Method for establishing the theoretical model of ventilation for overhead valve two-stroke aviation heavy fuel oil engine

Abstract

The present invention discloses a method for establishing a theoretical ventilation model for an overhead valve two-stroke aviation heavy fuel oil engine, comprising the following steps: establishing a NewBenson correction model; determining a mathematical model describing a scavenging phase based on the NewBenson correction model; determining a simulated change process of each stage and each zone of the simulated scavenging phase using calculation results of a three-dimensional simulation model; combining the mathematical model with a regression fitting method to obtain mathematical expressions for the model characteristic coefficients of the instantaneous air mixing ratio, the instantaneous exhaust gas mixing ratio, and the mixed gas exhaust rate; and combining the mathematical expressions for the model characteristic coefficients of the instantaneous air mixing ratio, the instantaneous exhaust gas mixing ratio, and the mixed gas exhaust rate into the mathematical model describing the scavenging phase to establish a theoretical ventilation model. The theoretical model obtained by the present invention has high prediction accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of overhead valve two-stroke aviation heavy oil engines, in particular to a method for establishing a ventilation theoretical model of an overhead valve two-stroke aviation heavy oil engine. Background Art

[0002] Aviation heavy fuel oil engines specifically refer to aviation piston engines that use diesel or kerosene as fuel. Overhead valve two-stroke aviation heavy fuel oil engines no longer have an air port structure. Their intake and exhaust valves are arranged on the cylinder head. They have traditional advantages such as high specific power and good torque uniformity. In addition, they have the advantages of low lubricating oil consumption and flexible and controllable valve timing, and have broad application prospects. Figure 11 It shows the overhead valve two-stroke ventilation form.

[0003] The ventilation process of a two-stroke aviation heavy fuel oil engine refers to the entire process of replacing the exhaust gas in the cylinder with fresh charge (air). It begins when the exhaust valve opens (for exhaust valve type) or the exhaust port opens (for piston-controlled port type) and ends when both the intake and exhaust ports (doors) close. The ventilation process can be divided into three stages: from the opening of the exhaust port (door) to the opening of the intake port (door) is called the "free exhaust phase"; from the opening of the intake port (door) to the closing of either the intake or exhaust port (door) is called the "scavenging phase"; and the remaining stage is called the "post-charge phase" or "post-exhaust phase" until all intake and exhaust ports (doors) are closed. The ventilation process is one of the key links affecting the performance of two-stroke aviation heavy fuel oil engines.

[0004] A theoretical ventilation model is a one-dimensional model that describes the evolution of parameters such as charging efficiency, air supply ratio, and exhaust gas purity during the ventilation process, or the relationships between them. It can quickly predict the overall characteristics of the ventilation process under different parameters and operating conditions, and can replace three-dimensional simulation models to quickly analyze in-cylinder gas evolution. Establishing a reliable theoretical ventilation model is crucial for analyzing and optimizing the factors affecting the ventilation process.

[0005] Existing theoretical models for predicting the overall characteristics of the ventilation process include the New Benson model, the Benson / Bradham model, the Crest model, the Kyrtatos / Koumbarelis model, and the New Kyrtatos / Koumbarelis model. The prediction results of the New Benson model, the Benson / Bradham model, the Crest model, the Kyrtatos / Koumbarelis model, and the New Kyrtatos / Koumbarelis model are compared with the calculation results of the three-dimensional simulation model of the ventilation process of the overhead valve two-stroke aviation heavy fuel oil engine, and the following are obtained: Figures 12 to 19 The results shown. Figures 12 to 19It can be seen that the existing theoretical models are unable to accurately predict the changes in charging efficiency, exhaust purity, gas quality, etc. during the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine.

[0006] Among them, the New Benson model divides the scavenging process into three stages and three partitions, such as Figure 20 The main reasons for the deviation of the NewBenson model in predicting the ventilation process of overhead valve two-stroke aviation heavy fuel oil engines are as follows. First, the New Benson model's first phase is too long. In overhead-valve, two-stroke aviation heavy fuel oil (HFO) engines, fresh charge begins to overflow from the exhaust port at a normalized time of 0.2. Second, the New Benson model simply considers the exhaust in the second phase to be pure air and the exhaust in the third phase to be a mixture. These assumptions are inaccurate. Since the composition of the gas passing through the exhaust valve should not change suddenly, the exhaust gas in the second phase should contain exhaust gas components and the exhaust gas in the third phase should also contain pure air components. In overhead-valve, two-stroke aviation heavy fuel oil engines, the short-circuiting of the fresh charge (air) occurs early and persists for a long time, resulting in exhaust as a mixture in the second phase and pure air in the third phase. Therefore, the New Benson model's assumptions about the exhaust gas composition in the second and third phases contribute to the prediction error. Third, the New Benson model considers the model characteristic coefficients describing the rate at which gases from the air and exhaust zones enter the mixing zone in the three phases as fixed constants or simply linearly varying with the zone volume. This is also inaccurate and contributes to the prediction error. The method for establishing a theoretical model of the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine proposed in the present invention is based on a correction of the New Benson model. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one object of the present invention is to provide a method for establishing a theoretical model for the ventilation of an overhead valve two-stroke aviation heavy fuel oil engine. This method can produce a theoretical model for predicting the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine. The resulting theoretical model has high prediction accuracy and can effectively capture the characteristics of the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine.

