Engine DeNO X EGR Valve Coking Test Method in [Operating] Mode

Abstract

The invention discloses a method for the coking test of an EGR valve in the DeNOx mode of an engine, which is characterized by including the following steps: 1) After the engine starts, it runs in the idle condition and the warm engine condition for a time T0. 2) When the engine water temperature reaches normal, it enters the LNT trapping stage, that is, it runs in the Pmax condition for a time T1. 3) After the NOx adsorption settlement, it enters the NOx reduction stage, that is, it runs in the DeNOx condition for a time T2. 4) The engine idles and stops, and stands still until the engine water temperature drops to 40 ± 2 °C. 5) Repeat steps 1) to 4) until the test reaches the termination condition. The invention makes full use of the technical characteristics of the LNT aftertreatment technology, selects the Pmax condition and the DeNOx condition to shorten the test time and save the test cost; increases the standing still time after shutdown to simulate the actual vehicle use, and provides conditions for the coking of the EGR valve. And it provides a verification means for the coking of the EGR valve under the LNT aftertreatment technology, and can effectively evaluate the reliability of the EGR coupling LNT system.

Description

Technical Field

[0001] The present invention relates to an engine test method, specifically to an EGR system engine based on LNT post-treatment technology, and to the verification test of EGR valve coking in the engine DeNOx combustion mode. Background Art

[0002] The lean burn NOx trap technology of the engine is also called LNT, which has a good effect on reducing NOx emissions. Compared with the SCR system, it has the characteristics of simple system and small occupied space, and is suitable for the installation and use of light diesel vehicles. In the control strategy route for engine NOx emissions, the collaborative control technology route of EGR coupling with the LNT system is usually adopted. In the design of the EGR coupling LNT system, most researchers at home and abroad focus on studying the influence of the structure design of the LNT system, the noble metal components and content, the EGR rate, etc. on the NOx conversion efficiency. There are few literatures on the risk assessment of a large amount of hydrocarbons (CxHy) in the engine post-treatment system during the NOx reduction stage in the LNT technology route on the coking of the EGR valve. Summary of the Invention

[0003] The purpose of the present invention is to solve the deficiencies existing in the above background art, and to propose an EGR valve coking test method in the engine DeNOx mode that can simulate real vehicle usage conditions, has a short test time, and low test costs.

[0004] To achieve the above purpose, the present invention provides an EGR valve coking test method in the engine DeNOx mode, which is characterized by including the following steps:

[0005] 1) After the engine starts, it runs in the idle condition and the warm-up condition for a time T0.

[0006] 2) When the engine water temperature reaches normal, it can enter the LNT capture stage, that is, run in the Pmax condition for a time T1.

[0007] 3) After the NOx adsorption settlement, it enters the NOx reduction stage, that is, runs in the DeNOx condition for a time T2.

[0008] 4) The engine idles and stops, and stands still until the engine water temperature drops to 40 ± 2 °C.

[0009] 5) Repeat steps 1) to 4) until the test reaches the abort condition.

[0010] As a preferred embodiment of the present invention, step 2) is as follows: During the LNT capture stage, the adsorbed NOX is temporarily stored on the carrier in the form of Ba(NO3)2. In order to accelerate the adsorption of NOX and shorten the adsorption time, we select the rated power operating point Pmax at which the engine generates the maximum NOX emissions. The adsorption time T1 is determined by the NOX adsorption saturation degree and is determined by the NOX sensor concentration measurement values before and after the LNT post-treatment.

[0011] Furthermore, step 3) is as follows: Utilize the engine DeNOx operating condition. At this time, the LNT is in the reduction stage. There are relatively many HC compounds in the engine exhaust gas, which easily causes the EGR valve to coke, thus creating conditions for the coking of the EGR valve. The operation time T2 of the DeNOx condition in the reduction stage is determined by the NOX conversion efficiency and is determined by the oxygen sensor concentration measurement values before and after the LNT post-treatment. O2 will be precipitated during the LNT reduction stage. When the oxygen concentrations before and after the LNT post-treatment are equal, it indicates that the DeNOx stage is completed.

[0012] Even further, step 4) is as follows: Stop the engine and let it stand still, allowing the hot HC compounds to naturally cool and deposit on the EGR valve; in this way, the alternating of hot and cold simulates the actual usage state of real users and creates favorable conditions for the coking of the EGR valve. The standing still time is determined by the engine water temperature, and the engine water temperature naturally cools to 40 ± 2°C.

