A natural gas engine internal exhaust gas recirculation exhaust heat management system

Abstract

The utility model relates to the technical field of engine exhaust, and disclose a kind of exhaust heat management system of internal exhaust gas recirculation of natural gas engine, including engine body, the engine body is equipped with variable hydraulic valve mechanism, for producing internal exhaust gas recirculation by exhaust valve secondary opening;Aftertreatment unit is sequentially arranged with TWC, DOC, DPF and SCR along exhaust flow direction, and the upstream of TWC and SCR is equipped with urea nozzle.The utility model can accurately control exhaust valve secondary opening by full variable hydraulic valve mechanism, under medium load condition, part of exhaust gas is reintroduced into cylinder, which reduces oxygen concentration and combustion temperature in cylinder, reduces NOx original emission, and through high-temperature exhaust gas mixing to improve exhaust temperature, which lays foundation for efficient work of aftertreatment system, without external pipeline and cooler, reduces pumping loss, thereby improves engine thermal efficiency, reduces gas consumption rate, and gives consideration to emission reduction and energy saving.

Description

Technical Field

[0001] This utility model relates to the field of engine exhaust technology, specifically to an exhaust heat management system for internal exhaust gas recirculation in a natural gas engine. Background Technology

[0002] With increasingly stringent national environmental regulations, meeting the China VI emission standard has become an inevitable requirement for the development of high-horsepower natural gas engines. Currently, the industry generally adopts a technical approach of "Exhaust Gas Recirculation (EGR) + Three-Way Catalytic Converter (TWC) + Selective Catalytic Reduction (SCR)" to address emission limits for nitrogen oxides (NOx) and particulate matter (PM). However, traditional exhaust thermal management methods, such as intake throttle valve adjustment, turbocharger optimization, and electronic fuel injection (ECI) strategies, have significant limitations in practical applications. These methods primarily increase exhaust temperature by sacrificing some engine performance (such as increasing pumping losses), which not only fails to significantly improve engine thermal efficiency but also faces challenges in the accuracy and efficiency of emission control, especially exhibiting lag in response under transient conditions, making it impossible to simultaneously meet the dual demands of energy conservation, emission reduction, and power performance.

[0003] Exhaust gas recirculation (EGR) technology, as an effective means of reducing NOx emissions, can be divided into two implementation methods: internal EGR and external EGR. External EGR systems introduce a portion of exhaust gas into the intake system through independent EGR valves, coolers, and piping. While effective, this approach increases system complexity and failure rate, and the cooled exhaust gas has limited effect on raising exhaust temperature, which is detrimental to the regeneration of the subsequent power filter (DPF). Internal EGR, on the other hand, achieves exhaust gas recirculation within the engine through valve control strategies. It requires no additional hardware, has a compact structure, and responds quickly. Traditional internal EGR often relies on camshaft phaser adjustments, but its adjustment range is limited, failing to achieve continuous variable control of valve lift and opening duration, thus restricting the full realization of its performance potential.

[0004] The emergence of Fully Variable Hydraulic Valve System (FHVVS) technology provides a new solution for achieving internal EGR. FHVVS can independently and continuously control the valve opening phase, lift, and duration through a hydraulic control system, laying the technological foundation for more flexible and precise internal EGR control. For natural gas engines with slower combustion speeds and higher ignition temperatures, FHVVS technology can optimize the combustion process by implementing strategies such as the Miller cycle. Simultaneously, its precise valve control capability creates conditions for achieving internal EGR through "secondary exhaust valve opening," thereby effectively increasing exhaust temperature while reducing primary NOx emissions. This is significant for improving the efficiency of aftertreatment systems and reducing urea consumption.

[0005] However, how to deeply integrate and coordinately control advanced FHVVS technology with a complete aftertreatment system (TWC-DOC-DPF-SCR) to build an efficient, reliable, and all-condition adaptable exhaust thermal management system remains a technical challenge for those skilled in the art. Existing systems often fail to effectively link engine source control and end-of-pipe purification, and cannot maximize the comprehensive benefits of internal EGR in improving thermal efficiency, reducing emissions, and promoting DPF regeneration.

[0006] Therefore, developing an internal exhaust gas recirculation thermal management system based on FHVVS is of urgent practical significance and important application value for promoting the technological advancement of high-horsepower natural gas engines and meeting more stringent requirements. Utility Model Content

[0007] To address the technical problems existing in the background art, this utility model proposes an exhaust gas recirculation thermal management system for a natural gas engine.

