A natural gas engine EGR control system

Abstract

The application relates to a natural gas engine EGR control system, which comprises an engine air inlet pipeline, an EGR mixing pipeline, an engine exhaust pipeline and a waste gas recovery pipeline, the engine air inlet pipeline is provided with a throttle valve and an engine body arranged in sequence along the gas flow direction; the EGR mixing pipeline is communicated with the engine air inlet pipeline and is used for mixing air and waste gas to be sent to the engine air inlet pipeline; the engine exhaust pipeline is provided with a turbine; the waste gas recovery pipeline is connected with the EGR mixing pipeline and the engine exhaust pipeline, the waste gas recovery pipeline is provided with a high-pressure EGR valve and a low-pressure EGR valve; and when the high-pressure EGR valve is opened, the waste gas recovery pipeline sends the waste gas before being treated by the turbine to the EGR mixing pipeline; when the low-pressure EGR valve is opened, the waste gas recovery pipeline sends the waste gas after being treated by the turbine to the EGR mixing pipeline. In the application, the throttle valve controls the fresh air intake, the high-pressure EGR valve and the low-pressure EGR valve can inhibit the engine body knock and explosion pressure, and the economy of the engine body is improved.

Description

Technical Field

[0001] This application relates to the field of natural gas engines, and in particular to an EGR control system for a natural gas engine. Background Technology

[0002] The principle of EGR (Exhaust Gas Recirculation) is to reintroduce cooled recirculated exhaust gas into the combustion chamber, reducing the effective air-fuel ratio while having little impact on the thermal load. Its main purpose is to reduce NOx emissions from diesel engines through combustion optimization and to reduce knocking and detonation in natural gas. This is achieved by introducing exhaust gas from the exhaust pipe into the intake manifold, thereby reducing the intake oxygen concentration. Existing EGR systems are controlled separately from other components of the air system, especially the throttle valve. Natural gas engines use quantity regulation, meaning the amount of air-fuel mixture (e.g., a mixture of natural gas and air) is controlled by the throttle valve to change the engine load. The engine load is directly controlled by the throttle valve; that is, under low engine load conditions, the throttle opening is smaller to control the amount of fresh air intake. This smaller intake air volume, combined with a smaller natural gas supply, achieves power and torque under low load conditions, while simultaneously working with the EGR system to control knocking in natural gas engines. However, in the above technologies, due to the smaller throttle opening, the intake throttling loss is significant, which is detrimental to engine economy. Summary of the Invention

[0003] This application provides an EGR control system for a natural gas engine to solve the problem in related technologies where the throttle opening is small and the intake throttling loss is large under low-load conditions, which is detrimental to the engine's economy.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a natural gas engine EGR control system, comprising: an engine intake pipe, an EGR mixing pipe, an engine exhaust pipe, and an exhaust gas recovery pipe; wherein the engine intake pipe is provided with a throttle valve and an engine body arranged sequentially along the gas flow direction; the EGR mixing pipe is connected to the engine intake pipe and is used to mix air with exhaust gas for delivery to the engine intake pipe; a turbine is provided on the engine exhaust pipe; the exhaust gas recovery pipe is connected to the EGR mixing pipe and the engine exhaust pipe, and is provided with a high-pressure EGR valve and a low-pressure EGR valve; and wherein, when the high-pressure EGR valve is open, the exhaust gas recovery pipe delivers exhaust gas before it has been treated by the turbine to the EGR mixing pipe; and when the low-pressure EGR valve is open, the exhaust gas recovery pipe delivers exhaust gas after it has been treated by the turbine to the EGR mixing pipe.

[0005] In some embodiments, the engine exhaust pipe is also equipped with an aftertreatment system. The turbine and the aftertreatment system are arranged sequentially along the gas flow direction. When the low-pressure EGR valve is opened, the exhaust gas recovery pipe sends the exhaust gas treated by the aftertreatment system to the EGR mixing pipe.

[0006] In some embodiments, the EGR control system further includes an intercooler assembly, wherein the exhaust gas recovery line is connected to the EGR mixing line via the intercooler assembly, and the EGR mixing line is connected to the engine intake line via the intercooler assembly.

[0007] In some embodiments, the intercooler assembly includes an air-to-air intercooler, and both the exhaust gas recovery line and the EGR mixing line pass through the air-to-air intercooler.

