NOx after-treatment system for hydrogen engine and regulation and control method of NOx after-treatment system

Abstract

The invention provides a hydrogen engine tail gas NOx aftertreatment system and a regulation and control method thereof. The system is based on the NOx storage-reduction (NSR) technology, the hydrogen concentration in tail gas is actively adjusted through a hydrogenation nozzle on a tail pipe, NOx is stored in a dilute hydrogen state, and hydrogen spraying is switched to a hydrogen-rich state to reduce NOx. A NOx concentration sensor is installed at an outlet of a catalytic box to measure NOx concentration CNOx and oxygen concentration CO2, a hydrogen concentration sensor is used for measuring hydrogen concentration CH2, and when CNOx is larger than the CNOx limit, NOx storage is full, and hydrogen spraying is started. A flow meter is installed in front of a hydrogen nozzle to monitor the tail gas flow QE, and a hydrogen spraying strategy is formulated according to the oxygen concentration CO2 (volume ratio). When CO2 is larger than or equal to 0.5%, in order to avoid hydrogen-oxygen mixed burning explosion (the combustible limit is 4% CO2), the hydrogen injection concentration is set to be 3% of CO2, and the hydrogen injection amount QH2 is equal to 3% CO2QE; and when CO2 is smaller than 0.5%, QH2 is adjusted to be equal to 1% QE, and accurate adjustment is performed through pulse width and frequency. And when CH2 is larger than CH2, hydrogen spraying is stopped after reduction is completed. The CNOx limit and the CH2 limit are the nitrogen oxide emission limit and the hydrogen leakage limit.

Description

Technical Field

[0001] The invention belongs to the technical field of automobile exhaust aftertreatment, and in particular relates to a hydrogen injection control device and method for an exhaust aftertreatment system for a hydrogen engine. Background Art

[0002] The global consensus on the future society has completed the transition from low carbon to net zero carbon, and carbon neutrality has become the focus of global social efforts. Hydrogen energy is an important carrier for energy-using terminals to achieve green and low-carbon transformation. As one of the important forms of hydrogen energy application, hydrogen engines are clean and efficient, meeting the needs of global energy conservation, emission reduction and low-carbon development. As countries become increasingly stringent in environmental protection regulations, traditional engines face emission restrictions, while hydrogen, as a clean energy source, only produces water vapor as a combustion product and does not produce harmful gases. Therefore, hydrogen engines have broad application potential in transportation, industrial machinery, power generation and other fields. Especially in the field of transportation, hydrogen fuel cells and hydrogen engines provide a feasible solution for achieving zero emissions and long endurance, which is driven by government policy support and market demand. In addition, the gradual development of hydrogen storage and transportation technology has also created favorable conditions for the popularization and application of hydrogen engines.

[0003] Because the combustion of hydrogen in the engine will cause engine knock, high detonation pressure and thermal efficiency. At present, the lean burn strategy is mainly adopted to reduce the maximum combustion temperature in the cylinder and reduce the generation of NOx. Nitrogen oxides (NOx) are one of the main pollutants emitted by motor vehicles. They are at the core of the formation of regional complex air pollution and are closely related to the formation of photochemical smog and haze, two typical atmospheric complex pollution. For NOx removal under oxygen-rich conditions, common methods include NOx catalytic decomposition, selective catalytic reduction technology (SCR) and NOx storage reduction technology (NSR). SCR technology requires the configuration of urea tanks and urea injection systems, and urea will be crystallized and thawed at low temperatures, and ammonia leakage may also occur.