[0013] Even further, step 5) is as follows: Repeat steps 1) to 4) until the test is aborted when the feedback value of the EGR valve opening degree, the voltage value of the EGR valve are abnormal, or the engine emissions and performance parameters deteriorate by 5%.

[0014] The present invention makes full use of the technical characteristics of the LNT post-treatment, selects the Pmax condition and the DeNOx condition to shorten the test time and save the test cost; increases the standing still time after shutdown to simulate the actual vehicle use situation and provides conditions for the coking of the EGR valve. And it provides a verification method for the coking of the EGR valve under the LNT post-treatment technology, and can effectively evaluate the reliability of the EGR coupled with the LNT system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the schematic diagram of the present invention.

[0016] Figure 2 is NO X The schematic diagram of the adsorption and capture stage.

[0017] Figure 3 is NO X The schematic diagram of the reduction stage. DETAILED DESCRIPTION OF THE INVENTION

[0018] The technical solutions (including the preferred technical solutions) of the present invention will be further described in detail below by means of the accompanying drawings and by listing some optional embodiments of the present invention.

[0019] As shown in the figure, the present invention discloses a method for testing the coking of an EGR valve in the DeNOx mode of an engine, which includes the following steps:

[0020] 1) After the engine starts, it runs in the idle condition and the warm engine condition for a time T0.

[0021] 2) When the engine water temperature reaches normal, it can enter the LNT capture stage, that is, run in the Pmax condition for a time T1.

[0022] 3) After the NOx adsorption settlement, enter the NOx reduction stage, that is, run in the DeNOx condition for a time T2.

[0023] 4) The engine idles and stops, and waits for the engine water temperature to drop to 40 ± 2 °C.

[0024] 5) Repeat steps 1) to 4) until the test reaches the abort condition.

[0025] Step 2) is as follows: In the LNT capture stage, the adsorbed NOX is temporarily stored on the carrier in the form of Ba(NO3)2. In order to accelerate the NOX adsorption and shorten the adsorption time, we select the rated power condition point Pmax at which the engine generates the maximum NOX emissions. The adsorption time T1 is determined by the NOX adsorption saturation degree, which is determined by the NOX sensor concentration measurement values before and after the LNT post-treatment.

[0026] Step 3) is as follows: Utilize the engine DeNOx operating condition. At this time, the LNT is in the reduction stage, and there are more HC compounds in the engine exhaust gas, which easily causes the EGR valve to coke, thus creating conditions for the coking of the EGR valve. The operation time T2 of the DeNOx condition in the reduction stage is determined by the NOX conversion efficiency, which is determined by the oxygen sensor concentration measurement values before and after the LNT post-treatment. O2 will be precipitated during the LNT reduction stage. When the oxygen concentrations before and after the LNT post-treatment are equal, it indicates that the DeNOx stage is completed.

[0027] Step 4) is as follows: The engine stops and stands still, allowing the hot HC compounds to naturally cool and deposit on the EGR valve; in this way, the hot and cold alternate, simulating the actual user usage state to create favorable conditions for the coking of the EGR valve. The standing still time is determined by the engine water temperature, and the engine water temperature naturally cools to 40 ± 2 °C.

[0028] Step 5) is as follows: Repeat steps 1) to 4) until the test is aborted when the EGR valve opening feedback value and the EGR valve voltage value are abnormal, or the engine emissions and performance parameters deteriorate by 5%.

[0029] Analysis of the Reasons for EGR Valve Coking in DeNOx Mode:

[0030] The composition structure of LNT uses alumina (Al2O3) as the carrier and Pt or Rh as the catalyst. The commonly used adsorption materials in LNT are alkaline earth metal oxides (BaCO3) or alkali metals (Na, K, Cs, etc.) oxides. The chemical reactions of LNT are very complex, mainly including the adsorption reaction in the trapping stage and the reduction reaction in the reduction stage. The working principle of LNT technology is a post-treatment technology that uses the change of the engine mixture concentration to perform periodic adsorption-catalytic reduction. Its reaction principle is that in the lean combustion state (more oxygen than fuel), the engine exhaust is in an oxidation environment. Under the catalytic action of platinum, NO in the engine exhaust reacts with O2 to form NO2 and is adsorbed on the surface of the catalytic converter in the form of nitrate. When the engine is in the rich combustion state (more fuel than oxygen), the content of HC compounds and CO in the engine exhaust increases, and the nitrate is decomposed to release NO X , and under the action of the catalyst rhodium, it reacts with CO, HC and H2 to form N2, CO2 and H2O, and regenerates the alkali metal.