[0008] In some embodiments, the exhaust gas recovery pipeline is also equipped with an EGR cooler; when the high-pressure EGR valve is open, the exhaust gas recovery pipeline sends the exhaust gas before it is treated by the turbine to the EGR mixing pipeline after being treated by the EGR cooler; when the low-pressure EGR valve is open, the exhaust gas recovery pipeline sends the exhaust gas after it is treated by the turbine to the EGR mixing pipeline after being treated by the EGR cooler.

[0009] In some embodiments, the engine exhaust pipe includes a first branch and a second branch, the first branch being connected to the engine body and the turbine, and the second branch being connected to the engine body and the turbine, so that the exhaust gas discharged from the engine body is divided into two paths, which are respectively sent to the turbine for processing via the first branch and the second branch.

[0010] In some embodiments, the high-pressure EGR valve includes a first high-pressure EGR valve and a second high-pressure EGR valve. The third branch containing the first high-pressure EGR valve is connected to the first branch and the EGR cooler, and the fourth branch containing the second high-pressure EGR valve is connected to the second branch and the EGR cooler. When the first high-pressure EGR valve is open, the exhaust gas discharged from the engine body is sent to the EGR cooler for processing along the first and third branches. When the second high-pressure EGR valve is closed, the exhaust gas discharged from the engine body is sent to the EGR cooler for processing along the second and fourth branches.

[0011] In some embodiments, the waste gas recovery pipeline is also equipped with a water separator.

[0012] In some embodiments, the EGR mixing line is provided with an EGR mixer and a compressor arranged sequentially along the gas flow direction. The EGR mixer is used to mix air with exhaust gas and send it to the compressor. The compressor is used to compress the air and exhaust gas and send it to the engine intake line.

[0013] In some embodiments, a natural gas injector is also provided on the engine intake manifold, and the throttle valve, the natural gas injector, and the engine body are arranged sequentially along the gas flow direction.

[0014] The beneficial effects of the technical solution provided in this application include:

[0015] This application provides an EGR control system for a natural gas engine. It utilizes the throttle valve to control the amount of fresh air intake (i.e., to ensure the engine operates at low load). A high-pressure EGR valve and a low-pressure EGR valve work together in this system. The low-pressure EGR valve supplements the EGR flow, preventing excessive gas flow to the high-pressure EGR valve when it is opened too wide. This ensures sufficient EGR flow to the EGR mixing line while reducing the impact of the exhaust gas recovery line on the turbine's work. It also suppresses engine knock and pressure build-up, reduces throttling losses, and improves the engine's fuel economy. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A system schematic diagram of a single-suction high-pressure EGR valve provided in an embodiment of this application;

[0018] Figure 2 This is a system schematic diagram of a dual-suction high-pressure EGR valve provided in an embodiment of this application;

[0019] Figure 3 Pressure fluctuation diagram of dual-path EGR gas sampling provided in the embodiments of this application;

[0020] Figure 4 A schematic diagram of the control method provided in the embodiments of this application.

[0021] In the diagram: 1. EGR mixing line; 10. EGR mixer; 11. Compressor;

[0022] 2. Engine intake manifold; 20. Throttle valve; 21. Natural gas injector; 22. Engine block;

[0023] 3. Engine exhaust pipe; 30. Turbine; 31. Aftertreatment system; 32. First branch; 33. Second branch;

[0024] 4. Exhaust gas recovery pipeline; 40. High-pressure EGR valve; 400. First high-pressure EGR valve; 401. Second high-pressure EGR valve; 41. Low-pressure EGR valve; 42. EGR cooler; 43. Water separator;

[0025] 5. Air ductwork;

[0026] 6. Air-to-air intercooler. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] See Figures 1 to 4 This application provides an EGR control system for a natural gas engine, which can solve the problem in related technologies that the throttle opening is small and the intake throttling loss is large when the engine is under low load, which is not conducive to the engine's economy.