[0004] Nitrogen oxide storage reduction technology was first proposed by Toyota in Japan in the mid-1990s to solve the problem of nitrogen oxides in automobile emissions. This technology reduces NOx emissions in exhaust gas by storing nitrogen oxides on the catalyst surface and converting them into harmless nitrogen and oxygen through reduction reactions at the right time. The storage reduction catalyst in NSR technology works under lean / rich hydrogen switching. Under lean combustion conditions of the engine, the exhaust gas does not contain hydrogen and is in a lean hydrogen state. The oxygen in the exhaust gas is sufficiently excessive and can effectively react with nitrogen oxides, resulting in NOx components being adsorbed and stored on the catalyst. At this time, the active sites on the catalyst adsorb NOx molecules; when the reducing agent H is sprayed into the engine exhaust gas, the NOx molecules are adsorbed on the catalyst. 2, that is, the exhaust gas enters a hydrogen-rich state, and the stored NOx is reduced to harmless N by the reduction reaction with hydrogen. 2 and O 2 . During the operation of this NSR, the control of the amount of hydrogen injection will effectively regulate the lean and rich hydrogen state of the exhaust gas. 2 Real-time monitoring of concentration enables precise control of the start and stop of hydrogen injection, making NSR post-treatment of hydrogen engine exhaust safer and more efficient. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a hydrogen injection control device and method for a hydrogen engine exhaust aftertreatment system (NSR). NSR converts NOx into N by adsorbing and reducing NOx. 2 and H 2 O, tail gas enters the post-processing device from the exhaust pipe, a flow sensor and a hydrogen supply system are arranged at the front end of the post-processing device, a NOx concentration sensor and a hydrogen concentration sensor are arranged at the exhaust pipe at the end of the post-processing device, and the post-processing device includes an electronic control unit for receiving and feeding back signals, and the electronic control unit is connected with the flow sensor, the hydrogen nozzle, the hydrogen pressure sensor, the NOx sensor, and the hydrogen concentration sensor signal. The present invention can achieve NOx emission reduction of hydrogen engines under different combustion conditions, accurately control the hydrogen injection amount and injection pulse width, and more efficiently process NOx in tail gas.

[0006] In order to achieve the above technical objectives, the technical solution adopted in the implementation of the present invention is: In a first aspect, an embodiment of the present invention provides an exhaust gas after-treatment device for a hydrogen engine, wherein the NSR system is a NOx storage and reduction device that achieves storage and reduction of NOx, and the exhaust gas is discharged from the engine and enters the after-treatment device. A flow sensor is arranged in front of the NSR system to detect the exhaust gas flow. A hydrogen supply system is arranged behind the flow sensor and in front of the NSR system for injecting hydrogen into the NSR system. A NOx concentration sensor is arranged at the rear of the NSR system to detect the NOx concentration and oxygen concentration at the NSR outlet. A hydrogen concentration sensor is arranged at the rear end of the NOx concentration sensor to measure the hydrogen concentration at the NSR outlet. The post-processing device also includes an electronic control unit for receiving and feeding back signals, and the electronic control unit is connected to a flow sensor, a hydrogen nozzle, a hydrogen pressure sensor, a NOx concentration sensor, and a H 2 Concentration sensor connection, used to receive exhaust gas flow, hydrogen pressure, NOx concentration at the rear end of the NSR system, O2 Concentration and H 2 concentration, calculate the hydrogen injection demand, and control the opening and closing of the hydrogen nozzle.

[0007] Furthermore, the interior of the NSR is Pt / BaO / Al 2 O 3 The catalyst has an average pore size of about 5-8nm, a specific surface area of ​​180-220m2 / g, and a pore volume of about 0.7-1.2cm3 / g, forming a honeycomb porous network. BaO is loaded on the inner wall of the pores in the form of nanoparticles, accounting for 10-15wt%, for NOx chemical adsorption; the Pt active component (0.5-1.5wt%) is evenly anchored on the BaO surface by impregnation, and the particle size is controlled at 2-5nm, which is used to adsorb and reduce NOx entering the NSR, adsorbing NOx under lean combustion conditions and reducing NOx under rich combustion conditions.

