Internal combustion power low NOx emission control method and device

Abstract

The invention discloses a control method and device for internal combustion power low NOx emission, and belongs to the technical field of tail gas aftertreatment. A flow sensor, an oxidation catalysis unit OC, an ammonia ejector, a nitrogen oxide storage unit NSRU, a nitrogen oxide concentration sensor and a selective catalytic reduction unit SCR are sequentially arranged in the exhaust direction. NOx in the tail gas firstly flows through the OC unit, NO in the tail gas is oxidized into NO2 by utilizing the oxidation characteristic of the OC unit, so that the concentration of NO2 in the tail gas is increased, and the NOx with the changed concentration ratio enters the NSRU unit; if the molar ratio of NH3 to NOx in the current NSRU region is lt; if 1, NO2 is partially converted into nitrate to be stored; if the molar ratio of NH3 to NOx in the current NSRU area is gt; if 1, the nitrate stored in the NSRU can be converted into NO2 to be released. Therefore, under the condition that the ammonia injection amount of the NSRU is constant, if the NOx of the incoming flow fluctuates in different heights, the NSRU adsorbs the NOx fluctuating in the forward direction and releases the NOx fluctuating in the negative direction, the stability of the flow of the NOx entering the SCR unit is improved, and efficient conversion of the NOx is achieved.

Description

Technical Field

[0001] This invention relates to the field of engine exhaust aftertreatment technology, and in particular to an aftertreatment method and apparatus that optimizes the intake composition of SCR by oxidizing nitric oxide (NO) to nitrogen dioxide (NO2) through an oxidation catalytic unit (OC), and uses a nitrogen oxide storage unit (NSRU) to dynamically adsorb and desorb NO2 according to the NH3 / NOx molar ratio to smooth mass flow fluctuations, thereby improving the treatment efficiency and control accuracy of the SCR system. Background Technology

[0002] With increasingly stringent environmental protection regulations, the requirements for controlling nitrogen oxide (NOx) emissions from engines are constantly rising, and achieving continuous and stable near-zero emissions has become a core industry goal. Selective catalytic reduction (SCR) technology is one of the most widely used and efficient denitrification solutions, which uses ammonia (NH3) to react with NOx in the presence of a catalyst to produce nitrogen and water. However, the traditional single-stage SCR technology faces two interrelated technical challenges in practice.

[0003] First, the reaction efficiency of an SCR system is limited by the intake air composition. Theoretical research and engineering practice show that the reaction pathway and efficiency of an SCR system are highly dependent on the ratio of nitric oxide (NO) to nitrogen dioxide (NO2) in NOx. When the concentration of NO2 increases, the system tends to follow the faster "fast SCR" pathway, improving NOx treatment efficiency. However, in the raw emissions of most engines, NO dominates (for example, the NO concentration in diesel engine exhaust can reach about 90%), while the proportion of NO2 is very low. This compositional relationship causes SCR systems to often operate under suboptimal reaction kinetics, limiting further improvements in their conversion efficiency.

[0004] Secondly, in actual operation, the NOx mass flow rate output by the engine exhibits drastic and high-frequency fluctuations. In traditional single-stage SCR systems, the ammonia injection rate must be precisely and rapidly adjusted to follow these fluctuations. Any delay or inaccuracy in control will lead to insufficient or excessive ammonia injection, resulting in incomplete NOx conversion and exceeding NOx limits, or ammonia escape causing secondary pollution. Therefore, effectively mitigating NOx mass flow rate fluctuations and providing a stable reaction environment for the SCR system is crucial for improving control accuracy and system reliability.