[0031] Trapping stage: The trapping stage of LNT is to temporarily store the adsorbed NO X in the form of Ba(NO3)2 on the carrier, as Figure 1 shown, and its chemical reaction in the trapping stage is:

[0032] 2NO + O2 → 2NO2

[0033]

[0034] Reduction stage: The reduction stage of LNT, also known as the DeNOx stage, is to reduce the Ba(NO3)2 stored on the carrier to N2. To create the rich combustion environment required for reduction, generally, the method of post-injection in the cylinder or direct injection of fuel in the tailpipe is used to increase the content of HC compounds and CO in the exhaust gas. Its reduction reaction is:

[0035]

[0036]

[0037]

[0038] BaO + CO2 → BaCO3

[0039] During the reduction stage, HC compounds in the engine exhaust gas enter the engine combustion chamber through the EGR system, resulting in the deposition and coking of HC compounds and soot on the EGR valve. As the coking becomes more and more serious, problems such as EGR valve opening deviation and jamming will occur, affecting the engine performance, emissions and reliability. Therefore, when carrying out project development, it is necessary to design a test method for EGR valve coking to evaluate the coking risk of the EGR valve to ensure the reliability of the EGR coupled LNT system.

[0040] Compared with the prior art, the advantages of the present invention are as follows:

[0041] 1. Make full use of the characteristics of the LNT after-treatment technology, select the Pmax working condition and the DeNOx working condition to shorten the test time and save the test cost; increase the shutdown static time to simulate the actual vehicle use and provide conditions for EGR valve coking.

[0042] 2. This test method provides a verification means for EGR valve coking under the LNT after-treatment technology and can effectively evaluate the reliability of the EGR coupled LNT system.

[0043] The above are only the preferred embodiments of the present invention and do not impose any formal restrictions on the structure of the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An EGR valve coking test method under the DeNOx mode of an engine, characterized in that, It includes the following steps: 1) After the engine starts, it runs in the idle condition and warm-up condition for T0 time. 2) When the engine water temperature reaches normal, it can enter the LNT capture stage, i.e., run in the Pmax condition for T1 time. 3) After the NOx adsorption is settled, it enters the NOx reduction stage, i.e., run in the DeNOx condition for T2 time. 4) The engine idles and stops, and remains static until the engine water temperature drops to 40 ± 2 °C. 5) Repeat steps 1) to 4) until the test reaches the abort condition. Step 2) is as follows: In the LNT capture stage, the adsorbed NOX is temporarily stored on the carrier in the form of Ba(NO3)2. To accelerate the NOX adsorption and shorten the adsorption time, we select the rated power condition point Pmax where the engine generates the maximum NOX emission. The adsorption time T1 is determined by the NOX adsorption saturation degree, which is determined by the NOX sensor concentration measurement values before and after the LNT post-treatment. Step 3) is as follows: Utilize the engine DeNOx operating condition. At this time, the LNT is in the reduction stage. There are more HC compounds in the engine exhaust gas, which easily causes the EGR valve to coke, thus creating conditions for the EGR valve to coke. The operation time T2 in the reduction stage DeNOx condition is determined by the NOX conversion efficiency, which is determined by the oxygen sensor concentration measurement values before and after the LNT post-treatment. O2 will be precipitated in the LNT reduction stage. When the oxygen concentrations before and after the LNT post-treatment are equal, it indicates that the DeNOx stage is completed. Step 4) is as follows: The engine stops and remains static, allowing the hot HC compounds to naturally cool and deposit on the EGR valve. In this way, the hot and cold alternation simulates the actual user usage state and creates favorable conditions for the EGR valve to coke. The static time after stopping is determined by the engine water temperature, and the engine water temperature naturally cools to 40 ± 2 °C. Step 5) is as follows: Repeat steps 1) to 4) until the test is aborted when the EGR valve opening feedback value and the EGR valve voltage value are abnormal, or the engine emissions and performance parameters deteriorate by 5%.

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