[0029] The principle of EGR (Exhaust Gas Recirculation) is to reintroduce cooled, recirculated exhaust gas into the combustion chamber, reducing the effective air-fuel ratio while having minimal impact on the heat load. Its main purpose is to reduce NOx emissions from diesel engines through combustion optimization. This is achieved by introducing exhaust gas from the engine exhaust pipe into the engine intake manifold, thereby reducing the intake oxygen concentration. The main reason EGR reduces NOx emissions is:

[0030] 1. Thermal effect: CO2 and H2O in the exhaust gas can increase the specific heat capacity of the in-cylinder charge of the engine, thereby reducing the combustion temperature;

[0031] 2. Dilution effect: The introduction of exhaust gas reduces the O2 concentration in the engine cylinder. The reduced oxide concentration and decreased activity lead to a decrease in the combustion reaction rate.

[0032] 3. Chemical effects: CO2 and H2O in the exhaust gas undergo dissociation reactions after entering the engine cylinder, thereby changing the combustion process and NOx generation. In particular, the endothermic decomposition reaction of water vapor directly reduces the combustion flame temperature.

[0033] In existing technologies, the EGR system is controlled separately from other components of the air system, especially the throttle valve 20. Natural gas engines use quantity regulation, where the engine load is directly controlled by the throttle valve 20. That is, under low engine load conditions, the throttle valve 20 opening is smaller to control the amount of fresh air intake. This smaller intake air volume, combined with a smaller natural gas supply, achieves power and torque under low load conditions. Simultaneously, it works with the EGR system to control knocking in the natural gas engine. However, in the above technology, due to the smaller throttle valve 20 opening, the intake throttling loss is significant, which is detrimental to engine economy.

[0034] To address the issue that the throttle opening is small and intake throttling losses are large when the engine is under low load, which is detrimental to engine economy, this paper proposes a new technology. This application provides an EGR control system for a natural gas engine, comprising: an engine intake pipe 2, an EGR mixing pipe 1, an engine exhaust pipe 3, and an exhaust gas recovery pipe 4. The engine intake pipe 2 is provided with a throttle valve 20 and an engine body 22 arranged sequentially along the gas flow direction. The EGR mixing pipe 1 is connected to the engine intake pipe 2 and is used to mix air with exhaust gas for delivery to the engine intake pipe 2. The engine exhaust pipe 3 is provided with a turbine 30. The exhaust gas recovery pipe 4 is connected to the EGR mixing pipe 1 and the engine exhaust pipe 3, and is provided with a high-pressure EGR valve 40 and a low-pressure EGR valve 41. When the high-pressure EGR valve 40 is open, the exhaust gas recovery pipe 4 delivers the exhaust gas before it is processed by the turbine 30 to the EGR mixing pipe 1. When the low-pressure EGR valve 41 is open, the exhaust gas recovery pipe 4 delivers the exhaust gas after it is processed by the turbine 30 to the EGR mixing pipe 1.

[0035] It should be noted that the gas flow direction mentioned in this application refers to the direction in which gas flows from the exhaust port of the engine body 22 to the air intake port of the engine body 22.

[0036] In this application, the throttle valve 20 is used to control the amount of fresh air intake (i.e., to make the engine body 22 operate at low load). A high-pressure EGR valve 40 and a low-pressure EGR valve 41 are set up to work together. The low-pressure EGR valve 41 supplements the EGR flow, avoiding the large amount of gas flowing to the high-pressure EGR valve 40 when the high-pressure EGR valve 40 is opened too large when the high-pressure EGR valve 40 is used alone. While ensuring that the sufficient EGR flow to the EGR mixing pipeline 1 is met, the impact of the exhaust gas recovery pipeline 4 on the work of the turbine 30 is reduced. It can also suppress knocking and depressurization of the engine body 22, reduce throttling losses, and improve the economy of the engine body 22.

[0037] The engine intake manifold 2 is also equipped with a natural gas injector 21. Along the gas flow direction, the throttle valve 20, the natural gas injector 21, and the engine body 22 are arranged in sequence. Therefore, the EGR gas enters the EGR mixing manifold 1 and mixes with fresh air, and then enters the engine intake manifold 2. The opening of the throttle valve 20 is used to control the load on the engine body 22. After the mixed gas passes through the throttle valve 20, it mixes with the natural gas injected by the natural gas injector 21, and finally enters the engine body 22 for combustion and power generation. Part of the exhaust gas generated by the combustion in the engine body 22 passes through the engine exhaust manifold 3 to drive the turbine 30 to do power and is then discharged. The other part of the exhaust gas is recirculated into the EGR mixing manifold 1 through the exhaust gas recovery manifold 4.