[0008] This utility model proposes an exhaust gas recirculation thermal management system for a natural gas engine, comprising: The engine body is equipped with a variable hydraulic valve mechanism for generating internal exhaust gas recirculation by opening the exhaust valve a second time. The aftertreatment unit is arranged in series along the exhaust flow direction, including TWC, DOC, DPF and SCR, and urea nozzles are provided upstream of TWC and SCR. The control unit is used to drive the variable hydraulic valve mechanism to perform secondary opening of the exhaust valve under medium load conditions, so as to reintroduce some exhaust gas into the cylinder, increase the exhaust temperature and reduce the original NOx emissions.

[0009] As a further optimization of this utility model, NOx sensors are provided upstream of the TWC and downstream of the SCR. The former sensor is used to measure the original NOx emissions of the engine, and the latter sensor provides a closed-loop signal for the SCR to correct the urea injection quantity in a closed loop and improve the SCR conversion efficiency.

[0010] As a further optimization of this utility model, the NOx sensor downstream of the SCR inputs a signal to the on-board diagnostic system for dual diagnosis of EGR rate deviation and urea injection deviation.

[0011] As a further optimization of this utility model, the control unit is set with an EGR rate map, the EGR rate is controlled within the range of 5% to 35%, and is adjusted in real time according to the speed and load.

[0012] As a further optimization of this utility model, when the DPF differential pressure is greater than the set threshold and the SCR inlet temperature is greater than 480°C, the control unit uses internal EGR heating regeneration instead of triggering HC active regeneration.

[0013] As a further optimization of this utility model, the variable hydraulic valve mechanism is an FHVVS fully variable hydraulic valve mechanism, which can realize stepless adjustment of the exhaust valve's secondary opening lift and phase within the same cycle.

[0014] As a further optimization of this utility model, no HC injector is provided between the DOC and the DPF, and the exhaust temperature is met by the internal EGR alone.

[0015] As a further optimization of this utility model, a differential pressure sensor is installed on the DPF to measure the airflow resistance of the DPF.

[0016] As a further optimization of this utility model, temperature sensors are installed downstream of the TWC and upstream and downstream of the SCR. The urea injection system calculates the required urea injection amount based on the temperature of the TWC and SCR catalysts.

[0017] As a further optimization of this utility model, the control unit is an on-board ECU.

[0018] The exhaust gas recirculation thermal management system for natural gas engines proposed in this invention has the following beneficial effects: (i) Breakthrough achieved through “variable hydraulic valve mechanism + internal EGR” design: The engine body can precisely control the secondary opening of the exhaust valve through the fully variable hydraulic valve mechanism, and reintroduce some exhaust gas into the cylinder under medium load conditions. This reduces the oxygen concentration and combustion temperature in the cylinder, thereby reducing the original NOx emissions. At the same time, the high-temperature exhaust gas mixture increases the exhaust temperature, laying the foundation for the efficient operation of the aftertreatment system. Meanwhile, the internal EGR does not require external pipelines and coolers, reducing pumping losses, thereby improving engine thermal efficiency, reducing fuel consumption, and achieving both emission reduction and energy saving. (ii) Achieving precise regulation through "dual NOx sensors + closed-loop control": The upstream NOx sensor of TWC monitors the raw emissions in real time, providing a basis for EGR rate adjustment. The downstream NOx sensor of SCR provides feedback on the conversion effect, and the ECU corrects the urea injection amount accordingly, which helps to improve SCR conversion efficiency and reduce urea consumption. At the same time, the downstream NOx sensor of SCR also provides data for the vehicle diagnostic system, which can diagnose EGR rate deviation and urea injection fault, avoiding vehicle torque limitation caused by excessive emissions. (iii) By increasing the exhaust temperature through internal EGR, when the DPF pressure difference exceeds the threshold and the SCR inlet temperature is >480℃, the ECU enhances the EGR rate to further increase the exhaust temperature, directly meeting the DPF active regeneration requirements without triggering HC injection. This method can cover most DPF regeneration scenarios, reduce the number of HC injections, extend the DOC lifespan, and avoid additional particulate matter generated by fuel combustion, reducing the risk of secondary pollution of DPF. (iv) The ECU pre-stores an EGR rate map based on speed-load. The EGR rate can be adjusted in real time within a certain range: a low EGR rate is used under low load to avoid combustion instability; it is initially increased under medium load to balance emissions and efficiency; and it is increased to the maximum value of the range under high load to suppress knocking and reduce NOx. This adaptive adjustment enables the engine to maintain optimal performance under different operating conditions, while the power output does not decrease, making it suitable for complex scenarios such as long-distance transportation and urban delivery. (v) By eliminating additional components through internal EGR, the structural compactness is improved and the overall vehicle layout space is reduced. It is especially suitable for the small engine compartment of commercial vehicles. The components of the aftertreatment unit are connected by short pipes and clamps, which makes disassembly and assembly convenient and shortens maintenance time. Furthermore, the DPF does not require frequent HC regeneration. The differential pressure sensor monitors the carbon load in real time, extending the regeneration cycle and reducing the average annual maintenance cost, thereby reducing operating expenses for logistics companies. (vi) Through the dual effect of “internal EGR reducing raw emissions + efficient conversion after treatment”, the final NOx emission concentration is ≤50mg / km and particulate matter emission is ≤3mg / km, which fully meets the existing emission standards. At the same time, the gas consumption rate is reduced and the amount of urea used is reduced, thereby reducing the carbon emissions of the whole vehicle throughout its life cycle, helping natural gas engines to upgrade from “low carbon” to “near zero carbon”, adapting to the “dual carbon” target of the transportation sector, and promoting the green transformation of the heavy commercial vehicle industry.

