A method for predicting in-cylinder swirl angle momentum of a marine low-speed engine during a scavenging process and a prediction system thereof
By using the improved Sigmoid function and the principle of conservation of angular momentum, the in-cylinder vortex angular momentum loss is calculated, solving the problem of rapid and accurate prediction of the in-cylinder vortex level in marine low-speed engines, thereby improving combustion efficiency and reducing emissions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN ENG UNIV
- Filing Date
- 2023-06-20
- Publication Date
- 2026-07-21
AI Technical Summary
Existing technologies make it difficult to quickly and accurately predict the in-cylinder swirl level in the two-stroke DC scavenging structure of marine low-speed engines, resulting in poor fuel-air mixture formation and affecting combustion efficiency and emissions.
A modified Sigmoid function is used to simulate the in-cylinder vortex velocity field. Combined with the principle of conservation of angular momentum, the vortex angular momentum loss, including mass loss, wall friction and internal shear loss, is calculated, and a vortex angular momentum prediction model is established.
It enables rapid and accurate prediction of the angular momentum of the in-cylinder vortex in marine low-speed engines, providing initial boundary conditions for spray combustion in low-speed engines, improving combustion efficiency and reducing emissions.
Smart Images
Figure CN116756972B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of power energy technology, specifically relating to a method and system for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine. Background Technology
[0002] With the rapid development of the global shipping industry, the power, economy, and reliability of marine engines have become a focus for ship manufacturers and users. Currently, low fuel consumption and low emissions remain the fundamental goals of marine engine development. In marine two-stroke direct-current scavenging engine systems, the extremely long scavenging process increases the complexity of the gas state and flow within the cylinder. The level of in-cylinder swirl directly affects the formation of the fuel-air mixture, thereby impacting combustion efficiency and emissions. Therefore, it is necessary to study the swirl level during the in-cylinder scavenging process.
[0003] Due to the large size and high cost of testing marine low-speed engines, domestic and international experts and scholars currently rely heavily on numerical simulations for research, including computational fluid dynamics (CFD) models (multidimensional models) and phenomenological models (zero-dimensional and quasi-dimensional models). CFD simulations primarily simulate and predict the in-cylinder airflow temperature, pressure, velocity, and mass fields under different structural parameters and scavenging strategies, thereby evaluating the scavenging effect. However, CFD models are time-consuming and difficult to rapidly parameterize. Phenomenological models, on the other hand, are increasingly important in engine simulation due to their advantages such as detailed descriptions of physical processes, faster computation speed, and the ability to be combined with data-driven models to form real-time gray box models. Currently, most phenomenological model studies on airflow motion levels during the scavenging process by domestic and international scholars focus on… Kk or K-ε Based on the model, different turbulence models were proposed for different airflow organization forms; however, most studies are for small medium and high speed engines, and are four-stroke engines with intake and exhaust valve structures, which are very different from low-speed engines with two-stroke engines and port-valve structures. This leads to significant differences in the movement and organization of airflow in the cylinder, which ultimately directly affects the fuel-air mixing. Summary of the Invention
[0004] This invention provides a method and system for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine. It enables rapid and robust prediction of the vortex level of a two-stroke DC scavenging structure in a marine low-speed engine, provides initial boundary conditions for spray combustion in low-speed engines, and provides a model basis for engine digitization.
[0005] This invention is achieved through the following technical solution: A method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine, the method comprising the following steps: Step 1: Based on the engine model, construct the DC scavenging cylinder vortex velocity field; Step 2: Based on the vortex velocity field inside the DC scavenging cylinder obtained in Step 1, the improved Sigmoid function is used to simulate the velocity field, thereby describing the circumferential velocity change of the vortex inside the cylinder. Step 3: Calculate the theoretical vortex angular momentum based on the circumferential velocity variation of the vortex inside the cylinder as described in Step 2; Step 4: Calculate the eddy angular momentum loss caused by the gas mass loss based on the gas mass loss situation; Step 5: Calculate the eddy angular momentum loss caused by wall friction according to the friction stress formula; Step 6: Calculate the angular momentum loss caused by shearing within the eddy current based on the energy conversion of the eddy current; Step 7: Based on the theoretical vortex angular momentum in Step 3 and the angular momentum loss in Steps 4-6, the prediction of the vortex angular momentum in the cylinder during the low-speed engine scavenging process is realized.