[0038] Since the engine exhaust pipe 3 is equipped with a turbine 30, the turbine 30 divides the engine exhaust pipe 3 into a front section and a rear section: the exhaust gas from the combustion of the engine body 22 passes through the front section, drives the turbine 30 to do work, and is then discharged from the rear section.

[0039] The exhaust gas recovery pipeline 4 includes a high-pressure branch and a low-pressure branch. A high-pressure EGR valve 40 is installed on the high-pressure branch, and a low-pressure EGR valve 41 is installed on the low-pressure branch. The high-pressure branch is connected to the upstream EGR mixing pipeline 1, and the low-pressure branch is connected to the downstream EGR mixing pipeline 1.

[0040] If only the high-pressure EGR valve 40 is installed, when the opening of the high-pressure EGR valve 40 is small, there is a risk that the exhaust gas flow from the exhaust gas recovery pipeline 4 to the EGR mixing pipeline 1 will be insufficient, making it difficult to suppress knocking and pressure explosion in the engine body 22. When the opening of the high-pressure EGR valve 40 is large, the exhaust gas flow driving the turbine 30 to do work will decrease, which will affect the work done by the turbine 30 and thus affect the fuel consumption of the engine body 22. After setting up a low-pressure branch connected to the downstream section, when the low-pressure EGR valve 41 is open, it can send the exhaust gas treated by the turbine 30 to the EGR mixing pipeline 1. At this time, it is not necessary to adjust the opening of the high-pressure EGR valve 40 too large, and sufficient EGR flow (exhaust gas flow) can be met to flow to the EGR mixing pipeline 1.

[0041] Based on the above embodiments, in this embodiment, the engine exhaust pipe 3 is also provided with an aftertreatment system 31. The turbine 30 and the aftertreatment system 31 are arranged sequentially along the gas flow direction. When the low-pressure EGR valve 41 is opened, the exhaust gas recovery pipe 4 sends the exhaust gas treated by the aftertreatment system 31 to the EGR mixing pipe 1.

[0042] In this embodiment, a turbine 30 and an aftertreatment system 31 are installed on the engine intake pipe 2 so that the exhaust gas enters the aftertreatment system 31 after passing through the turbine 30 to reduce the content of corrosive substances in the exhaust gas. At this time, the turbine 30 and the aftertreatment system 31 divide the engine intake pipe 2 into a front section, a middle section and a rear section. The high-pressure branch is connected to the front section and the EGR mixing pipe 1, and the low-pressure branch is connected to the rear section and the EGR mixing pipe 1. At this time, the exhaust gas passing through the rear section is the gas after being treated by the aftertreatment system 31.

[0043] The EGR mixing line 1 is provided with an EGR mixer 10 and a compressor 11 arranged sequentially along the gas flow direction. The EGR mixer 10 is used to mix air and exhaust gas and send it to the compressor 11. The compressor 11 is used to compress air and exhaust gas and send it to the engine intake line 2.

[0044] The EGR mixer 10 includes two air inlets. One air inlet is connected to an air pipe 5 to inject fresh air into the EGR mixer 10, and the other air inlet is connected to an exhaust gas recovery pipe 4 to inject exhaust gas into the EGR mixer 10. The fresh air and exhaust gas are evenly mixed in the EGR mixer 10, sent to the compressor 11 for compression, and then enter the cylinder of the engine body 22 to participate in the combustion process, so as to increase the exhaust gas charge, increase the air density, increase the intake volume, and reduce knocking and detonation.

[0045] Based on the above embodiments, in this implementation, the EGR control system further includes: an intercooler assembly, the exhaust gas recovery pipeline 4 is connected to the EGR mixing pipeline 1 through the intercooler assembly, and the EGR mixing pipeline 1 is connected to the engine intake pipeline 2 through the intercooler assembly.

[0046] The energy of the exhaust gas discharged from the engine block 22 drives the compressor 11 to pump air into the intake manifold of the engine block 22, thereby increasing the density and pressure of the intake air and making the fuel combustion more complete. However, the pressurized gas will be very hot due to the high temperature of the compressor 11, which will significantly affect the boosting effect. Therefore, in order to further improve the boosting efficiency and improve the boosting technology, the gas pressurized by the compressor 11 is sent to the intercooler assembly for cooling, thereby increasing the intake air density.