[0008] In a second aspect, an embodiment of the present invention provides a hydrogen injection control device and method for an exhaust gas aftertreatment system for a hydrogen engine, comprising the following steps: Step 1: The NOx concentration sensor detects the NOx concentration C at the end of the NSR NOx and oxygen concentration C O2 When the terminal NOx sensor detects that the terminal NOx concentration is greater than C NOx限 Then start to spray hydrogen. NOx限 The nitrogen oxide emission limit should be calibrated by the manufacturer according to the national emission standards based on the vehicle model and operating conditions. Step 2: The hydrogen pressure sensor detects the current hydrogen pressure, and the flow sensor and NOx concentration sensor detect the exhaust flow Q E and oxygen concentration C O2 , is fed back to the electronic control unit, which determines the calculation method of the hydrogen injection amount based on whether the oxygen concentration is greater than 0.5%. When the oxygen concentration is greater than or equal to 0.5%, the required hydrogen injection amount is calculated by the formula Q H2 =3%C O2 Q E Calculation shows that when the oxygen concentration is less than 0.5%, the required hydrogen injection amount is calculated by Q H2 =1%Q E The electronic control unit dynamically controls the hydrogen nozzle by adjusting the injection pulse width and frequency of the hydrogen nozzle to accurately meet the real-time hydrogen injection demand. Step 3: H 2 The concentration sensor detects the NSR terminal H 2 Content, if greater than C H2限 If the hydrogen spraying stops, the hydrogen spraying will continue. H2限 It is the hydrogen leakage limit and should be calibrated by the manufacturer according to the national emission standards based on the vehicle model and operating conditions.

[0009] The beneficial effects of the technical solution provided by the embodiment of the present invention are: 1. Use NSR system to treat the exhaust gas of hydrogen engine. 2 It is directly provided by the on-board hydrogen storage system, without the need for an additional urea tank, saving space costs and avoiding ammonia leakage and urea crystallization. 2. The hydrogen nozzle is set at the front end of the NSR, which is beneficial to the NOx desorption of the NSR catalyst. 3. The electronic control unit is based on the exhaust gas flow rate and the terminal NOx concentration O 2 The concentration and hydrogen concentration determine when to start hydrogen injection and the required hydrogen injection amount Q H2 =3%C O2 Q E or Q H2 =1%Q E When to stop injecting hydrogen, according to H 2 A pressure sensor is arranged at the front end of the nozzle to detect the hydrogen pressure and quickly respond to NOx and H 2 The concentration changes to precisely control the hydrogen injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of the structure of the hydrogen engine exhaust after-treatment device in an embodiment of the present invention.

[0011] Figure 2 This is a control schematic diagram of the hydrogen injection strategy of the hydrogen engine exhaust aftertreatment device in an embodiment of the present invention.

[0012] Figure 3 This is a control flow chart of the hydrogen injection strategy of the hydrogen engine exhaust after-treatment device in an embodiment of the present invention.

[0013] Explanation of reference numerals: 1-flow sensor, 2-hydrogen nozzle; 3-hydrogen pressure sensor; 4-control unit; 5-NOx storage reduction system; 6-NOx concentration sensor; 7-H 2 Concentration sensor. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0015] Example 1 like Figure 1 As shown, an exhaust gas aftertreatment device for a hydrogen engine includes a NOx storage reduction system (NSR) sequentially arranged in an exhaust pipe of the hydrogen engine, and the exhaust gas enters the aftertreatment device after being discharged from the exhaust pipe of the engine; A flow sensor (1) and a hydrogen nozzle (2) are arranged at the front exhaust pipe of the NSR. The hydrogen nozzle (2) is connected to the vehicle-mounted hydrogen storage system. A hydrogen pressure sensor (3) is arranged at the front end of the hydrogen nozzle for monitoring the hydrogen supply pressure. A NOx concentration sensor (6) is arranged at the rear of the NSR system to detect the NOx concentration and O 2 concentration. A hydrogen concentration sensor (7) is arranged after the NOx concentration sensor to measure the H concentration at the NSR outlet. 2 concentration. The post-processing device further comprises an electronic control unit (4) for receiving and feeding back signals, wherein the electronic control unit (4) is connected to the flow sensor (1), the hydrogen nozzle (2), the hydrogen pressure sensor (3), the NOx concentration sensor (6), and the hydrogen concentration sensor (7), and is used to receive exhaust gas flow, hydrogen pressure, NOx at the rear end of the NSR system, and NOx at the rear end of the NSR system. 2 and H 2 concentration, calculate the hydrogen injection demand, and control the opening and closing of the hydrogen nozzle.