[0006] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 2 specifically involves the following functional formula:
[0007] in It is the circumferential velocity of the vortex inside the cylinder at a certain radius, while This is the maximum circumferential speed, where a and b are calibration parameters. , D Cylinder diameter.
[0008] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 3 specifically involves integrating the vortex angular momentum in space based on a modified Sigmoid velocity field, and deriving the following expression for the vortex angular momentum:
[0009] in, It is the density of the swept-in air. It is the volume occupied by the eddy current.
[0010] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 4 specifically involves determining that the angular momentum loss of the vortex due to mass loss is proportional to the mass of the escaped air. Right now .
[0011] A method for predicting the angular momentum of in-cylinder vortexes during the scavenging process of a marine low-speed engine, wherein step 5 specifically involves using a friction formula for flow on a flat plate to estimate frictional stress, and determining a suitable characteristic length based on a modified Sigmoid velocity field. Dand speed scale The specific formula is as follows:
[0012] in and These are the frictional stresses of the cylinder liner and the piston crown, respectively. and These are the Reynolds numbers applied to the cylinder liner and piston top, respectively. It is the coefficient of friction. It is an empirical constant introduced to account for the difference between the plate and the cylinder wall. It is an empirical constant. This refers to dynamic viscosity.
[0013] A method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine. The friction torque can be obtained from the definition of frictional stress, and the angular momentum loss caused by wall friction during the scavenging process is the integral of the friction torque over time.
[0014]
[0015] in A It is the friction area. r It is the radius. t 0 represents the starting time of the frictional torque. t 1 is the end time of the frictional torque. It is frictional torque. It is the amount of angular momentum loss caused by wall friction.
[0016] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 6 specifically involves the conversion of a portion of the energy of the vortex into turbulent kinetic energy due to internal shearing, wherein the vortex's internal energy loss rate is...
[0017] in It is the density of the swept-in air. It is eddy current mass. It is the circumferential velocity at any radius of the eddy current; The rate at which eddies generate turbulence is,
[0018] Where k swirl It is the turbulent kinetic energy generated by the eddies, G s It is the turbulent kinetic energy generation rate caused by eddies, η s It is the percentage of turbulent kinetic energy generated by the eddy current to its average kinetic energy, u. s It is the maximum circumferential velocity of the eddy, Lj It is the integral length scale of turbulence; Through derivation, we can finally obtain...
[0019] The angular momentum loss caused by shear within the eddy current is,
[0020] in t 0 represents the start time of shearing action within the eddy current. t 1 is the end time of the shearing action within the eddy current.
[0021] A prediction system for the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine includes: The DC scavenging cylinder in-cylinder vortex velocity field module is built according to the engine model. The improved Sigmoid function is used to simulate the velocity field and describe the circumferential velocity change of the vortex in the cylinder. The theoretical vortex angular momentum calculation module calculates the theoretical vortex angular momentum based on the circumferential velocity change of the vortex inside the cylinder. The module for calculating eddy angular momentum loss due to mass loss calculates the resulting eddy angular momentum loss based on the gas mass loss situation. The module for calculating eddy angular momentum loss due to wall friction calculates the eddy angular momentum loss caused by wall friction based on the friction stress formula. The module for calculating angular momentum loss due to shear within eddies calculates the angular momentum loss caused by shear within eddies based on the energy conversion of eddies. The in-cylinder vortex angular momentum prediction module for the low-speed engine scavenging process predicts the in-cylinder vortex angular momentum based on theoretical vortex angular momentum, vortex angular momentum loss due to mass loss, vortex angular momentum loss due to wall friction, and angular momentum loss due to vortex shear.
[0022] An electronic device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to perform the steps of the method described above.