[0005] Against this backdrop, this invention enhances the traditional SCR system by pre-positioning an oxidation catalytic unit (OC) and a nitrogen oxide storage unit (NSRU). The OC is responsible for oxidizing NO to NO2, optimizing the SCR reaction composition; the NSRU dynamically adsorbs or releases NO2 based on the NH3 / NOx molar ratio, automatically mitigating mass flow rate fluctuations. Crucially, by placing the ammonia injection point after the OC, the risk of improper ammonia oxidation is avoided. This improves the system's NOx treatment efficiency and control precision, achieving highly efficient NOx conversion. Summary of the Invention

[0006] The purpose of this invention is to overcome the two major technical bottlenecks faced by traditional SCR aftertreatment systems: high NO concentration in the intake air composition and severe NOx mass flow rate fluctuations. It provides a method and device for controlling low NOx emissions from internal combustion engines. This system utilizes the NSRU's mechanism of storing positive fluctuations and releasing negative fluctuations in the incoming NOx mass flow rate to smooth out NOx fluctuations. It also works in conjunction with the OC's oxidation function for NO to create ideal intake conditions with high NO2 concentration and stable mass flow rate for the SCR reaction, thereby improving NOx purification efficiency and control reliability.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0008] A device for low NOx emissions from internal combustion engines, characterized in that it comprises a flow sensor, an oxidation catalytic unit (OC), an ammonia injector, a nitrogen oxide storage unit (NSRU), a nitrogen oxide sensor, a selective catalytic reduction unit (SCR), and an electronic control unit (ECU) connected sequentially along the exhaust gas flow direction.

[0009] The oxidation catalytic unit OC is configured to utilize its oxidation characteristics to efficiently oxidize NO in the exhaust gas to NO2, thereby increasing the concentration ratio of NO2 in the exhaust gas.

[0010] The ammonia injector is positioned between the oxidation catalytic unit OC and the nitrogen oxide storage unit NSRU. This arrangement avoids the risk of ammonia being oxidized by OC to generate NOx.

[0011] The nitrogen oxide storage unit (NSRU) is configured to operate dynamically based on the NH3 / NOx molar ratio of its internal environment: when the molar ratio is less than 1, NO2 is partially converted into nitrate and stored; when the molar ratio is greater than 1, the nitrate stored inside is converted into NO2 and released. This mechanism enables the NSRU to adsorb positive NOx fluctuations and release negative NOx fluctuations in the incoming flow, thus smoothing out mass flow rate fluctuations, under the condition of constant ammonia injection rate.

[0012] The flow sensor is located downstream of the engine exhaust manifold and is used to measure the total mass flow rate of exhaust gas [Q0].

[0013] The nitrogen oxide sensor is disposed between the nitrogen oxide storage unit (NSRU) and the selective catalytic reduction unit (SCR) and is used to measure the nitrogen oxide concentration after stabilization [C]. NOx ;

[0014] The electronic control unit (ECU) is connected to the flow sensor, nitrogen oxide sensor, and ammonia injector signal, and is configured to execute unified ammonia injection control logic.

[0015] Furthermore, the catalyst of the oxidation catalytic unit OC is preferably a noble metal catalyst, and the storage material of the nitrogen oxide storage unit NSRU is preferably an alkali metal or alkaline earth metal oxide.

[0016] Furthermore, the unified control logic executed by the electronic control unit (ECU) is characterized by being based on the mass flow rate [Q0] and the reduced nitrogen oxide concentration [C]. NOx The injection rate of the ammonia injector is calculated and controlled using a fixed ammonia-nitrogen stoichiometric ratio of 1.1:1.

[0017] The unified control logic specifically includes the following steps:

[0018] S1. Real-time acquisition of total exhaust gas mass flow rate [Q0] and nitrogen oxide concentration [C] after NSRU suppression. NOx ;

[0019] S2, according to the formula (1) Calculate the required ammonia injection mass flow rate, where α is the molar mass conversion factor between NH3 and NOx;

[0020] S3. Based on the standard, fast, and slow reaction chemical formulas in the SCR unit reaction, the molar mass conversion coefficient α between NH3 and NOx conforms to the value pattern shown in equation (2): (2) In the formula [C NO ] and [C NO2 [ ] represents the concentrations of NO and NO2 in the exhaust gas flowing through the SCR, respectively.

[0021] S4. Based on the calculation results [Q] NH3 ] input Control the ammonia injector to inject.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) This invention constructs a front-end unit of OC+NSRU to serve the core of SCR unit. By arranging the ammonia injector downstream of OC, the technical contradiction of ammonia being oxidized by OC is completely solved from the hardware layout, providing a foundation for the efficient utilization of ammonia.