[0008] The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to an embodiment of the present invention comprises the following steps:

[0009] S1: Establishing a New Benson correction model: Dividing the cylinder volume in the scavenging phase into an air zone, a mixing zone, and an exhaust zone, and dividing the scavenging phase into a first stage, a second stage, and a third stage, wherein the exhaust in the first stage is the exhaust gas in the exhaust zone; the exhaust in the second stage is the mixed gas in the mixing zone and the exhaust gas in the exhaust zone, and the proportion of the mixed gas in the exhaust in the second stage gradually increases, while the proportion of the exhaust gas gradually decreases; the exhaust in the third stage is the air in the air zone and the mixed gas in the mixing zone, and the proportion of the air in the exhaust in the third stage first increases and then decreases, while the proportion of the mixed gas first decreases and then increases;

[0010] S2: determining a mathematical model describing the scavenging phase based on the New Benson correction model, wherein the mathematical model includes a model characteristic coefficient for controlling an instantaneous mixing ratio of air from the air zone entering the mixing zone, a model characteristic coefficient for controlling an instantaneous mixing ratio of exhaust gas from the exhaust zone entering the mixing zone, and a model characteristic coefficient for characterizing a mixed gas exhaust rate at a certain moment;

[0011] S3: Determine the simulation change process of each stage and each zone in the simulated scavenging stage based on the calculation results of the three-dimensional simulation model, and combine the mathematical model to obtain the change relationship of the model characteristic coefficient of the instantaneous air mixing ratio, the change relationship of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio, and the change relationship of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment, and obtain the mathematical expression of the model characteristic coefficient of the instantaneous air mixing ratio, the mathematical expression of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio, and the mathematical expression of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment through regression fitting;

[0012] S4: Combine the mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of the air, the mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of the exhaust gas, and the mathematical expression of the model characteristic coefficient representing the exhaust rate of the mixed gas at a certain moment into the mathematical model describing the scavenging stage to establish a ventilation theory model.

[0013] The method for establishing a theoretical ventilation model for an overhead valve two-stroke aviation heavy fuel oil engine according to an embodiment of the present invention has the following advantages: First, by adjusting the exhaust composition of the second stage of the scavenging phase to a combination of mixed gas and exhaust gas, and the exhaust composition of the third stage to a combination of mixed gas and air, the exhaust composition does not undergo a sudden change, and by introducing a model characteristic coefficient to characterize the proportion of mixed gas in the exhaust at a certain moment, the obtained ventilation theoretical model is more suitable for describing the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine. Second, the simulation change process of each stage and zone of the simulated scavenging phase is determined by the calculation results of the three-dimensional simulation model. In combination with the mathematical model, the model characteristic coefficients of the instantaneous air mixing ratio, the model characteristic coefficients of the instantaneous exhaust gas mixing ratio, and the model characteristic coefficients characterizing the mixed gas exhaust ratio at a certain moment are obtained. Finally, the ventilation theoretical model is established. The obtained ventilation theoretical model captures the characteristics of the early onset and long duration of fresh charge loss in the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine. Compared with other ventilation theoretical models, the prediction accuracy of the ventilation change process of an overhead valve two-stroke aviation heavy fuel oil engine is significantly improved. Third, the theoretical ventilation model obtained can quickly predict the overall characteristics of the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine, and can replace the three-dimensional simulation model to quickly and accurately analyze the changes in the gas in the cylinder during the ventilation process.

[0014] According to some embodiments of the present invention, in step S2, the mathematical model includes a mathematical expression of a gas mass change relationship, a mathematical expression of a cylinder pressure change relationship, a mathematical expression of a gas temperature change relationship, a mathematical expression of a gas volume change relationship, and a mathematical expression of a gas exchange process parameter;

[0015] In step S4, the ventilation theoretical model includes one or more of a gas mass change theoretical model, a cylinder pressure change theoretical model, a gas temperature change theoretical model, a gas volume change theoretical model, and a ventilation process parameter theoretical model.

[0016] According to some embodiments of the present invention, the mathematical expression of the gas mass change relationship includes a mathematical expression of the total gas mass of the mixing zone in the first stage, the second stage, and the third stage, a mathematical expression of the air mass of the mixing zone, a mathematical expression of the exhaust gas mass of the mixing zone, a mathematical expression of the air mass of the air zone, and a mathematical expression of the exhaust gas mass of the exhaust zone; the mathematical expression of the ventilation process parameter includes a mathematical expression of the exhaust gas purity;

[0017] The variation relationship of the model characteristic coefficient of the instantaneous air mixing ratio and the variation relationship of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio are specifically obtained by combining the simulation variation process of each zone in each stage of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model with the mathematical expression of the total gas mass of the mixing zone in the first stage, the second stage, and the third stage, the mathematical expression of the air mass in the mixing zone, the mathematical expression of the exhaust gas mass in the mixing zone, the mathematical expression of the air mass in the air zone, and the mathematical expression of the exhaust gas mass in the exhaust zone;

[0018] The change relationship of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment is obtained by combining the simulation change process of each stage and each zone of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model with the cylinder instantaneous intake flow, the cylinder instantaneous exhaust flow and the mathematical expression of the exhaust purity.

[0019] According to some embodiments of the present invention, the mathematical expression of the gas temperature change relationship includes the mathematical expression of the gas temperature of the mixing zone in the first stage, the second stage and the third stage, the mathematical expression of the air temperature of the air zone and the mathematical expression of the exhaust gas temperature of the exhaust gas zone; the mathematical expression of the gas volume change relationship includes the mathematical expression of the gas volume of the mixing zone in the first stage, the second stage and the third stage, the mathematical expression of the air volume of the air zone and the mathematical expression of the exhaust gas volume of the exhaust gas zone.

[0020] According to some embodiments of the present invention, the mathematical expression of the ventilation process parameter further includes a mathematical expression of the air supply ratio, a mathematical expression of the charging efficiency, and a mathematical expression of the capture rate.

