A method for evaluating the rationality of the layout of nitrogen oxide sensors for diesel engine aftertreatment

Abstract

The present invention relates to the technical field of diesel engine aftertreatment, and more specifically, to a method for evaluating the rationality of the placement of a nitrogen oxide (NOx) sensor for diesel engine aftertreatment. The method comprises the following steps: S1: operating the engine under steady-state conditions and conducting a rationality test on the upstream and downstream nitrogen oxide sensors for aftertreatment by controlling the urea injection rate; S2: operating the engine under WHTC standard transient emission cycle conditions, controlling the urea injection rate and employing a post-treatment calibration release procedure to conduct follow-up tests on the upstream and downstream nitrogen oxide sensors for aftertreatment, respectively. The evaluation method of the present invention effectively reduces the test deviation currently caused by test differences between nitrogen oxide sensors and emission equipment. Furthermore, the method can further confirm the extent to which the placement of the downstream nitrogen oxide sensor of the aftertreatment is affected by the mixing uniformity of the aftertreatment mixer, thereby indirectly evaluating the mixing uniformity of the aftertreatment.

Description

Technical Field

[0001] The present invention relates to the technical field of diesel engine aftertreatment, and in particular to a method for evaluating the rationality of the arrangement position of a nitrogen oxide sensor used for diesel engine aftertreatment. Background Art

[0002] With the continuous development of technology, the emissions of diesel engines have evolved rapidly, and the country's requirements for emission-related regulations have become increasingly perfect.

[0003] With the upgrade of emissions, nitrogen oxide sensors are indispensable components in diesel engine aftertreatment. The layout of nitrogen oxide sensors is related to the rationality of the measurement value of nitrogen oxide sensors. National VI emissions are based on closed-loop feedback control of the measurement value of nitrogen oxide sensors. If the layout of the nitrogen oxide sensors used for aftertreatment is unreasonable, the measurement value will be larger or smaller than the actual value. When the measurement value of the nitrogen oxide sensor is too small, it will cause insufficient urea injection, which will lead to vehicle emissions not meeting national regulations. The PEMS (full name Portable Emission Measurement System, Chinese translation is "vehicle-mounted exhaust detection equipment", the main function of which is to test vehicle emissions in real time) test will not meet the standards; when the measurement value of the nitrogen oxide sensor is too large, it will cause overspray of urea, which will increase the risk of urea crystallization in the aftertreatment process.

[0004] The above description demonstrates the crucial importance of proper placement of NOx sensors. Improper placement, resulting in measured values ​​that are either too high or too low compared to actual values, can lead to vehicle emissions failing to meet national regulations or increase the risk of urea crystallization in the aftertreatment system. Therefore, accurately assessing the proper placement of NOx sensors for diesel engine aftertreatment systems has become a prominent design challenge. Summary of the Invention

[0005] In response to the problem that the rationality of the layout position of a nitrogen oxide sensor for diesel engine aftertreatment cannot be evaluated at present, the present invention proposes a method for evaluating the rationality of the layout position of a nitrogen oxide sensor for diesel engine aftertreatment. The method evaluates the rationality of the layout position of the nitrogen oxide sensor for diesel engine aftertreatment by running steady-state and transient operating condition test programs on a test bench, providing data support for optimizing the layout position of the nitrogen oxide sensor, thereby analyzing the problem of unreasonable nitrogen oxide measurement values ​​caused by unreasonable layout position of the nitrogen oxide sensor through experimental means.

[0006] The present invention proposes a method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment, which specifically includes the following steps:

[0007] S1: Run the engine at steady state and perform rationality tests on the upstream and downstream NOx sensors used for post-treatment by controlling the urea injection rate.

[0008] S2: Run the WHTC standard transient emission cycle conditions, control the urea injection amount and adopt the after-treatment calibration release procedure to perform follow-up tests on the upstream NOx sensor and the downstream NOx sensor for after-treatment respectively.

[0009] Preferably, step S1 mainly includes the following steps:

[0010] (1) Run the engine in steady state, stop urea injection, and test the measurement deviation of the upstream NOx sensor for aftertreatment and the reference NOx sensor at different temperature points;

[0011] (2) Run the engine in steady state, control the urea injection amount, and test the measurement deviation of the downstream NOx sensor for aftertreatment and the reference NOx sensor at different temperature points.

[0012] Preferably, before step S1 , the method further includes step S0 : running the engine in a steady-state condition, and checking the rationality of the reference position and the consistency of the measurement data of the nitrogen and oxygen sensor.

[0013] Preferably, step S0 specifically includes: arranging different nitrogen oxide sensors at the reference position at the same time, fixing the engine exhaust flow and stabilizing the temperature before SCR, and after the measurement value of the nitrogen oxide sensor at the reference position is stable, comparing the average measurement values ​​of different nitrogen oxide sensors, and calibrating the rationality of the reference position and the measurement consistency of the nitrogen oxide sensor.