[0016] NSR interior is Pt / BaO / Al 2 O 3 Based catalyst, H 2 It is a reducing agent, which is injected into the catalyst box by the hydrogen nozzle in front of the catalyst box to store and reduce the NOx generated by the hydrogen engine.

[0017] Pt-based catalysts are usually supported on a porous alumina (Al 2 O 3 ) is coated with barium oxide (BaO) and platinum (PT). The average pore size is about 5-8nm, and the specific surface area is 180-220m 2 / g, pore volume about 0.7-1.2cm 3 / g, forming a honeycomb porous network. BaO is loaded on the inner wall of the pores in the form of nanoparticles, accounting for 10-15wt%, for NOx chemical adsorption; Pt active components (0.5-1.5wt%) are evenly anchored on the BaO surface by impregnation, and the particle size is controlled at 2-5nm.

[0018] Example 2 like Figure 2 As shown, a hydrogen injection control device and method for an exhaust gas aftertreatment system for a hydrogen engine comprises the following steps: Step 1: The NOx concentration sensor (6) detects the NOx concentration C at the end of the NSR. NOx and oxygen concentration C O2 When the terminal NOx sensor (6) detects that the terminal NOx concentration is greater than C NOx限Then start to spray hydrogen. NOx限 The nitrogen oxide emission limit should be calibrated by the manufacturer according to the national emission standards based on the vehicle model and operating conditions. Step 2: The hydrogen pressure sensor (3) detects the current hydrogen pressure, and the flow sensor and NOx concentration sensor detect the exhaust gas flow Q E and oxygen concentration C O2 , is fed back to the electronic control unit (4), and the electronic control unit (4) determines the calculation method of the hydrogen injection amount according to whether the oxygen concentration is greater than 0.5%. When the oxygen concentration is greater than or equal to 0.5%, the required hydrogen injection amount is calculated by the formula Q H2 =3%C O2 Q E Calculation shows that when the oxygen concentration is less than 0.5%, the required hydrogen injection amount is calculated by Q H2 =1%Q E The electronic control unit dynamically controls the hydrogen nozzle by adjusting the injection pulse width and frequency of the hydrogen nozzle to accurately meet the real-time hydrogen injection demand. Step 3: H 2 The concentration sensor (7) detects the NSR terminal H 2 Content, if greater than C H2限 If the hydrogen spraying stops, the hydrogen spraying will continue. H2限 It is the hydrogen leakage limit and should be calibrated by the manufacturer according to the national emission standards based on the vehicle model and operating conditions.

[0019] The chemical equations for the reactions of the exhaust gas flowing through the NSR include equations (1) to (4): NO 2 +MO→MNO 3 (2) Where M represents a metal element

[0020] In summary, the present invention provides a hydrogen injection control device and method for a hydrogen engine exhaust aftertreatment system (NSR). The aftertreatment device of the present invention is an NSR, which adsorbs and reduces NOx in the engine exhaust under lean combustion conditions. 2 Under adsorption conditions, concentrated H 2Reduction under conditions; a flow sensor and a hydrogen supply system are set at the front end of the post-processing device, and a NOx concentration sensor and a hydrogen concentration sensor are set at the exhaust pipe at the end of the post-processing device. The post-processing device includes an electronic control unit for receiving and feeding back signals. The electronic control unit is connected with the flow sensor, hydrogen nozzle, hydrogen pressure sensor, NOx concentration sensor, and hydrogen concentration sensor signal. Accurately control the hydrogen injection amount and injection pulse width to more efficiently treat NOx in the exhaust gas. Compared with the SCR system, no additional urea injection system is required. Compared with the ordinary NSR system, a flow sensor is added, and the terminal NOx and H 2 Concentration sensor reduces NOx overflow, accurately controls hydrogen injection amount and start and stop timing, improves equipment operation efficiency and reduces operating costs.