[0021] According to some embodiments of the present invention, the mathematical expression of the air supply ratio is:

[0022]

[0023] In formula (1), l0 is the real-time air supply ratio, is the real-time total mass of air entering the cylinder per cycle, p a is the intake pressure, V c is the maximum volume in the cylinder, R is the ratio of the molar gas constant to the molecular weight of air, T a is the intake air temperature;

[0024] The mathematical expression of the charging efficiency is:

[0025]

[0026] In formula (2), η cis the real-time inflation efficiency, T a is the intake air temperature, m 2n is the gas mass in the air zone at the current step length, m 1an is the mass of air in the mixing zone at the current step length, R is the ratio of the molar gas constant to the molecular weight of air, and p a is the intake pressure, V c is the maximum volume in the cylinder;

[0027] The mathematical expression of the exhaust gas purity in the first stage is:

[0028] β n =0(3.1);

[0029] The mathematical expression of the exhaust gas purity in the second stage is:

[0030]

[0031] The mathematical expression of the exhaust gas purity in the third stage is:

[0032]

[0033] In formula (3.1), formula (3.2) and formula (3.3), β n is the exhaust purity of the current step, b3 is the model characteristic coefficient that characterizes the exhaust rate of the mixed gas at a certain moment, is the instantaneous exhaust volume, m 1an is the mass of air in the mixing zone at the current step length, m 1bn is the mass of exhaust gas in the mixing zone at the current step length.

[0034] According to some embodiments of the present invention, in step S3, determining the simulation change process of each stage and each zone of the simulated scavenging stage through the calculation results of the three-dimensional simulation model includes using a component transport model in the ventilation flow simulation model to perform a simulation calculation process.

[0035] According to some embodiments of the present invention, the simulation calculation process using the component transport model in the ventilation flow simulation model specifically includes the following sub-steps:

[0036] S301: setting the average mass fraction of carbon dioxide in the simulated cylinder space at the start of the simulated scavenging phase as the initial mass fraction, defining a region in the simulated cylinder space where the carbon dioxide mass fraction is greater than 95%-100% of the initial mass fraction as a simulated exhaust gas region, and defining a region in the simulated cylinder space where the carbon dioxide mass fraction is lower than 100%-105% of the average mass fraction of carbon dioxide in the air charged into the simulated cylinder space as a simulated air region, so as to calculate the volumes of the simulated air region and the simulated exhaust gas region at any moment, and defining the region of the simulated cylinder space excluding the simulated exhaust gas region and the simulated air region as a simulated mixing region;

[0037] S302: Calculating the gas masses of the simulated air zone and the simulated exhaust zone based on the volumes of the simulated air zone and the simulated exhaust zone at any moment, wherein the volume of the simulated mixing zone is the total volume of the space in the simulated cylinder minus the volumes of the simulated air zone and the simulated exhaust zone, and the mass of the simulated mixing zone is the total mass of the gas in the space in the simulated cylinder minus the gas masses of the simulated air zone and the gas masses of the simulated exhaust zone;

[0038] S303: Starting from the simulated scavenging phase, with a certain crankshaft angle as a calculation step, the simulated change process is calculated.

[0039] According to some embodiments of the present invention, in step S3, the mathematical expression of the model characteristic coefficient of the instantaneous air mixing ratio obtained by regression fitting is:

[0040]

[0041] In formula (4), b1 is the model characteristic coefficient of the instantaneous air mixing rate, τ is the normalized time of the scavenging stage, ξ1 and k1 are constants;

[0042] The mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of the exhaust gas obtained by regression fitting includes the following steps: dividing the exhaust gas from the exhaust zone entering the mixing zone into a first sub-process and a second sub-process, considering that in the first sub-process, the exhaust gas from the exhaust zone is entrained and infiltrated by the air jet charged into the cylinder, and in the second sub-process, the exhaust gas from the exhaust zone is normally mixed into the mixing zone, and the following is obtained by analysis and fitting:

[0043]

[0044] In formula (5), b2 is the model characteristic coefficient of the instantaneous mixing rate of the exhaust gas, τ g is the end time of the first sub-process, τ1 is the normalized time of the second sub-process, ξ2 and k2 are constants;

[0045] The mathematical expression of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment obtained by regression fitting includes the following steps:

[0046] Considering that the change of exhaust gas components is continuous, the exhaust gas in the first stage of the scavenging stage is all waste gas. In the second stage, the proportion of the mixed gas in the exhaust gas gradually increases. In the early stage of the third stage, the short circuit of air increases rapidly, and the proportion of the mixed gas in the exhaust gas decreases. In the late stage of the third stage, the exhaust gas purity slowly decreases in a linear relationship. The analysis and fitting results are:

[0047]

[0048] In formula (6), b3 is the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment, τ2 represents the normalized time of the second stage and the third stage, τ3 represents the normalized time of the third stage, τ4 is the normalized time of the late third stage, τ β1 is the end time of the second stage, τ β2 is the end time of the early stage of the third stage; ξ3 and ξ4 are constants, and k3, k4 and k5 are constants.

[0049] According to some embodiments of the present invention, the values ​​of ξ1, ξ2, ξ3 and ξ4 and the values ​​of k1 and k2 vary with the operating conditions of the overhead valve two-stroke aviation heavy fuel oil engine, and the values ​​of ξ1, ξ2, ξ3 and ξ4 and the values ​​of k1 and k2 are determined based on the Gauss-Newton iteration method according to the simulation calculation results of the three-dimensional simulation model.

[0050] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0052] Figure 1 Schematic diagram of the New Benson correction model established by the method for establishing the theoretical model of ventilation of an overhead valve two-stroke aviation heavy fuel oil engine according to an embodiment of the present invention.