[0047] In this embodiment, a multi-stage cooling method is used to cool the gas. Specifically, the intercooler assembly includes an air-to-air intercooler 6, and both the exhaust gas recovery pipeline 4 and the EGR mixing pipeline 1 pass through the air-to-air intercooler 6.

[0048] The exhaust gas entering the exhaust gas recovery line 4 passes through the air-to-air intercooler 6 and then enters the EGR mixer 10 for mixing. The mixed gas then passes through the compressor 11, and is cooled again by the air-to-air intercooler 6 before being sent to the engine block 22. By using an air-to-air intercooler 6 to cool both the exhaust gas entering the EGR mixing line 1 and the exhaust gas entering the engine intake line 2, the system layout becomes more compact, reducing its overall size.

[0049] Based on the above embodiments, in this embodiment, in order to further reduce the temperature of the exhaust gas entering the EGR mixing pipeline 1, the exhaust gas recovery pipeline 4 is also equipped with an EGR cooler 42; when the high-pressure EGR valve 40 is opened, the exhaust gas recovery pipeline 4 sends the exhaust gas before it is processed by the turbine 30 to the EGR mixing pipeline 1 after being processed by the EGR cooler 42; when the low-pressure EGR valve 41 is opened, the exhaust gas recovery pipeline 4 sends the exhaust gas after it is processed by the turbine 30 to the EGR mixing pipeline 1 after being processed by the EGR cooler 42.

[0050] Specifically, the high-pressure branch and the low-pressure branch are connected to the EGR cooler 42: When the high-pressure EGR valve 40 is open, the high-pressure branch draws gas before the turbine 30 (front section), and the exhaust gas passes through the high-pressure branch into the EGR cooler 42 for cooling, then enters the air-to-air intercooler 6 for further cooling, and finally enters the EGR mixer 10; when the low-pressure EGR valve 41 is open, the low-pressure branch draws gas after the aftertreatment system 31 (rear section), and the exhaust gas passes through the low-pressure branch into the EGR cooler 42 for cooling, then enters the air-to-air intercooler 6 for further cooling, and finally enters the EGR mixer 10. Furthermore, the exhaust gas from the low-pressure branch and the exhaust gas from the high-pressure branch are mixed after passing through the EGR cooler 42 and then enter the air-to-air intercooler 6 together.

[0051] The exhaust gas is controlled by adjusting the opening of the high-pressure EGR valve 40 and the low-pressure EGR valve 41 to control the EGR rate (exhaust gas rate), i.e., the exhaust gas flow rate. The exhaust gas is initially cooled by the EGR cooler 42. In this embodiment, at the rated point of the engine body 22 (the operating condition at which the engine body 22 can achieve the maximum power), the gas temperature at the outlet of the EGR cooler 42 is approximately 130°C. After the exhaust gas enters the air-to-air intercooler 6 for secondary cooling, the gas temperature at the outlet of the air-to-air intercooler 6 is approximately 45°C.

[0052] In this embodiment, as Figure 1 As shown, the high-pressure branch has a single gas intake, and the EGR cooler 42 is an integrated dual-channel cooler (one channel is connected to the high-pressure branch, and the other channel is connected to the low-pressure branch).

[0053] In other embodiments, such as Figure 2As shown, the high-pressure branch has dual gas intake, including a third branch and a fourth branch. The EGR cooler 42 is an integrated three-channel cooler (one channel is connected to the third branch, one channel is connected to the fourth branch, and one channel is connected to the low-pressure branch) in order to retain pulse energy to the maximum extent.

[0054] Specifically, the engine exhaust pipe 3 includes a first branch 32 and a second branch 33. The first branch 32 is connected to the engine intake pipe 2 and the turbine 30, and the second branch 33 is connected to the engine intake pipe 2 and the turbine 30, so that the exhaust gas discharged from the engine intake pipe 2 is divided into two paths, which are respectively sent to the turbine 30 for processing via the first branch 32 and the second branch 33.

[0055] The high-pressure EGR valve 40 includes a first high-pressure EGR valve 400 and a second high-pressure EGR valve 401. The third branch containing the first high-pressure EGR valve 400 is connected to the first branch 32 and the EGR cooler 42. The fourth branch containing the second high-pressure EGR valve 401 is connected to the second branch 33 and the EGR cooler 42. When the first high-pressure EGR valve 400 is open, the exhaust gas discharged from the engine intake pipe 2 is sent to the EGR cooler 42 for processing along the first branch 32 and the third branch. When the second high-pressure EGR valve 401 is open, the exhaust gas discharged from the engine intake pipe 2 is sent to the EGR cooler 42 for processing along the second branch 33 and the fourth branch.