[0024] (2) The OC unit actively optimizes the intake composition of SCR, significantly increasing the NO2 ratio and creating the necessary conditions for efficient and rapid SCR reaction. At the same time, through the dynamic storage and release of NOx by the NSRU unit, the fluctuation of NOx in the SCR intake is passively suppressed, providing stable conditions for implementing precise and simple ammonia injection control. The synergy between OC and NSRU, from the two dimensions of reaction kinetics and process control, jointly ensures and improves the conversion efficiency and operational reliability of the SCR unit.

[0025] (3) This system inherits mature technical components in the field of diesel engine aftertreatment, with good technical inheritance and controllable modification costs. The stable, efficient and low-escape emission control effect it provides is especially suitable for commercial vehicle diesel engines with complex operating conditions, providing a technical path to meet more stringent emission regulations. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the system structure of the present invention.

[0027] Figure 2 This is a schematic diagram of the existing system architecture; Figure 3 This is a schematic diagram of the system node effect of the present invention.

[0028] Figure 4 This is a flowchart of the control method of the present invention. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] like Figure 1 The schematic diagram of the hardware equipment of the present invention is shown. The hardware connection relationship of the control method and device for low NOx emissions of internal combustion power is as follows: the exhaust manifold (1) of the diesel engine is connected to the inlet of the oxidation catalytic unit OC (2). The front end of the oxidation catalytic unit OC (2) is equipped with a flow sensor (Q0), and its outlet is connected in sequence to an ammonia injector (3) and a nitrogen oxide storage unit NSRU (4). The outlet of the nitrogen oxide storage unit NSRU (4) is connected in sequence to a nitrogen oxide sensor (C1) and a selective catalytic reduction unit SCR (5). The electronic control unit ECU (6) is connected to all sensors (Q0, C1) and the ammonia injector (3) through a wiring harness to form a control system.

[0031] To more clearly illustrate the implementation effects of the present invention, in conjunction with Figure 2 The diagram illustrates the comparison between a traditional single-stage SCR system and the three-stage processing system described in this invention. Figure 2 The curves showing the change in nitrogen oxide mass flow rate at different monitoring points for the two systems under the same engine exhaust gas fluctuation conditions are presented.

[0032] Before the inlet of the oxidation catalytic unit OC (2) (monitoring point 1-1), the two systems respond to the same original emission characteristics of the engine: the mass flow rate of nitrogen oxides shows violent and high-frequency fluctuations, and its components are mainly NO.

[0033] After passing through the oxidation catalytic unit OC (2) (monitoring point 2-1), the NO concentration in the exhaust gas decreases, and NO2 becomes the main component. At monitoring point 2-1, the mass flow rate fluctuation of the three-stage system is basically consistent with that of the conventional system at the corresponding location (monitoring point 2-2). The core function of the oxidation catalytic unit OC (2) is to oxidize NO in the exhaust gas, but it does not have the ability to smooth out flow rate fluctuations.

[0034] At the outlet of the nitrogen oxide storage unit NSRU (4) (monitoring point 3-1), the nitrogen oxide mass flow rate curve is flattened and the fluctuations are suppressed. Correspondingly, the nitrogen oxide mass flow rate curve of the single-stage SCR system at the SCR inlet (monitoring point 3-2) still maintains the violent fluctuation characteristics of the original engine exhaust.

[0035] At the end of the three-stage system (monitoring point 4-1), thanks to the stable intake environment provided by the NSRU (4), the final nitrogen oxide mass flow rate is stable and consistently lower than the limit stipulated by national regulations. In contrast, due to the fluctuation of nitrogen oxide mass flow rate at the SCR inlet of the single-stage SCR system, the ammonia injection control is difficult to keep up with in real time, and the emission curve at the end (monitoring point 4-2) will repeatedly show instantaneous exceedances of regulatory limits at the peak.

[0036] Combination Figure 1 and Figure 4 The control flowchart shown below provides a detailed explanation of the operation process of the control system of this application. The ECU (6) executes the following control logic:

[0037] S1. Real-time acquisition of the concentration of nitrogen oxide sensor C1 [C1] NOx The exhaust gas flow rate [Q0] of the front-end flow sensor Q0 of the oxidation catalytic unit OC (2).