[0053] Figure 2 This is a schematic diagram of the change in cylinder gas mass during the ventilation process in the method for establishing a ventilation theoretical model of an overhead valve two-stroke aviation heavy fuel oil engine according to an embodiment of the present invention.

[0054] Figure 3A comparison chart of the predicted results of the New Benson modified theoretical model established in the present invention for the mass changes in the mixing zone, air zone and exhaust gas zone in the scavenging stage and the results obtained by the three-dimensional simulation model.

[0055] Figure 4 The absolute deviation between the mass changes in the mixing zone, air zone and exhaust zone predicted by the New Benson modified theoretical model established by the present invention and the results obtained by the three-dimensional simulation model.

[0056] Figure 5 A comparison chart of the prediction results of the ventilation performance parameters in the scavenging phase by the New Benson modified theoretical model established in the present invention, the results obtained by the three-dimensional simulation model, and the results obtained by the New Benson model.

[0057] Figure 6 The absolute deviation between the filling efficiency and capture rate predicted by the New Benson modified theoretical model established for the present invention and the results obtained by the three-dimensional simulation model.

[0058] Figure 7 A comparison chart of the prediction results of the New Benson modified theoretical model for the exhaust purity in the scavenging stage established in the present invention, the results obtained by the three-dimensional simulation model, and the results obtained by the New Benson model.

[0059] Figure 8 This is a comparison diagram of the cylinder pressure change curve predicted by the New Benson modified theoretical model established by the present invention and the result obtained by the three-dimensional simulation model.

[0060] Figure 9 This is a comparison diagram of the temperature change curves of the mixing zone, air zone and exhaust gas zone in the cylinder predicted by the New Benson modified theoretical model established by the present invention, as well as the average temperature change curve in the cylinder predicted by the New Benson modified theoretical model and the results obtained by the three-dimensional simulation model.

[0061] Figure 10 This is a comparison diagram between the curve drawn according to the mathematical expressions of b1, b2 and b3 in the embodiment of the present invention and the change curves of b1, b2 and b3 obtained by the calculation results of the three-dimensional simulation model.

[0062] Figure 11 It is an overhead valve two-stroke ventilation form.

[0063] Figure 12 This is a comparison chart of the prediction results of the New Benson model, Benson / Bradham model, and Crest model in the existing technology on the change of the charging efficiency in the scavenging stage and the results obtained by the three-dimensional simulation model.

[0064] Figure 13 It is the absolute deviation between the prediction results of the New Benson model, Benson / Bradham model and Crest model for the change of charging efficiency in the scavenging phase in the existing technology and the results obtained by the three-dimensional simulation model.

[0065] Figure 14 This is a comparison chart of the prediction results of the New Benson model, Benson / Bradham model, and Crest model in the existing technology on the change of exhaust purity in the scavenging stage and the results obtained by the three-dimensional simulation model.

[0066] Figure 15 It is the absolute deviation between the prediction results of the New Benson model, Benson / Bradham model and Crest model for the exhaust purity change in the scavenging stage in the prior art and the results obtained by the three-dimensional simulation model.

[0067] Figure 16 This is a comparison chart of the prediction results of the Kyrtatos / Koumbarelis model in the prior art for the mass changes in the mixing zone, air zone and exhaust gas zone during the scavenging phase and the results obtained by the three-dimensional simulation model.

[0068] Figure 17 It is the absolute deviation between the prediction results of the Kyrtatos / Koumbarelis model in the prior art for the mass changes in the mixing zone, air zone and exhaust gas zone in the scavenging phase and the results obtained by the three-dimensional simulation model.

[0069] Figure 18 This is a comparison chart of the prediction results of the Kyrtatos / Koumbarelis model and the New Kyrtatos / Koumbarelis model in the prior art for the change in exhaust purity during the scavenging phase and the results obtained by the three-dimensional simulation model.

[0070] Figure 19 It is the absolute deviation between the prediction results of the Kyrtatos / Koumbarelis model and the New Kyrtatos / Koumbarelis model for the exhaust purity change in the scavenging phase in the prior art and the results obtained by the three-dimensional simulation model.

[0071] Figure 20 This is a schematic diagram showing the New Benson model in the prior art dividing the scavenging process into three stages and three partitions. DETAILED DESCRIPTION

[0072] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0073] The following combination Figures 1 to 10 The method for establishing the ventilation theory model of the overhead valve two-stroke aviation heavy fuel oil engine of the present invention is described.

[0074] like Figures 1 to 10 As shown, the method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to an embodiment of the present invention includes the following steps:

[0075] S1: Establish New Benson modified model: Figure 1 As shown, the cylinder volume in the scavenging stage is divided into an air zone, a mixing zone, and an exhaust zone, and the scavenging stage is divided into a first stage, a second stage, and a third stage. The exhaust in the first stage is the exhaust gas in the exhaust zone; the exhaust in the second stage is the mixed gas in the mixing zone and the exhaust gas in the exhaust zone. The proportion of the mixed gas in the exhaust in the second stage gradually increases, while the proportion of the exhaust gas gradually decreases. The exhaust in the third stage is the air in the air zone and the mixed gas in the mixing zone. The proportion of air in the exhaust in the third stage first increases and then decreases, while the proportion of the mixed gas first decreases and then increases.