[0019] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] Figure 1 The present invention provides a logic block diagram of the exhaust gas recirculation thermal management system for a natural gas engine. Detailed Implementation

[0021] The embodiments of this utility model are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0022] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0023] This utility model provides an internal exhaust gas recirculation thermal management system for a natural gas engine. Its core lies in achieving precise control of internal exhaust gas recirculation (iEGR) through a fully variable hydraulic valve mechanism (FHVVS) and deep collaboration with the aftertreatment system, ultimately achieving a comprehensive effect of increasing exhaust temperature, reducing raw emissions, reducing urea consumption, and reducing pumping losses.

[0024] Specifically, see Figure 1 The exhaust gas recirculation thermal management system inside this natural gas engine mainly includes three functional units: Engine body and iEGR actuator: This unit is based on a high-horsepower natural gas engine. Its special feature is that it is equipped with a fully variable hydraulic valve mechanism (FHVVS). This mechanism replaces the traditional camshaft and can independently and continuously control the opening time, opening duration and maximum lift of the exhaust valve through the hydraulic control system. Aftertreatment unit: Along the exhaust flow direction of the engine, a three-way catalytic converter (TWC), a diesel oxidation catalyst (DOC), a particulate filter (DPF), and a selective catalytic reduction device (SCR) are arranged in series through pipelines. Urea nozzles are installed in front of the TWC and the SCR to inject urea water solution into the exhaust. Control and Sensing Unit: This unit is centered around the Electronic Control Unit (ECU), which receives signals from sensors throughout the system, including... Two NOx sensors: one located upstream of the TWC (for measuring raw NOx emissions from the engine) and the other downstream of the SCR (for providing closed-loop feedback signals to the SCR system and providing data to the OBD system). Three temperature sensors are located downstream of the TWC, upstream of the SCR, and downstream of the SCR, respectively, to monitor the operating temperature status of each catalyst. Differential pressure sensor: Installed on the DPF, it is used to measure the pressure difference before and after the DPF, thereby calculating its carbon loading; Based on this real-time data, the ECU drives the FHVVS mechanism and controls the urea injection system.

[0025] The exhaust outlet of the engine body is connected to the exhaust pipe via a flange. The exhaust pipe is connected in sequence to TWC, DOC, DPF and SCR. Each catalyst is connected to the other via a short pipe with a clamp. The entire aftertreatment unit is fixed to the vehicle frame or engine via a bracket.

[0026] The FHVVS mechanism is connected to the engine's hydraulic system through its own hydraulic control valve block, and its control signal harness is directly connected to the ECU's dedicated drive port.

[0027] All sensors (NOx sensor, temperature sensor, differential pressure sensor) are connected to the corresponding signal acquisition port of the ECU through their electrical interfaces. The urea nozzle is connected to the urea pump through the urea pipeline to form a urea injection system, which is controlled by the ECU to open and close.