[0023] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the method described above. The beneficial effects of this invention are: Based on the principle of conservation of angular momentum and the ideal in-cylinder vortex velocity distribution, this invention proposes a simple method for predicting vortex angular momentum, which can achieve rapid and accurate prediction of vortex angular momentum for marine low-speed engines.
[0024] This invention proposes an ideal in-cylinder vortex velocity field based on a modified Sigmoid function. By changing the model parameters, it can be adapted to different low-speed engine models, thus achieving the universality of the prediction method of this invention. Attached Figure Description
[0025] Figure 1 This is a flowchart of the method of the present invention.
[0026] Figure 2 This is a schematic diagram of the eddy current velocity field inside the DC sweeping cylinder of the present invention.
[0027] Figure 3 This is the eddy angular momentum result obtained by the prediction method of this invention. Detailed Implementation
[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0029] Example 1 A method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine, the method comprising the following steps: Step 1: Taking a certain marine low-speed engine as the research object, analyze the changes and distribution of the airflow velocity in the cylinder during the scavenging process, and build a DC scavenging cylinder vortex velocity field according to the engine model; Step 2: Based on the vortex velocity field inside the DC scavenging cylinder obtained in Step 1, the improved Sigmoid function is used to simulate the velocity field, thereby describing the circumferential velocity change of the vortex inside the cylinder. Step 3: Calculate the theoretical vortex angular momentum based on the circumferential velocity variation of the vortex inside the cylinder as described in Step 2; Step 4: Calculate the eddy angular momentum loss caused by the gas mass loss based on the gas mass loss situation; Step 5: Calculate the eddy angular momentum loss caused by wall friction according to the friction stress formula; Step 6: Calculate the angular momentum loss caused by shearing within the eddy current based on the energy conversion of the eddy current; Step 7: Based on the theoretical vortex angular momentum in Step 3 and the angular momentum loss in Steps 4-6, the prediction of the vortex angular momentum in the cylinder during the low-speed engine scavenging process is realized.
[0030] A method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine. Step 2 specifically involves analyzing the in-cylinder velocity contour map of the low-speed engine. It can be concluded that the circumferential velocity of the in-cylinder vortex is almost constant in the axial direction, while gradually increasing radially from the cylinder center to the cylinder wall. Near the cylinder wall, due to wall friction, the velocity does not increase further. (See [link to relevant documentation]). Figure 2 As shown, the function formula is as follows:
[0031] in It is the circumferential velocity of the vortex inside the cylinder at a certain radius, while This is the maximum circumferential speed, where a and b are calibration parameters. , D Cylinder diameter.
[0032] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 3 specifically involves integrating the vortex angular momentum in space based on a modified Sigmoid velocity field, and deriving the following expression for the vortex angular momentum:
[0033] in, It is the density of the swept-in air. It is the volume occupied by the eddy current.
[0034] A method for predicting the vortex angular momentum in the cylinder during the scavenging process of a marine low-speed engine, wherein step 4 specifically involves the fact that the scavenging time of the marine low-speed engine is long and the exhaust valve remains open for an extended period, leading to the escape of some air. The greater the amount of air escaped, the greater the loss of vortex angular momentum. The vortex angular momentum loss due to mass loss is directly proportional to the mass of the escaped air. Right now .
[0035] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 5 specifically involves calculating the angular momentum loss caused by wall friction. During its motion, the vortex is constantly in contact with the cylinder wall (including the cylinder bushing and piston top), generating wall friction under frictional stress, which in turn leads to a continuous decay of angular momentum. A suitable method for calculating frictional stress is crucial for solving the angular momentum loss caused by wall friction. Therefore, this invention uses the friction formula for flow on a flat plate to estimate the frictional stress and determines a suitable characteristic length based on a modified Sigmoid velocity field. D and circumferential velocity The specific formula is as follows:
[0036] in and These are the frictional stresses of the cylinder liner and the piston crown, respectively. and These are the Reynolds numbers applied to the cylinder liner and piston top, respectively. It is the coefficient of friction. It is an empirical constant introduced to account for the difference between the plate and the cylinder wall. It is an empirical constant. This refers to dynamic viscosity.