[0076] S2: Based on the New Benson modified model, a mathematical model describing the scavenging phase is determined, wherein the mathematical model includes a model characteristic coefficient for controlling the instantaneous mixing ratio of air from the air zone entering the mixing zone, a model characteristic coefficient for controlling the instantaneous mixing ratio of exhaust gas from the exhaust zone entering the mixing zone, and a model characteristic coefficient for characterizing the exhaust rate of the mixed gas at a certain moment;

[0077] S3: Determine the simulation change process of each stage and each zone in the simulated scavenging stage through the calculation results of the three-dimensional simulation model, and combine with the mathematical model to obtain the change relationship of the model characteristic coefficient of the instantaneous air mixing ratio, the change relationship of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio, and the change relationship of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment, and obtain the mathematical expression of the model characteristic coefficient of the instantaneous air mixing ratio, the mathematical expression of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio, and the mathematical expression of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment through regression fitting;

[0078] S4: Combine the mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of air, the mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of exhaust gas, and the mathematical expression of the model characteristic coefficient representing the exhaust rate of the mixed gas at a certain moment into the mathematical model describing the scavenging stage to establish a ventilation theory model.

[0079] It should be noted that the ventilation process can be divided into three stages: the period from the opening of the exhaust port (door) to the opening of the intake port (door) is called the "free exhaust stage"; the period from the opening of the intake port (door) to the closing of either the intake or exhaust port (door) is called the "scavenging stage"; the remaining stage is called the "post-charge stage" or the "post-exhaust stage" until all intake and exhaust ports (doors) are closed. During the ventilation process, the gas composition in the cylinder of the overhead valve two-stroke aviation heavy fuel oil engine changes continuously with the crankshaft angle. In the free exhaust process, there is only exhaust but no intake, and the discharged gas is pure exhaust gas; in the remaining stage, there is only intake but no exhaust, and the incoming gas is fresh charge; therefore, these two processes are relatively simple compared to the scavenging process. The ventilation theoretical model established in the present invention predicts the ventilation performance parameters and gas changes in the scavenging stage of the ventilation process.

[0080] Specifically, the New Benson modified model is established: Figure 1 As shown, the cylinder volume in the scavenging stage is divided into the air zone, the mixing zone and the exhaust zone. It can be understood that here the space in the cylinder of the overhead valve two-stroke aviation heavy fuel oil engine in the scavenging stage is divided into the air zone, the mixing zone and the exhaust zone, wherein the mixing zone refers to the area formed by the edge of the air zone and the exhaust gas in the exhaust zone. The scavenging stage is divided into the first stage, the second stage and the third stage, wherein, as Figure 1 As shown, the exhaust from the first stage is the exhaust gas from the exhaust zone; the exhaust from the second stage is the mixed gas from the mixing zone and the exhaust gas from the exhaust zone. The proportion of the mixed gas in the exhaust from the second stage gradually increases, while the proportion of the exhaust gas gradually decreases. The exhaust from the third stage is the air from the air zone and the mixed gas from the mixing zone. The proportion of air in the exhaust from the third stage first increases and then decreases, while the proportion of the mixed gas first decreases and then increases. It can be understood that by adjusting the exhaust composition of the second stage of the scavenging phase to a combination of mixed gas and exhaust gas, and adjusting the exhaust composition of the third stage to a combination of mixed gas and air, the exhaust composition does not change suddenly, making the established New Benson modified model more suitable for describing the changes in the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine.

[0081] Based on the New Benson modified model, a mathematical model describing the scavenging phase is determined. The mathematical model includes a model characteristic coefficient for controlling the instantaneous mixing rate of air from the air zone entering the mixing zone, a model characteristic coefficient for controlling the instantaneous mixing rate of exhaust gas from the exhaust zone entering the mixing zone, and a model characteristic coefficient for characterizing the mixed gas exhaust rate at a certain moment. Specifically, the model characteristic coefficient for controlling the instantaneous mixing rate of air from the air zone entering the mixing zone is b1, the model characteristic coefficient for controlling the instantaneous mixing rate of exhaust gas from the exhaust zone entering the mixing zone is b2, the model characteristic coefficient for characterizing the mixed gas exhaust rate at a certain moment is b3, and the instantaneous intake rate of the scavenging phase is dm a / dφ, assuming the instantaneous exhaust rate during the scavenging phase is dm e / dφ, then the instantaneous mixing rate of the air in the air zone entering the mixing zone is The instantaneous mixing rate of the exhaust gas from the exhaust zone into the mixing zone is The exhaust rate of the mixed gas in the second and third stages is It should be noted that the above refers to the mass change rate of the gas, so we can get the following: Figure 2 The mass change relationship between each zone at each stage of the ventilation process is shown. Therefore, by introducing the model characteristic coefficient b1 for controlling the instantaneous mixing ratio of air entering the air zone into the mixing zone, the model characteristic coefficient b2 for controlling the instantaneous mixing ratio of exhaust gas entering the exhaust zone, and the model characteristic coefficient b3 for characterizing the mixed gas exhaust rate at a certain moment, the mathematical model describing the scavenging stage can be determined through calculation and deduction.

