injection amount, and time data, etc. Urea is injected after the diesel engine reaches a stable emission state at each steady-state operating point, and corrections are made when the emission state is unstable. The stable standard for the diesel engine emission state is set as follows: the exhaust gas temperature change within 1 minute < 0.1 °C, and the exhaust gas nitrogen oxide concentration change within 1 minute < 1 ppm.

[0022] At the steady-state operating point, the test procedure is executed according to the following steps:

[0023] Step 1: The engine operates under operating condition one without injecting urea. When it reaches a stable state, start recording data. At this time, record the time t0 = 0 s and operate this condition for 30 minutes.

[0024] Step 2: Inject urea according to an ammonia-nitrogen ratio of 1.2 and operate for 30 minutes. During this period, the moment when the nitrogen oxide concentration after the post-processor starts to change is recorded as t 1,500℃ = 1210 s; when it drops to 20% of the original concentration, record t 2,500℃ = 1212 s. Within the last 1 minute, the average value of the nitrogen oxide concentration before the post-processor is recorded as [NO x u，500℃ = 1000 ppm, and the average value of the nitrogen oxide concentration after the post-processor is recorded as [NO x d，500℃ = 100 ppm.

[0025] Step 3: Stop injecting urea and operate under operating condition one for 10 minutes. Under the condition of not injecting urea, adjust the engine to operating condition two and operate for 30 minutes until it reaches a stable state.

[0026] ​​Step 4: Spray urea according to an ammonia-nitrogen ratio of 1.2 and run for 30 minutes. During this period, the moment when the NOx concentration after the post-processor starts to change is recorded as t 1,400℃ = 6010 s; when it drops to 20% of the original concentration, record t 2，400℃ = 6013 s; within the last 1 minute, the average NOx concentration in front of the post-processor is denoted as [NO x u，400℃ = 800 ppm, and the average NOx concentration after the post-processor is denoted as [NO x d，400℃ = 60 ppm.

[0027] Step 5: Stop spraying urea and run under operating condition 1 for 10 minutes. Under the condition of not spraying urea, adjust the engine to operating condition 3 and run for 30 minutes until it reaches a stable state.

[0028] Step 6: Spray urea according to an ammonia-nitrogen ratio of 1.2 and run for 30 minutes. During this period, the moment when the NOx concentration after the post-processor starts to change is recorded as t 1，300℃ = 10210 s; when it drops to 20% of the original concentration, record t 2，300℃ = 10270 s; within the last 1 minute, the average NOx concentration in front of the post-processor is denoted as [NO x u，300℃ = 500 ppm, and the average NOx concentration after the post-processor is denoted as [NO x d，300℃ = 15 ppm.

[0029] Step 7: Stop spraying urea and run under operating condition 1 for 10 minutes. Under the condition of not spraying urea, adjust the engine to operating condition 4 and run for 30 minutes until it reaches a stable state.

[0030] Step 6: Spray urea according to an ammonia-nitrogen ratio of 1.2 and run for 60 minutes. During this period, the moment when the NOx concentration after the post-processor starts to change is recorded as t 1，200℃ = 14410 s; when it drops to 20% of the original concentration, record t 2，300℃ = 16810 s; within the last 1 minute, the average NOx concentration in front of the post-processor is denoted as [NO x u , 300℃ = 200 ppm, and the average NOx concentration after the post-processor is denoted as [NO x d，300℃ = 20 ppm.

[0031] Calculate the catalyst conversion efficiency under each operating condition according to the following formula. Catalyst conversion efficiency (%) = 100% × (1 - [NO x d / [NO x u );​​​​​​​​

[0032] Calculate the catalyst response time under each working condition according to the following formula: catalyst response time (s) = t2 - t1. The specific results are shown in Table 1.

[0033] Table 1 Catalyst conversion efficiency and catalyst response time of the engine after-treatment system under each working condition in Example 1

[0034] Project Operating Condition 1 Operating Condition 2 Operating Condition 3 Operating Condition 4 Catalyst Conversion Efficiency / % 90 92.5 97 90 Catalyst Response Time / s 2 3 60 2400

[0035] By comprehensively analyzing the conversion efficiency and response time of the after-treatment catalyst at each working condition point, the catalytic ability of the catalyst under the instantaneous working condition of the engine after-treatment system can be better evaluated, providing data support for its design, selection, and optimization.

[0036] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention.

Claims

1. A method for evaluating the catalytic performance of a denitration system for post-treatment of a diesel engine, characterized in that, It includes the following steps: S1. Obtain n steady-state operating points of the diesel engine, where n is an integer and n ≥ 1; S2. Operate the diesel engine at each steady-state operating point to obtain the catalyst conversion efficiency and catalyst response time of the post-treatment de-NOx system of the diesel engine at each steady-state operating point; Where: Catalyst conversion efficiency = 100% × (1 - [NO x d / [NO x u ), where [NO x u and [NO x d are the average concentrations of nitrogen oxides before and after post-treatment, respectively, within one minute before the end of the operation of the diesel engine at each steady-state operating point;​​​​ The catalyst response time = t2 - t1, where t1 is the time when the nitrogen oxide concentration in the post-treatment system starts to change when the diesel engine is at each steady-state operating point, and t2 is the time when the post-treatment nitrogen oxide concentration drops to 20% of the initial concentration; In step S1, the method for obtaining n steady-state operating points of the diesel engine is to analyze the exhaust temperature and exhaust flow universal diagram of the diesel engine. Within the exhaust temperature range during normal engine operation, select n temperature values at a fixed temperature interval. Under each temperature value condition, select the point with the highest exhaust flow value at this temperature value as the steady-state operating point; In step S2, before each steady-state operating point is executed, the urea injection of the diesel engine post-treatment system is stopped, and the ammonia storage is emptied by heating up; In step S2, after the diesel engine emission state is stable at each steady-state operating point, urea injection is started, and correction is performed when the emission state is unstable; The diesel engine emission state stability standard is set as: the exhaust temperature change within 1 minute < 0.1 °C, and the exhaust nitrogen oxide concentration change within 1 minute < 1 ppm; Fix the urea injection amount at each steady-state operating point, and this urea injection amount makes the ammonia-nitrogen ratio of the engine post-treatment de-NOx system ≥ 1.

2. The catalytic performance evaluation method of the diesel engine post-treatment de-NOx system according to claim 1, wherein In step S2, the diesel engine is operated in sequence from the high-temperature steady-state operating point to the low-temperature steady-state operating point.

3. The catalytic performance evaluation method of the diesel engine after-treatment denitrogenation and deoxidation system according to claim 1, characterized in that The exhaust temperature, exhaust flow, nitrogen oxide concentration, and urea injection amount of the diesel engine post-treatment system are measured through an engine test bench.