[0037] A method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine is proposed. The friction torque can be obtained from the definition of frictional stress, and the angular momentum loss caused by wall friction during the scavenging process is the integral of the friction torque over time.
[0038]
[0039]
[0040] in A It is the friction area. r It is the radius. t 0 represents the starting time of the frictional torque. t 1 is the end time of the frictional torque, M wall_friction It is the frictional torque, L wall_friction It is the amount of angular momentum loss caused by wall friction.
[0041] A method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, wherein step 6 specifically involves calculating the angular momentum loss caused by shear within the vortex; the generation and development of vortices is a process from instability to stability. Under the influence of a velocity gradient, the shear layer inside the vortex generates turbulence, which directly leads to the loss of vortex angular momentum. It can be said that some of the vortex energy is converted into turbulent kinetic energy, i.e. .
[0042] Due to internal shearing, a portion of the energy in an eddy current is converted into turbulent kinetic energy. The internal energy loss rate of an eddy current is [missing information].
[0043] in It is the density of the swept-in air. It is eddy current mass. It is the circumferential velocity at any radius of the eddy current; The rate at which eddies generate turbulence is,
[0044] Where k swirl It is the turbulent kinetic energy generated by the eddies, G s It is the turbulent kinetic energy generation rate caused by eddies, ηs It is the percentage of turbulent kinetic energy generated by the eddy current to its average kinetic energy, which is calibrated to 0.004, u s It is the maximum circumferential velocity of the eddy, L j It is the turbulence integral length scale, according to the Dulbecco model, we have in These are model calibration parameters V This refers to the cylinder volume.
[0045] By combining the above formulas and deriving the final result, we can obtain:
[0046] The angular momentum loss caused by shear within the eddy current is,
[0047] in t 0 represents the start time of shearing action within the eddy current. t 1 is the end time of the shearing action within the eddy current.
[0048] Example 2 The following experiment demonstrates the effectiveness of the method for predicting the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine, as provided in Embodiment 1 of this application.
[0049] Based on the prediction method for in-cylinder vortex angular momentum during the scavenging process of marine low-speed engines proposed in this application, a comparison was made with existing technologies. Experimental results show that the prediction accuracy of the proposed method is superior to existing methods, while significantly reducing the prediction time. This confirms the effectiveness of the method and provides a model basis for engine digitization. The effect of the above-mentioned prediction method for in-cylinder vortex angular momentum during the scavenging process of marine low-speed engines is illustrated in the figure below. Figure 3 As shown, the solid line represents the vortex angular momentum calculated by the convergege software, while the square, circle, upper triangle, and lower triangle represent the angular momentum values calculated using this prediction method after considering different angular momentum losses. It can be seen that this prediction method can achieve rapid and robust prediction of different angular momentum losses at key nodes in the scavenging process. The prediction method for in-cylinder vortex angular momentum during the scavenging process of marine low-speed engines proposed in this application has universal applicability.
[0050] Example 3 This application provides a prediction system for the angular momentum of in-cylinder vortices during the scavenging process of a marine low-speed engine. The prediction system includes a DC scavenging in-cylinder vortex velocity field module, a theoretical vortex angular momentum calculation module, a vortex angular momentum loss calculation module caused by mass loss, a vortex angular momentum loss calculation module caused by wall friction, a vortex shear loss calculation module caused by angular momentum loss, and a vortex angular momentum prediction module for the scavenging process of a low-speed engine. The DC scavenging cylinder vortex velocity field module, based on the engine model, constructs a DC scavenging cylinder vortex velocity field and uses a modified Sigmoid function to simulate the velocity field, thereby describing the circumferential velocity change of the vortex in the cylinder. The theoretical vortex angular momentum calculation module shown calculates the theoretical vortex angular momentum based on the circumferential velocity change of the vortex inside the cylinder. The eddy angular momentum loss calculation module caused by mass loss calculates the resulting eddy angular momentum loss based on the gas mass loss situation. The eddy current angular momentum loss calculation module caused by wall friction calculates the eddy current angular momentum loss caused by wall friction according to the friction stress formula. The module shown calculates the angular momentum loss caused by shear within the eddy current, based on the energy conversion of the eddy current. The in-cylinder vortex angular momentum prediction module for the low-speed engine scavenging process predicts the in-cylinder vortex angular momentum based on theoretical vortex angular momentum, vortex angular momentum loss due to mass loss, vortex angular momentum loss due to wall friction, and angular momentum loss due to vortex shear.