[0082] The simulation change process of each stage and each zone in the simulated scavenging stage is determined by the calculation results of the three-dimensional simulation model. Combined with the mathematical model, the change relationship of the model characteristic coefficient b1 of the instantaneous mixing rate of air, the change relationship of the model characteristic coefficient b2 of the instantaneous mixing rate of exhaust gas, and the change relationship of the model characteristic coefficient b3 representing the mixed gas exhaust rate at a certain moment are obtained. Through regression fitting, the mathematical expression of the model characteristic coefficient b1 of the instantaneous mixing rate of air, the mathematical expression of the model characteristic coefficient b2 of the instantaneous mixing rate of exhaust gas, and the mathematical expression of the model characteristic coefficient b3 representing the mixed gas exhaust rate at a certain moment are obtained. The simulation change process of each stage and each zone of the simulated scavenging stage is determined by the calculation results of the three-dimensional simulation model. For example, the calculation process of the three-dimensional simulation model can be implemented using existing CFD commercial software and conventional methods. The simulated scavenging stage is obtained by simulating the actual scavenging process of the overhead valve two-stroke aviation heavy fuel oil engine. Therefore, the simulated scavenging stage can also be divided into the first stage, the second stage and the third stage. The cylinder space of the simulated overhead valve two-stroke aviation heavy fuel oil engine in the three-dimensional simulation model when it is in the simulated scavenging stage can also be divided into the simulated air zone, the simulated mixing zone and the simulated exhaust gas zone. Therefore, each stage and each zone refers to the first stage, the second stage and the third stage as well as the simulated air zone, the simulated mixing zone and the simulated exhaust gas zone. From the above, the simulation change process of each stage and each zone of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model can be equivalent to the change process of the scavenging stage of the actual overhead valve two-stroke aviation heavy fuel oil engine, thereby making the change process of the scavenging stage of the actual overhead valve two-stroke aviation heavy fuel oil engine known. By combining the known changing process of the scavenging stage of a two-stroke overhead valve aviation heavy fuel oil engine with the mathematical model used to describe the scavenging stage, we can obtain the changing relationship between the unknown model characteristic coefficient b1 of the instantaneous air mixing ratio, the model characteristic coefficient b2 of the instantaneous exhaust gas mixing ratio, and the model characteristic coefficient b3 representing the mixed gas exhaust rate at a certain moment as the scavenging stage develops and changes. Then, by performing regression fitting on the obtained changing relationship of b1, b2, and b3, we can obtain the mathematical expressions of b1, b2, and b3.

[0083] The mathematical expressions for the model characteristic coefficient b1 of the instantaneous air mixing ratio, the mathematical expression for the model characteristic coefficient b2 of the instantaneous exhaust gas mixing ratio, and the mathematical expression for the model characteristic coefficient b3 representing the mixed gas exhaust rate at a specific moment are combined with the mathematical model describing the scavenging phase to establish a theoretical ventilation model. In other words, by substituting the obtained b1, b2, and b3 into the mathematical model describing the scavenging phase, a theoretical ventilation model can be obtained for calculating the changes in each stage and zone of the scavenging phase in an actual overhead valve two-stroke aviation heavy fuel oil engine. This theoretical ventilation model can also be called the NewBenson modified theoretical model.

[0084] like Figures 3 to 9This is a comparison chart of the prediction results of the New Benson modified theoretical model for the change process of the scavenging stage of the overhead valve two-stroke aviation heavy fuel oil engine and the simulation change process of each stage and zone of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model.

[0085] Figure 3 The figure shows the comparison between the prediction results of the New Benson modified theoretical model on the mass changes in the mixing zone, air zone and exhaust gas zone during the scavenging phase and the results obtained by the three-dimensional simulation model. Figure 4 The absolute deviations between the mass changes in the mixing zone, air zone, and exhaust zone predicted by the New Benson modified theoretical model and the results obtained by the three-dimensional simulation model are as follows. The average absolute deviations of the New Benson modified theoretical model for the mass changes in the mixing zone, air zone, and exhaust zone are 3.5%, 1.9%, and 3.3%, respectively. Figure 3 and Figure 4 It can be seen that the New Benson modified theoretical model obtained by the present invention can accurately predict the mass change process of the mixing zone, air zone and exhaust gas zone in the scavenging stage of the overhead valve two-stroke aviation heavy fuel oil engine.

[0086] Figure 5 This is a comparison chart of the prediction results of the ventilation performance parameters in the scavenging phase by the New Benson modified theoretical model, the results obtained by the three-dimensional simulation model, and the results obtained by the New Benson model, including the charging efficiency curve and the capture rate curve. Figure 6 is the absolute deviation between the aeration efficiency and capture rate predicted by the New Benson modified theoretical model and the results obtained using the 3D simulation model. The New Benson model predicts the capture rate and aeration efficiency curves for an overhead valve two-stroke aviation heavy fuel oil engine with an average absolute deviation of 0.07 and 0.05, respectively. However, the New Benson modified theoretical model predicts capture rate and aeration efficiency curves with an average absolute deviation of only 0.013 and 0.017, respectively, with the maximum deviation not exceeding 0.04. As can be seen from the above, the New Benson modified theoretical model significantly improves the prediction accuracy of the capture rate and aeration efficiency curves for an overhead valve two-stroke aviation heavy fuel oil engine.

[0087] Figure 7The figure is a comparison of the prediction results of the New Benson modified theoretical model for the exhaust purity in the scavenging stage, the results obtained by the three-dimensional simulation model, and the results obtained by the New Benson model. The average absolute deviation of the results of the exhaust purity prediction by the New Benson model and the results obtained by the three-dimensional simulation model is 0.07, while the average absolute deviation of the results of the exhaust purity prediction by the New Benson modified theoretical model in the present invention and the results obtained by the three-dimensional simulation model is 0.02, and the deviation at the maximum deviation does not exceed 0.04. It can be seen from the results that the exhaust purity change process curve predicted by the New Benson modified theoretical model obtained by the present invention is basically consistent with the results obtained by the three-dimensional simulation model, and can express the exhaust purity change law caused by the characteristics of the early occurrence and long duration of the ventilation short circuit of the overhead valve two-stroke aviation heavy oil engine, and also accurately describes the trend and degree of the slight decrease in exhaust purity in the late stage of scavenging.