[0028] The core working principle of this utility model is that the ECU intelligently drives the FHVVS mechanism to generate iEGR based on engine operating conditions and sensor feedback, and coordinates the work of the entire aftertreatment system. iEGR execution: The ECU has a pre-stored EGR rate MAP based on engine speed and load. Under target conditions such as medium load, the ECU sends a command to the FHVVS to open the exhaust valve for the second time in the late exhaust stroke or early intake stroke. By precisely controlling the phase and lift of this opening, a portion of the high-temperature exhaust gas that has already been discharged is reintroduced into the cylinder (or retained in the cylinder). This process achieves an EGR rate of 5%-35% and has an extremely fast response speed. By executing the iEGR above, the following effects can be achieved: Reduce raw emissions: Recirculated exhaust gas reduces the oxygen concentration and combustion temperature in the cylinder, effectively inhibiting NOx formation at the source; Increased exhaust temperature: The mixing of high-temperature exhaust gas and the adjustment of parameters such as ignition angle to maintain torque work together to significantly increase the exhaust gas temperature to TWC, which can reach more than 522℃ under medium load. Reduced pumping losses: Unlike the method of closing the throttle valve to generate negative pressure to introduce external EGR, iEGR is achieved directly through valve action, which greatly reduces pumping losses in the intake and exhaust process. Actual measurements show that it can reduce losses by more than 62.2%, thereby improving thermal efficiency and reducing fuel consumption rate. Collaboration with post-processing: For SCR systems: Due to the reduction in raw NOx emissions, the processing pressure on the SCR system is reduced. Based on feedback from the NOx sensor downstream of the SCR, the ECU can reduce the amount of urea injected while maintaining high conversion efficiency and avoiding ammonia leakage. For the DPF system: The exhaust temperature increased by iEGR first meets the temperature requirements for passive regeneration of DPF. When the differential pressure sensor detects that the carbon load of DPF is too high, the ECU's strategy is no longer to immediately trigger the traditional active HC injection regeneration, but to prioritize increasing the iEGR rate and try to further increase the exhaust temperature to the active regeneration window of 480°C or even 550°C. Only when iEGR alone cannot reach the required temperature will the backup plan (such as HC injection) be activated. This means that the system can eliminate or reduce the use of HC injectors between DOC and DPF, reducing system complexity and cost. Diagnosis and monitoring: The NOx sensor signal downstream of SCR is not only used for closed-loop control, but also input into the OBD system. By comprehensively analyzing the NOx concentration difference before TWC and after SCR, the ECU can intelligently diagnose multiple faults such as whether the iEGR rate is deviated or whether the urea injection system has failed.

[0029] Through the above specific implementation methods, this utility model utilizes FHVVS to achieve iEGR, eliminating the need for complex external EGR pipelines and coolers, resulting in a more compact structure and faster response. It achieves global optimized and coordinated control between the source engine and the end-of-line treatment, while simultaneously achieving multiple objectives such as reducing NOx, improving thermal efficiency, reducing urea consumption, and promoting DPF regeneration. It provides a cleaner and more efficient DPF regeneration method, reduces dependence on additional fuel injection, and achieves the goal of energy saving and emission reduction in high-horsepower natural gas engines.

[0030] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A natural gas engine internal exhaust gas recirculation thermal management system, characterized in that, include: The engine body is equipped with a variable hydraulic valve mechanism for generating internal exhaust gas recirculation by opening the exhaust valve a second time. The aftertreatment unit is arranged in series along the exhaust flow direction, including TWC, DOC, DPF and SCR, and urea nozzles are provided upstream of TWC and SCR. The control unit is used to drive the variable hydraulic valve mechanism to perform secondary opening of the exhaust valve under medium load conditions, so as to reintroduce some exhaust gas into the cylinder, increase the exhaust temperature and reduce the original NOx emissions.

2. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, NOx sensors are installed upstream of the TWC and downstream of the SCR. The former sensor is used to measure the engine's original NOx emissions, while the latter sensor provides a closed-loop signal to the SCR for closed-loop correction of urea injection quantity.

3. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 2, characterized in that, The NOx sensor downstream of the SCR inputs a signal to the on-board diagnostic system for dual diagnosis of EGR rate deviation and urea injection deviation.

4. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, The control unit is set with an EGR rate map, and the EGR rate is controlled within the range of 5% to 35%, and is adjusted in real time according to the speed and load.

5. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, When the DPF differential pressure is greater than the set threshold and the SCR inlet temperature is greater than 480°C, the control unit uses internal EGR heating and regeneration.

6. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, The variable hydraulic valve mechanism is an FHVVS fully variable hydraulic valve mechanism, which can achieve stepless adjustment of the exhaust valve's secondary opening lift and phase within the same cycle.

7. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, There is no HC injector between the DOC and DPF; the exhaust temperature is met by the internal EGR alone.

8. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, The DPF is equipped with a differential pressure sensor to measure the airflow resistance of the DPF.

9. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, Temperature sensors are installed downstream of the TWC and upstream and downstream of the SCR. The urea injection system calculates the required urea injection amount based on the temperature of the TWC and SCR catalysts.

10. The exhaust gas recirculation thermal management system for a natural gas engine according to claim 1, characterized in that, The control unit is an on-board ECU.

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