[0051] As can be seen from the above, the embodiments of this application provide a prediction system for the in-cylinder vortex angular momentum during the scavenging process of marine low-speed engines. It proposes a computationally simple vortex angular momentum prediction module, enabling rapid and accurate prediction of the vortex angular momentum of marine low-speed engines. Furthermore, the ideal in-cylinder vortex velocity field proposed based on the improved Sigmoid function can be adapted to different low-speed engine models by changing the model parameters, achieving the universality of this prediction method. In addition, the prediction accuracy of the in-cylinder vortex angular momentum prediction system for the scavenging process of marine low-speed engines in the embodiments of this application is superior to existing methods, while the prediction time is significantly shortened, realizing the prediction of the in-cylinder vortex angular momentum during the scavenging process of low-speed engines.
[0052] Example 4 This application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor. The memory stores software programs and modules, and the processor executes various functional applications and data processing by running the software programs and modules stored in the memory. The memory and processor are connected via a bus. Specifically, the processor implements any of the steps in Embodiment 1 by running the computer program stored in the memory.
[0053] It should be understood that, in the embodiments of this application, the processor may be a Central Processing Unit (CPU), but it may also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.
[0054] Memory may include read-only memory, flash memory, and random access memory, and provides instructions and data to the processor. Some or all of the memory may also include non-volatile random access memory.
[0055] As can be seen from the above, the electronic device provided in this application embodiment can realize the prediction method of the angular momentum of the vortex in the cylinder during the scavenging process of a marine low-speed engine as described in Embodiment 1 by constructing a DC scavenging cylinder vortex velocity field, thus obtaining a result different from... Kk or K-ε The model describes the circumferential velocity variation of the vortex within the cylinder during low-speed engine spray combustion. By calculating the vortex angular momentum prediction using a simplified method and proposing an ideal in-cylinder vortex velocity field based on a modified Sigmoid function, the model parameters can be changed to adapt to different low-speed engine models. This not only achieves rapid and accurate prediction of the vortex angular momentum for marine low-speed engines but also demonstrates the universality of the prediction method of this invention.
[0056] It should be understood that if the integrated modules / units described above are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable storage medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction.
[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use 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 disclosed herein.
[0058] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the above device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.
[0059] It should be noted that the methods and detailed examples provided in the above embodiments can be incorporated into the apparatus and devices provided in the embodiments, and can be referred to each other, without further elaboration.
[0060] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.
[0061] In the embodiments provided in this application, it should be understood that the disclosed apparatus / terminal devices and methods can be implemented in other ways. For example, the apparatus / device embodiments described above are merely illustrative. For instance, the division of the modules or units described above is merely a logical functional division, and in actual implementation, it can be divided in other ways. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed.
[0062] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.
Claims
1. A method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine, characterized in that, The prediction method includes the following steps: Step 1: Based on the engine model, construct the DC scavenging cylinder vortex velocity field; Step 2: Based on the vortex velocity field inside the DC scavenging cylinder obtained in Step 1, the improved Sigmoid function is used to simulate the velocity field, thereby describing the circumferential velocity change of the vortex inside the cylinder. Step 3: Calculate the theoretical vortex angular momentum based on the circumferential velocity variation of the vortex inside the cylinder as described in Step 2; Step 4: Calculate the eddy angular momentum loss caused by the gas mass loss based on the gas mass loss situation; Step 5: Calculate the eddy angular momentum loss caused by wall friction according to the friction stress formula; Step 6: Calculate the angular momentum loss caused by shearing within the eddy current based on the energy conversion of the eddy current; Step 7: Based on the theoretical vortex angular momentum in Step 3 and the angular momentum loss in Steps 4-6, the prediction of the vortex angular momentum in the cylinder during the low-speed engine scavenging process is realized. Step 2 specifically involves the following function formula: in It is the circumferential velocity of the vortex inside the cylinder at a certain radius, while This is the maximum circumferential speed, where a and b are calibration parameters. , D Cylinder diameter, r It is the radius; Step 3 specifically involves integrating the vortex angular momentum in space based on the improved Sigmoid velocity field, and deriving the final expression for the vortex angular momentum as follows: in, It is the density of the swept-in air. It is the volume occupied by the eddy current. It is the circumferential velocity at any radius of the eddy.