[0088] Figure 8 This is a comparison chart of the in-cylinder pressure change curve predicted by the New Benson modified theoretical model and the results obtained by the three-dimensional simulation model. Figure 9 The temperature change curves of the mixing zone, air zone and exhaust zone in the cylinder predicted by the New Benson modified theoretical model, as well as the average temperature change curve in the cylinder predicted by the New Benson modified theoretical model, are compared with the results obtained by the three-dimensional simulation model. The 100% normalized cylinder pressure and temperature represent the pressure and temperature at the beginning of the scavenging phase, respectively, and the average cylinder temperature of the three-dimensional simulation model is obtained by mass averaging the temperatures of each zone. The maximum and average absolute deviations of the New Benson modified theoretical model for predicting the cylinder pressure are 8.5% and 3.9% respectively, and the maximum and average absolute deviations of the New Benson modified theoretical model for predicting the cylinder temperature are 8.2% and 4.3% respectively. As can be seen from the above, the New Benson modified theoretical model obtained by the present invention is more accurate in predicting the cylinder pressure and temperature during the ventilation process of the overhead valve two-stroke aviation heavy fuel engine.

[0089] The method for establishing a theoretical ventilation model for an overhead valve two-stroke aviation heavy fuel oil engine according to an embodiment of the present invention has the following advantages: First, by adjusting the exhaust composition of the second stage of the scavenging phase to a combination of mixed gas and exhaust gas, and the exhaust composition of the third stage to a combination of mixed gas and air, the exhaust composition does not undergo a sudden change, and by introducing a model characteristic coefficient b3 to characterize the proportion of mixed gas in the exhaust at a certain moment, the obtained ventilation theoretical model is more suitable for describing the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine. Second, the simulation change process of each stage and zone of the simulated scavenging phase is determined based on the calculation results of the three-dimensional simulation model. Combined with the mathematical model, the model characteristic coefficient b1 of the instantaneous air mixing ratio, the model characteristic coefficient b2 of the instantaneous exhaust gas mixing ratio, and the model characteristic coefficient b3 representing the mixed gas exhaust ratio at a certain moment are obtained. Finally, the ventilation theoretical model is established. The obtained ventilation theoretical model captures the characteristics of the early onset and long duration of fresh charge loss in the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine. Compared with other ventilation theoretical models, the prediction accuracy of the ventilation change process of an overhead valve two-stroke aviation heavy fuel oil engine is significantly improved. Third, the theoretical ventilation model obtained can quickly predict the overall characteristics of the ventilation process of an overhead valve two-stroke aviation heavy fuel oil engine, and can replace the three-dimensional simulation model to quickly and accurately analyze the changes in the gas in the cylinder during the ventilation process.

[0090] According to some embodiments of the present invention, in step S2, the mathematical model includes a mathematical expression of the relationship between gas mass changes, a mathematical expression of the change in cylinder pressure, a mathematical expression of the relationship between gas temperature changes, a mathematical expression of the relationship between gas volume changes, and a mathematical expression of ventilation process parameters.

[0091] Specifically, the mathematical expression of the gas mass change relationship includes the mathematical expression of the total gas mass in the mixing zone in the first stage, the second stage and the third stage, the mathematical expression of the air mass in the mixing zone, the mathematical expression of the exhaust gas mass in the mixing zone, the mathematical expression of the air mass in the air zone and the mathematical expression of the exhaust gas mass in the exhaust zone.

[0092] Mathematical expressions for gas temperature variations include those for the gas temperature in the mixing zone, the air zone, and the exhaust gas temperature in the exhaust zone during the first, second, and third phases. Mathematical expressions for gas volume variations include those for the gas volume in the mixing zone, the air zone, and the exhaust gas volume in the exhaust zone during the first, second, and third phases. Determining these mathematical models allows for the calculation of ventilation process parameters and a comprehensive description of the ventilation process.

[0093] The mathematical expressions of the ventilation process parameters include the mathematical expressions of exhaust purity, air supply ratio, charging efficiency and capture rate, so as to fully describe the ventilation process.

[0094] Specifically, the derivation process of the mathematical model describing the scavenging phase is as follows:

[0095] First, the theoretical model for gas exchange established in this paper uses the following assumptions: 1. The pressure is equal throughout the cylinder, and the ratio of each zone is the ratio of the zone volume to the cylinder volume; 2. The temperature within each zone is uniform, ignoring heat transfer between zones. The specific heat of heat exchange between each zone and the cylinder boundary is constant. The thermal conductivity of the cylinder is determined based on the mass-average temperature of the gas, and the initial temperature of the mixing zone is the cylinder temperature at the start of scavenging; 3. Only a defined mixing mass exchange occurs between zones, and only unidirectional flow is in the indicated direction. 4. The exhaust components are uniformly mixed immediately after passing through the exhaust valve, and the temperature is the mass-average temperature.

[0096] In the mathematical model calculation process, m represents the gas mass. All footnotes are defined as follows: a represents intake (air); c represents cylinder; e represents exhaust; n represents the current step; (n-1) represents the previous step; and the numbers 1-3 represent the mixing zone, air zone, and exhaust zone, respectively.

[0097] The mathematical expression of the gas mass change relationship is as follows:

[0098] Phase 1:

[0099] Total mass of the mixing zone:

[0100]

[0101] The quality of the air in the mixing zone:

[0102]

[0103] Quality of exhaust gas in the mixing zone:

[0104]

[0105] Total mass of air zone:

[0106]

[0107] Total mass of exhaust gas area:

[0108]

[0109] Phase 2:

[0110] Total mass of the mixing zone:

[0111]

[0112] The quality of the air in the mixing zone:

[0113]

[0114] Quality of exhaust gas in the mixing zone:

[0115]

[0116] Total mass of air zone: Total mass of exhaust gas area: Phase 3:

[0117] Total mass of the mixing zone: The mass of air and exhaust gas in the mixing zone m 1an and m 1bn The expression is the same as that of the second stage.