[0038] S2, based on [C1] NOxThe ECU (6) uses a feedforward control method to directly calculate the injection rate of the ammonia injector (3). The control objective is to maintain the NH3 / NOx molar ratio at a stable 1.1:1, which is slightly higher than the theoretical value of 1:1. This aims to ensure high conversion efficiency while reserving a certain safety margin. In the formula, α is the molar mass conversion coefficient of NH3 and NOx in the SCR reaction, and the ammonia injection mass flow rate [Q] is... NH3 ] input The calculation formula is:

[0039] (1)

[0040] S3. Based on the standard, fast, and slow reaction chemical formulas in the SCR unit reaction, the molar mass conversion coefficient α between NH3 and NOx conforms to the value pattern shown in equation (2): (2) In the formula [C NO ] and [C NO2 [ ] represents the concentrations of NO and NO2 in the exhaust gas flowing through the SCR, respectively.

[0041] S4. Based on the calculation results [Q] NH3 ] input Control the ammonia injector to inject.

[0042] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this application are indicated by the claims.

[0043] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this application. This application is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A device for low NOx emissions from internal combustion engines, installed on an exhaust pipe, characterized in that, It includes a flow sensor, oxidation catalytic unit (OC), ammonia injector, nitrogen oxide storage unit (NSRU), nitrogen oxide sensor, selective catalytic reduction unit (SCR), and electronic control unit (ECU) connected sequentially along the exhaust direction. The ammonia injector is located between the oxidation catalytic unit OC and the nitrogen oxide storage unit NSRU, and is controlled by the electronic control unit ECU. The flow sensor is located downstream of the engine exhaust manifold and is used to measure the total mass flow rate of exhaust gas [Q0]. The nitrogen oxide sensor is disposed between the nitrogen oxide storage unit (NSRU) and the selective catalytic reduction unit (SCR) and is used to measure the nitrogen oxide concentration at the back end of the NSRU. The electronic control unit (ECU) is connected to the ammonia injector and configured to: base its signal on the flow rate [Q0] measured by the flow sensor and the concentration [C] measured by the nitrogen oxide sensor. NOx The mass flow rate of nitrogen oxides is calculated, and the injection rate of the ammonia injector is controlled accordingly with a fixed ammonia-nitrogen stoichiometric ratio.

2. The apparatus according to claim 1, characterized in that, The oxidation catalytic unit OC is configured to utilize its oxidation properties to oxidize nitric oxide (NO) in the exhaust gas to nitrogen dioxide, thereby increasing the concentration ratio of NO2 in the exhaust gas; and the ammonia injector is placed downstream of the OC to prevent ammonia from being oxidized by the OC; the catalyst of the OC is a noble metal catalyst.

3. The apparatus according to claim 1, characterized in that, The nitrogen oxide storage unit (NSRU) is configured to operate dynamically based on the NH3 / NOx molar ratio in its internal environment: when the molar ratio is less than 1, NO2 is converted into nitrate and stored; when the molar ratio is greater than 1, the stored nitrate is converted into NO2 and released. Through this mechanism, under the condition of constant ammonia injection, if the incoming NOx fluctuates, the NSRU will adsorb the positively fluctuating NOx and release the negatively fluctuating NOx, thereby improving the stability of the NOx flow rate entering the SCR unit. The catalyst of the NSRU is an alkali metal or alkaline earth metal oxide.

4. A method for controlling the apparatus as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Based on the data from the flow sensor and the nitrogen oxide sensor, obtain the total mass flow rate of the exhaust gas [Q0] and the nitrogen oxide concentration [C] after NSRU suppression in real time. NOx ; S2. Based on the total exhaust gas mass flow rate [Q0] and the nitrogen oxide concentration [C] NOx Calculate the required ammonia injection mass flow rate (1); S3, where α is the molar mass conversion factor between NH3 and NOx: （2） Among them [C] NO ] and [C NO2 [ ] These represent the concentrations of NO and NO2 in the exhaust gas flowing through the SCR, respectively; S4. The electronic control unit (ECU) obtains [Q] based on the calculation results. NH3 ] input This controls the ammonia injector to spray.

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