[0056] In this embodiment, the engine body 22 is configured as a six-cylinder engine. Figure 2 The engine block 22, from left to right, has cylinders 1, 2, 3, 4, 5, and 6. The first branch line 32 draws air from cylinders 1, 2, and 3 of the engine block 22, and the second branch line 33 draws air from cylinders 4, 5, and 6 of the engine block 22. Due to the firing order of the engine block 22, taking a six-cylinder engine as an example, its firing order is cylinders 1, 5, 3, 6, 2, and 4. Figure 3 As shown, the exhaust pulse pressure fluctuation shape will correspond to 6 peaks for each firing cylinder.

[0057] If a dual intake method is used, the charge at the peak can be maintained continuously. The higher peak pressure brings in more gas, resulting in a higher EGR (exhaust gas regeneration rate). The gas from the third and fourth branches can maintain a higher pressure without being affected (the intake of cylinders 1, 2, and 3 on the left side is not affected by cylinders 4, 5, and 6 on the right side; the intake of cylinders 4, 5, and 6 on the right side is not affected by cylinders 1, 2, and 3 on the left side). For example, the left three cylinders can maintain a maximum pressure of 5.5 bar, and the right three cylinders can maintain a maximum pressure of 5.5 bar.

[0058] Conversely, if a single air intake method is used, the peaks and troughs overlap and influence each other, lowering the peaks and filling the troughs, thus reducing exhaust gas. Specifically, if a single air intake is used, the pressures of the left three cylinders and the right three cylinders affect each other. The maximum pressure of the gas in the third and fourth branches is less than 5.5 bar. After the pressure in the third and fourth branches is averaged, the pressure range is 4–4.5 bar. Compared to the maximum pressure of 5.5 bar, this pressure is 1–1.5 bar less, resulting in a 1–1.5 bar reduction in gas driving capacity.

[0059] Because the gas intake capacity of the third and fourth branches is related to the pressure difference (i.e., the pressure at the inlet of the third and fourth branches must be greater than the pressure at the inlet of the EGR mixing line 1): when there is a pressure difference, the third and fourth branches can take in gas, and the gas in the exhaust gas recovery line 4 can flow into the EGR mixer 10; when there is no pressure difference, the third and fourth branches cannot take in gas, and the gas in the exhaust gas recovery line 4 does not flow into the EGR mixer 10. Therefore, the dual-intake method can obtain more exhaust gas.

[0060] Based on the above embodiments, in this embodiment, the exhaust gas recovery pipeline 4 is further equipped with a water separator 43. The exhaust gas from the exhaust gas recovery pipeline 4, after passing through the air-to-air intercooler 6, enters the water separator 43 to remove water, and then enters the EGR mixer 10. The water separator 43 removes water from the exhaust gas, protecting the downstream compressor 11 blades from moisture corrosion. Simultaneously, since the CH4 component of natural gas readily reacts with the oxygen (O2) component in the air to generate water that enters the cylinders of the engine block 22, especially depositing in the first cylinder through which the gas passes, this can lead to uneven intake airflow in each cylinder. This results in significant differences in exhaust temperature at the outlets of the cylinders of the engine block 22 before the turbine 30, affecting reliability and impacting engine knocking and fuel economy. Therefore, the addition of the water separator 43 can mitigate these problems.

[0061] The following table compares the high-load and low-load operating conditions of the prior art with those of this application:

[0062]

[0063]

[0064] In this application, the throttle valve 20 opening is slightly increased, and the opening of the EGR valves (high-pressure EGR valve 40 and low-pressure EGR valve 41) is also increased. Through the cooperation of the throttle valve 20 and the EGR valves, the intake air volume is reduced under low-load conditions: the EGR valve controls the EGR flow rate, and the throttle valve 20 controls the intake air volume. The EGR valve and throttle valve 20 work together to reduce throttling losses under low-load conditions, thus improving the fuel economy of the engine 22. The specific values ​​of the throttle valve 20 and EGR valve openings are determined through calibration.