2. The method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine according to claim 1, characterized in that, Specifically, step 4 involves the eddy angular momentum loss caused by mass loss being proportional to the mass of the escaping air. Right now .
3. The method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine according to claim 1, characterized in that, Step 5 specifically involves using the friction formula for flow on a flat plate to estimate the frictional stress, and determining the cylinder diameter based on the modified Sigmoid velocity field. D and the circumferential velocity of the vortex inside the cylinder at a certain radius or maximum circumferential velocity The specific formula is as follows: in and These are the frictional stresses of the cylinder liner and the piston crown, respectively. and These are the Reynolds numbers applied to the cylinder liner and piston top, respectively. It is the coefficient of friction. It is an empirical constant introduced to account for the difference between the plate and the cylinder wall. It is an empirical constant. This refers to dynamic viscosity.
4. The method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine according to claim 3, characterized in that, Frictional torque can be obtained from the definition of frictional stress, and the angular momentum loss caused by wall friction during the scavenging process is the integral of frictional torque over time. in A It is the friction area. r It is the radius. t 0 represents the starting time of the frictional torque. t 1 is the end time of the frictional torque, M wall_friction It is the frictional torque, L wall_friction It is the amount of angular momentum loss caused by wall friction.
5. The method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine according to claim 1, characterized in that, Specifically, step 6 involves the eddy current converting a portion of its energy into turbulent kinetic energy due to internal shearing, wherein the eddy current loses more internal energy than the turbulent energy. for, in It is the density of the swept-in air. It is eddy current mass. It is the circumferential velocity at any radius of the eddy current; The rate at which eddies generate turbulence is, in It is the turbulent kinetic energy generated by eddies. It is the turbulent kinetic energy generation rate caused by eddies. It is the percentage of turbulent kinetic energy generated by eddies to their average kinetic energy. It is the maximum circumferential velocity of the eddy. It is the integral length scale of turbulence; Through derivation, we can finally obtain... The angular momentum loss caused by shear within the eddy current is, in t 0 represents the start time of shearing action within the eddy current. t 1 is the end time of the shearing action within the eddy current.
6. A prediction system for the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine, characterized in that, The prediction system uses a method for predicting the angular momentum of in-cylinder vortex during the scavenging process of a marine low-speed engine as described in any one of claims 1-5. The prediction system includes: The DC scavenging cylinder in-cylinder vortex velocity field module is built according to the engine model. The improved Sigmoid function is used to simulate the velocity field and describe the circumferential velocity change of the vortex in the cylinder. The theoretical vortex angular momentum calculation module calculates the theoretical vortex angular momentum based on the circumferential velocity change of the vortex inside the cylinder. The module for calculating eddy angular momentum loss due to mass loss calculates the resulting eddy angular momentum loss based on the gas mass loss situation. The module for calculating eddy angular momentum loss due to wall friction calculates the eddy angular momentum loss caused by wall friction based on the friction stress formula. The module for calculating angular momentum loss due to shear within eddies calculates the angular momentum loss caused by shear within eddies based on the energy conversion of eddies. The in-cylinder vortex angular momentum prediction module for the low-speed engine scavenging process predicts the in-cylinder vortex angular momentum based on theoretical vortex angular momentum, vortex angular momentum loss due to mass loss, vortex angular momentum loss due to wall friction, and angular momentum loss due to vortex shear.
7. An electronic device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor, when executing the computer program, implements the steps of the method as claimed in any one of claims 1 to 5.
8. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 5.