[0014] Preferably, step S2 mainly includes the following steps:

[0015] (1) Run the WHTC standard transient emission cycle, stop urea injection, and test the followability of the upstream nitrogen oxide sensor for aftertreatment and the reference nitrogen oxide sensor;

[0016] (2) Run the WHTC standard transient emission cycle, urea injection, and adopt the after-treatment calibration release procedure to test the followability of the downstream nitrogen oxide sensor for after-treatment and the reference nitrogen oxide sensor.

[0017] Preferably, urea injection needs to be stopped when the upstream nitrogen oxide sensor for post-processing is performing layout rationality evaluation; urea injection is performed when the downstream nitrogen oxide sensor for post-processing is performing layout rationality evaluation.

[0018] Preferably, when evaluating the rationality of the arrangement position of the downstream nitrogen oxide sensor for post-treatment, the urea injection amount of the engine under steady-state operating conditions is determined based on the actual operating conditions of the vehicle and the catalytic characteristics of the SCR catalyst.

[0019] Preferably, when calculating the deviation between the downstream nitrogen oxide sensor and the reference nitrogen oxide sensor measured by the post-processor in the steady-state engine operating condition, the engine operating condition and the nitrogen oxide concentration must be stable.

[0020] Preferably, the reference nitrogen oxide sensor is installed on the rear exhaust straight pipe of the exhaust outlet of the post-processor, and a mixer is provided in front of the installation position of the reference nitrogen oxide sensor.

[0021] Preferably, the engine steady-state operating condition is a combination of exhaust temperature and exhaust flow selected based on the engine exhaust temperature and exhaust flow in combination with the actual operating condition of the vehicle.

[0022] The beneficial effects of the present invention are:

[0023] The method for evaluating the placement rationality of a nitrogen oxide (NOx) sensor for a diesel engine aftertreatment system, provided by this invention, can be considered to eliminate the influence of other factors. By using a NOx sensor to evaluate the rationality of the aftertreatment NOx sensor's placement, it effectively reduces the testing bias currently caused by differences between NOx sensors and emissions equipment. Furthermore, this method can further confirm the extent to which the placement of the NOx sensor downstream of the aftertreatment system is affected by the mixing uniformity of the aftertreatment mixer, indirectly assessing aftertreatment mixing uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for the description. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the structure of the method for evaluating the rationality of the layout of nitrogen oxide sensors for diesel engine aftertreatment according to the present invention.

[0026] In the figure: 1. Upstream NOx sensor, 2. Reference NOx sensor, 3. Downstream NOx sensor, 4. Mixer. DETAILED DESCRIPTION

[0027] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in this specific embodiment. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of them. Based on the embodiments in this patent, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this patent.

[0028] like Figure 1 As shown, in this embodiment, the present invention proposes a method for evaluating the rationality of the layout position of a nitrogen oxide sensor for diesel engine aftertreatment, which specifically includes the following steps:

[0029] S0: Run the engine under steady-state conditions to verify the appropriateness of the reference position and the consistency of the NOx sensor measurement data. Specifically, different NOx sensors are placed simultaneously at the reference position, with the engine exhaust flow rate and pre-SCR temperature stabilized. After the NOx sensor measurements at the reference position stabilize, the average measurement values ​​of the different NOx sensors are compared to verify the appropriateness of the reference position and the consistency of the NOx sensor measurements. The steady-state engine condition is a combination of exhaust temperature and flow selected based on the engine exhaust temperature and flow rate, combined with the vehicle's actual operating conditions.

[0030] S1: Run the engine in steady-state mode and perform a rationality test on the upstream NOx sensor 1 and the downstream NOx sensor 3 for post-treatment by controlling the urea injection rate;

[0031] S2: Run the WHTC standard transient emissions cycle, control the urea injection rate, and use the aftertreatment calibration release procedure to conduct follow-up tests on the upstream NOx sensor 1 and downstream NOx sensor 3 used for aftertreatment. WHTC refers to the emission limits and measurement methods for urban diesel engines.

[0032] Wherein, step S1 mainly includes the following steps:

[0033] (1) Run the engine in steady state, stop urea injection, and test the measurement deviation of the upstream nitrogen oxide sensor 1 and the reference nitrogen oxide sensor 2 at different temperature points;

[0034] (2) Run the engine in steady state, control the urea injection amount, and test the measurement deviations of the downstream nitrogen oxide sensor 3 for aftertreatment and the reference nitrogen oxide sensor 2 at different temperature points.

[0035] Step S2 mainly includes the following steps:

[0036] (1) Run the WHTC standard transient emission cycle, stop urea injection, and test the followability of the upstream nitrogen oxide sensor 1 for aftertreatment and the reference nitrogen oxide sensor 2;

[0037] (2) Run the WHTC standard transient emission cycle, urea injection, and adopt the after-treatment calibration release procedure to test the followability of the downstream nitrogen oxide sensor 3 for after-treatment and the reference nitrogen oxide sensor 2.

[0038] Specifically, urea injection is stopped when evaluating the placement rationality of the upstream after-treatment NOx sensor 1; urea injection is performed when evaluating the placement rationality of the downstream after-treatment NOx sensor 3. Furthermore, when evaluating the placement rationality of the downstream after-treatment NOx sensor 3, the urea injection amount during steady-state engine operation is determined based on the vehicle's actual operating conditions and the catalytic characteristics of the SCR (selective catalytic reduction) catalyst.