[0065] Control of high-pressure EGR valve 40 and low-pressure EGR valve 41: The opening of high-pressure EGR valve 40 needs to be calibrated to achieve optimal economy. During calibration, several combinations can achieve the same EGR rate: for example, high-pressure EGR valve 40 opening 80% + low-pressure EGR valve 41 opening 20% ​​= 200 kg / h EGR flow; high-pressure EGR valve 40 opening 40% + low-pressure EGR valve 41 opening 50% = 200 kg / h EGR flow. Although both opening adjustment methods can achieve the same EGR flow, both can control engine knock within limits. However, using the high-pressure EGR valve 40 reduces the pumping loss of the engine block 22 (a benefit; pumping loss can be characterized by the pressure value before the turbine 30; higher pressure results in greater pumping loss; with greater pumping loss, the engine block 22 consumes more power for pumping, thus reducing its effective power and increasing fuel consumption). Simultaneously, the reduced exhaust gas flow to the turbine 30 leads to decreased turbine efficiency (a drawback). Therefore, it is necessary to find the optimal combination of the opening degrees of the high-pressure EGR valve 40 and the low-pressure EGR valve 41, requiring calibration of both. The calibration aims to achieve the optimal specific gas consumption while maintaining the knock limit as a boundary. In this application, the calibration is performed manually.

[0066] The calibration method is as follows:

[0067] 101: Based on the initial value of throttle valve opening 20, scan the opening of high-pressure EGR valve 40 and low-pressure EGR valve 41 under this opening condition, and select the economically optimal operating condition under the knock limit from the permutation and combination results of high-pressure EGR valve 40 opening and low-pressure EGR valve 41 opening based on the same EGR flow.

[0068] 102: Increase the throttle valve opening by 20. Under this opening condition, scan the opening of the high-pressure EGR valve 40 and the low-pressure EGR valve 41. Based on the same EGR flow, select the economically optimal operating condition under the knock limit from the permutation and combination results of the high-pressure EGR valve 40 opening and the low-pressure EGR valve 41 opening.

[0069] 103: Until the knocking exceeds the limit, no operating condition is within the knocking limit. Then determine the maximum value of the throttle valve 20 opening before the knocking exceeds the limit, and determine the final opening of the high-pressure EGR valve 40 and the low-pressure EGR valve 41 based on the economically optimal operating condition corresponding to the maximum value.

[0070] By determining the final opening degrees of the high-pressure EGR valve 40, the low-pressure EGR valve 41, and the throttle valve 20, the engine body 22 achieves optimal specific gas consumption and optimal economy.

[0071] like Figure 4 As shown, Figure 4 In the diagram, A1 represents the basic value of throttle valve opening at 20°, and B1 represents the limit value of throttle valve opening at 20°; A2 represents the basic value of high-pressure EGR valve opening at 40°, and B2 represents the limit value of high-pressure EGR valve opening at 40°; A3 represents the basic value of low-pressure EGR valve opening at 41°, and B3 represents the limit value of low-pressure EGR valve opening at 41°.

[0072] The ECU (Electronic Control Unit) in a car senses the speed and fuel levels through sensors, thus determining the engine's RPM and fuel consumption, and consequently, the engine's operating condition. Under the corresponding operating conditions of the engine's RPM and fuel consumption, it's necessary to determine the throttle opening 20, the high-pressure EGR valve 40, and the low-pressure EGR valve 41. Therefore, a baseline value is first assigned to each of these values: taking the throttle opening 20 as an example, based on this baseline value, the PID controller 1 stabilizes the throttle opening value (within the throttle opening limit range). Then, the current throttle opening value is output, and combined with the current high-pressure EGR valve 40 and low-pressure EGR valve 41 openings, the ECU obtains the engine's fuel consumption and knock / detonation status. The experimental data is then retained. Adjusting the throttle valve 20 opening to increase or decrease its value, along with the opening of the high-pressure EGR valve 40 and the low-pressure EGR valve 41, will yield new fuel consumption and knock pressure / knock conditions for the engine body 22. Repeating the steps of retaining experimental data and adjusting the throttle valve 20 opening, and selecting the optimal combination from the permutations of the throttle valve 20 opening, the high-pressure EGR valve 40 opening, and the low-pressure EGR valve 41 opening, represents the most economical operating condition under the same EGR flow rate and knock limit.