Claims

1. A NOx post-treatment system for a hydrogen engine, characterized in that: The invention comprises a NOx storage reduction system (NSR) which is sequentially arranged in the exhaust pipe of a hydrogen engine, wherein a flow sensor (1) and a hydrogen nozzle (2) are arranged in the exhaust pipe at the front end of the NSR, the hydrogen nozzle (2) is connected to the vehicle-mounted hydrogen storage system, and a hydrogen pressure sensor (3) is arranged at the front end of the hydrogen nozzle; A NOx sensor (6) is arranged at the rear of the NSR to detect the NOx emission concentration and oxygen concentration at the NSR outlet; A hydrogen concentration sensor (7) is arranged after the NOx sensor to measure the hydrogen concentration at the NSR outlet; The invention also comprises an electronic control unit (4) for receiving and feeding back signals. The electronic control unit (4) is connected to the flow sensor (1), the hydrogen nozzle (2), the hydrogen pressure sensor (3), the NOx concentration sensor (6), and the hydrogen concentration sensor (7), and is used to receive the exhaust gas flow, the hydrogen pressure, the NOx concentration and the hydrogen concentration at the rear end of the NSR system, calculate the hydrogen injection demand, and control the opening and closing of the hydrogen nozzle.

2. The post-processing system according to claim 1, characterized in that: The NOx storage reduction system, i.e., NSR, contains Pt / BaO / Al2O3 as catalyst, with an average pore size of about 5-8nm and a specific surface area of ​​180-220m 2 / g, pore volume 0.7-1.2cm 3 / g; BaO is loaded on the inner wall of the pores in the form of nanoparticles, accounting for 10-15wt%, for NOx chemical adsorption; the Pt active component content is 0.5-1.5wt%, which is evenly anchored on the BaO surface by impregnation method, and the particle size is controlled at 2-5nm; H2 is the reducing agent, which is injected into the catalyst box by the hydrogen nozzle in front of the catalyst box to treat NOx generated by the hydrogen engine.

3. The method for controlling hydrogen injection of a post-treatment system according to claim 1 or 2, characterized in that: The following steps are involved: Step 1: The NOx concentration sensor (6) detects the NOx concentration C at the end of the NSR. NOx and oxygen concentration C O2 When the terminal NOx sensor (6) detects that the terminal NOx concentration is greater than C NOx限 Then start to spray hydrogen; C NOx限 is the emission limit of nitrogen oxides; Step 2: The hydrogen pressure sensor (3) detects the current hydrogen pressure, and the flow sensor and NOx concentration sensor detect the exhaust gas flow Q E and oxygen concentration C O2 , is fed back to the electronic control unit (4), and the electronic control unit (4) determines the calculation method of the hydrogen injection amount according to whether the oxygen concentration is greater than 0.5%; when the oxygen concentration is greater than or equal to 0.5%, the required hydrogen injection amount is calculated by the formula Q H2 =3%C O2 Q E Calculation shows that when the oxygen concentration is less than 0.5%, the required hydrogen injection amount is calculated by Q H2 =1%Q E The electronic control unit adjusts the injection pulse width and frequency of the hydrogen nozzle; Step 3: The H2 concentration sensor (7) detects the H2 content at the end of the NSR. If it is greater than C H2限 If the hydrogen spraying stops, otherwise it continues; C H2限 It is the hydrogen leakage limit.

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