[0039] When calculating the deviation between the downstream NOx sensor 3 and the reference NOx sensor 2 measured by the postprocessor during the steady-state engine operation, it is necessary to ensure that the engine operating condition is stable and the NOx concentration is stable.

[0040] like Figure 1 As shown, the reference NOx sensor 2 is mounted on the exhaust straight pipe at the post-processor exhaust outlet. A mixer 4 is positioned in front of the reference NOx sensor 2 to improve the uniformity of the NOx concentration distribution at the reference location. The rationality of the reference location can also be confirmed by installing multiple NOx sensors at that location and comparing their measurement data.

[0041] The working principle of the rationality evaluation method for the layout of nitrogen oxide sensors for diesel engine aftertreatment is as follows:

[0042] This method evaluates the rationality of the placement of a diesel engine's aftertreatment NOx sensor by running steady-state and transient engine operating tests on a test bench. This test method places certain demands on the test bench. The test bench must be able to control, measure, and record the engine and aftertreatment system's airflow temperature, flow rate, and urea injection rate in real time, as well as the aftertreatment system's NOx concentration.

[0043] It can be seen from the above embodiments that the beneficial effects of the present invention are:

[0044] The method for evaluating the placement rationality of a nitrogen oxide (NOx) sensor for a diesel engine aftertreatment system, provided by this invention, can be considered to eliminate the influence of other factors. By using a NOx sensor to evaluate the rationality of the aftertreatment NOx sensor's placement, it effectively reduces the testing bias currently caused by differences between NOx sensors and emissions equipment. Furthermore, this method can further confirm the extent to which the placement of the NOx sensor downstream of the aftertreatment system is affected by the mixing uniformity of the aftertreatment mixer, indirectly assessing aftertreatment mixing uniformity.

[0045] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment, characterized in that: The specific steps include: S1: Run the engine at steady state and perform rationality testing of the upstream and downstream NOx sensors for post-treatment by controlling the urea injection rate, including: (1) Run the engine in steady state, stop urea injection, and test the measurement deviation of the upstream NOx sensor for aftertreatment and the reference NOx sensor at different temperature points; (2) Run the engine at steady state, control the urea injection rate, and test the measurement deviation of the downstream NOx sensor for aftertreatment and the reference NOx sensor at different temperature points; S2: Run the WHTC standard transient emission cycle, control the urea injection rate and use the after-treatment calibration release procedure to perform follow-up tests on the upstream NOx sensor and the downstream NOx sensor for after-treatment, including: (1) Run the WHTC standard transient emission cycle, stop urea injection, and test the followability of the upstream nitrogen oxide sensor for aftertreatment and the reference nitrogen oxide sensor; (2) Run the WHTC standard transient emission cycle, urea injection, and adopt the after-treatment calibration release procedure to test the followability of the downstream nitrogen oxide sensor for after-treatment and the reference nitrogen oxide sensor.

2. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 1, characterized in that: Before step S1 , the method further includes step S0 : running the engine in a steady-state condition, and checking the rationality of the reference position and the consistency of the nitrogen and oxygen sensor measurement data.

3. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 2, characterized in that: Step S0 specifically includes: placing different nitrogen oxide sensors at the reference position at the same time, fixing the engine exhaust flow and stabilizing the temperature before SCR, and after the nitrogen oxide sensor measurement value at the reference position stabilizes, comparing the average measurement values ​​of different nitrogen oxide sensors, and calibrating the rationality of the reference position and the measurement consistency of the nitrogen oxide sensor.

4. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 1, characterized in that: When the upstream nitrogen oxide sensor for after-treatment is used to evaluate the rationality of its layout, urea injection needs to be stopped; when the downstream nitrogen oxide sensor for after-treatment is used to evaluate the rationality of its layout, urea injection can be carried out.

5. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 4, characterized in that: When evaluating the rationality of the arrangement position of the downstream nitrogen oxide sensor for post-treatment, the urea injection amount under the steady-state engine operating condition is determined based on the actual operating conditions of the vehicle and the catalytic characteristics of the SCR catalyst.

6. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 1, characterized in that: When calculating the deviation between the downstream nitrogen oxide sensor and the reference nitrogen oxide sensor measured by the post-processor during the steady-state operation of the engine, it is necessary to ensure that the engine operating condition and the nitrogen oxide concentration are stable.

7. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 1, characterized in that: The reference nitrogen oxide sensor is installed on the rear exhaust straight pipe of the exhaust outlet of the post-processor, and a mixer is provided in front of the installation position of the reference nitrogen oxide sensor.

8. The method for evaluating the rationality of the layout of a nitrogen oxide sensor for diesel engine aftertreatment according to claim 1, characterized in that: The engine steady-state operating condition is a combination of exhaust temperature and exhaust flow selected based on the engine exhaust temperature and exhaust flow in combination with the actual operating condition of the vehicle.

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