[0073] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0074] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0075] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A natural gas engine EGR control system, characterized in that, It includes: Engine intake pipe (2), the engine intake pipe (2) is provided with a throttle valve (20) and an engine body (22) arranged sequentially along the gas flow direction. EGR mixing line (1), which is connected to the engine intake line (2) and is used to mix air with exhaust gas to deliver it to the engine intake line (2). Engine exhaust pipe (3), on which a turbine (30) is provided; Exhaust gas recovery pipeline (4), the exhaust gas recovery pipeline (4) is connected to EGR mixing pipeline (1) and engine exhaust pipeline (3), and the exhaust gas recovery pipeline (4) is equipped with high pressure EGR valve (40) and low pressure EGR valve (41). And, when the high-pressure EGR valve (40) is opened, the exhaust gas recovery line (4) sends the exhaust gas before it is treated by the turbine (30) to the EGR mixing line (1). When the low-pressure EGR valve (41) is opened, the exhaust gas recovery pipeline (4) sends the exhaust gas treated by the turbine (30) to the EGR mixing pipeline (1). The EGR control system also includes: Intercooler assembly, the exhaust gas recovery pipeline (4) is connected to the EGR mixing pipeline (1) through the intercooler assembly, and the EGR mixing pipeline (1) is connected to the engine intake pipeline (2) through the intercooler assembly; The intercooler assembly includes an air-to-air intercooler (6), and the exhaust gas recovery pipeline (4) and the EGR mixing pipeline (1) both pass through the air-to-air intercooler (6). The EGR mixing pipeline (1) is provided with an EGR mixer (10) and a compressor (11) arranged sequentially along the gas flow direction. The EGR mixer (10) is used to mix air and exhaust gas to send to the compressor (11). The compressor (11) is used to compress air and exhaust gas to send to the engine intake pipeline (2). The engine intake pipe (2) is also equipped with a natural gas injector (21). Along the gas flow direction, the throttle valve (20), the natural gas injector (21) and the engine body (22) are arranged in sequence.

2. The natural gas engine EGR control system as described in claim 1, characterized in that: The engine exhaust pipe (3) is also equipped with an aftertreatment system (31). The turbine (30) and the aftertreatment system (31) are arranged in sequence along the gas flow direction. When the low-pressure EGR valve (41) is opened, the exhaust gas recovery pipe (4) sends the exhaust gas treated by the aftertreatment system (31) to the EGR mixing pipe (1).

3. The natural gas engine EGR control system as described in claim 1, characterized in that, The waste gas recovery pipeline (4) is also equipped with an EGR cooler (42). When the high-pressure EGR valve (40) is opened, the exhaust gas recovery pipeline (4) sends the exhaust gas before it is processed by the turbine (30) to the EGR mixing pipeline (1) after being processed by the EGR cooler (42). When the low-pressure EGR valve (41) is opened, the exhaust gas recovery pipeline (4) sends the exhaust gas treated by the turbine (30) to the EGR mixing pipeline (1) after being treated by the EGR cooler (42).

4. The natural gas engine EGR control system as described in claim 3, characterized in that: The engine exhaust pipe (3) includes a first branch (32) and a second branch (33). The first branch (32) is connected to the engine body (22) and the turbine (30), and the second branch (33) is connected to the engine body (22) and the turbine (30), so that the exhaust gas discharged from the engine body (22) is divided into two paths and sent to the turbine (30) for processing via the first branch (32) and the second branch (33) respectively.

5. The natural gas engine EGR control system as described in claim 4, characterized in that: The high-pressure EGR valve (40) includes a first high-pressure EGR valve (400) and a second high-pressure EGR valve (401). The third branch where the first high-pressure EGR valve (400) is located is connected to the first branch (32) and the EGR cooler (42). The fourth branch where the second high-pressure EGR valve (401) is located is connected to the second branch (33) and the EGR cooler (42). When the first high-pressure EGR valve (400) is opened, the exhaust gas discharged from the engine body (22) is sent to the EGR cooler (42) for processing along the first branch (32) and the third branch; When the second high-pressure EGR valve (401) is closed, the exhaust gas discharged from the engine body (22) is sent to the EGR cooler (42) for processing along the second branch (33) and the fourth branch.

6. The natural gas engine EGR control system as described in claim 1, characterized in that: The waste gas recovery pipeline (4) is also equipped with a water separator (43).

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