[0118] Total mass of air zone: Total mass of exhaust gas area: The mathematical expression of the cylinder pressure change is derived as follows:

[0119] The total internal energy E in the cylinder is the sum of the internal energy of the air zone, exhaust gas zone and mixing zone:

[0120]

[0121] Among them, T x represents the temperature of the corresponding zone, M is the average molecular weight of the gas in the cylinder, p is the real-time pressure in the cylinder, V x represents the volume of the corresponding area, and R is the ideal gas constant. p 、c v , κ are the specific heat at constant pressure, specific heat at constant volume, and adiabatic coefficient, respectively, and V is the real-time volume in the cylinder. According to the first law of thermodynamics, the energy conservation of the gas in the cylinder satisfies:

[0122]

[0123] Where dQ / dφ is the thermal conductivity of the cylinder; T a and T e are the temperatures of the gases in the cylinder near the intake and exhaust ports, respectively. Then:

[0124]

[0125] exist:

[0126] c p (κ-1) = κR (8.11);

[0127] c p (κ-1)T=κRT=a 2(8.12);

[0128] Finally, the mathematical expression of the pressure change in the cylinder is:

[0129]

[0130] Among them, a a and a e are the local sonic speeds of the gas in the cylinder near the intake and exhaust valves, respectively; p is the real-time pressure in the cylinder; and V is the real-time volume in the cylinder. At any crankshaft angle step, the relationship between the real-time pressure p in the cylinder and the pressure of the previous step can be expressed as:

[0131]

[0132] The derivation process of the mathematical expressions of the gas temperature change relationship and gas volume change relationship in the three stages of the scavenging process is as follows:

[0133] Phase 1:

[0134] The gas in the exhaust zone satisfies the energy conservation law:

[0135]

[0136] The following relationship exists:

[0137]

[0138] Therefore, the energy conservation formula of the gas in the exhaust gas zone is:

[0139]

[0140] Combining the similar terms of dm3 / dφ and dT3 / dφ, we can get

[0141]

[0142] Therefore, the change relationship of the exhaust gas temperature in the exhaust gas area is as follows:

[0143]

[0144] The gas in the air zone satisfies the energy conservation law:

[0145]

[0146] Therefore, the energy conservation equation of the gas in the air zone is:

[0147]

[0148] Conduct DM a Combining the similar terms of / dφ and dT2 / dφ, we can get

[0149] We can get:

[0150]

[0151] Therefore, the relationship between the temperature change in the air zone is as follows:

[0152]

[0153] After obtaining the current step temperature of the air zone and the exhaust zone, the volumes of the two zones can be calculated using the following formula:

[0154]

[0155] Then the volume and temperature of the mixing zone can be obtained:

[0156] V1=V c -(V2+V3)(9.25);

[0157]

[0158] Phase 2:

[0159] The derivation of the temperature relationship in the air zone is the same as that in the first stage, and can be calculated using Equations 9.22 and 9.23.

[0160] The gas in the exhaust zone satisfies the energy conservation law:

[0161]

[0162] Because of the following relationship:

[0163]

[0164] After similar derivation to the first stage, the formulas are combined and rearranged to obtain:

[0165]

[0166]

[0167] It can be seen that this formula is the same as the temperature calculation formula for the exhaust zone in the first stage. Therefore, the volume of the air zone and the exhaust zone, as well as the volume and temperature of the mixing zone are also the same as the calculation method in the first stage.

[0168] Phase 3:

[0169] The gas in the air zone satisfies the energy conservation law:

[0170]

[0171] Because of the following relationship:

[0172]

[0173] Therefore, the energy conservation equation of the gas in the air zone is:

[0174]

[0175] Conduct DM a / dφ、dm e Combining the similar terms of / dφ and dT2 / dφ, we can get:

[0176]

[0177]

[0178] After similar derivation to the first stage, the formulas are combined and rearranged to obtain:

[0179]

[0180] It can be seen that this formula is the same as the air zone in the first and second stages.

[0181] The gas in the exhaust zone satisfies the energy conservation law:

[0182]

[0183] in

[0184]

[0185] After similar derivation to the first stage, the formulas are combined and rearranged to obtain:

[0186]

[0187] This formula is identical to the one used to calculate the exhaust zone temperature in stages 1 and 2. Therefore, the volumes of the air and exhaust zones, as well as the volume and temperature of the mixing zone, are calculated using the same methods as in stages 1 and 2. Derivation shows that the temperature variations in the three zones at each stage are identical.

[0188] The air supply ratio refers to the ratio between the total mass of the fresh charge (air) flowing through the intake valve per cycle and the mass of the fresh charge (air) in the cylinder when the cylinder is completely filled with fresh charge (air) in the intake state. Based on the definition of the air supply ratio, the mathematical expression of the real-time air supply ratio can be obtained as:

[0189]

[0190] In formula (1), l0 is the real-time air supply ratio, is the real-time total mass of air entering the cylinder per cycle, pa is the intake pressure, V c is the maximum volume in the cylinder, R is the ratio of the molar gas constant to the molecular weight of air, T a is the intake air temperature.

[0191] The charging efficiency is the ratio of the total mass of air remaining in the cylinder to the mass of air when the cylinder is completely filled with air under the intake state. Therefore, the mathematical expression of the charging efficiency is:

[0192]

[0193] In formula (2), η c is the real-time inflation efficiency, T a is the intake air temperature, m 2n is the gas mass in the air zone at the current step length, m 1an is the mass of air in the mixing zone at the current step length, R is the ratio of the molar gas constant to the molecular weight of air, and p a is the intake pressure, V c The maximum volume in the cylinder.

[0194] Exhaust purity refers to the ratio of the mass of air in the exhaust to the total mass of the exhaust gas.

[0195] Since no air is discharged in the first stage of the scavenging phase, the mathematical expression of the exhaust purity in the first stage is:

[0196] β n =0(3.1);

[0197] Since the exhaust components of the second stage of the scavenging phase are waste gas and mixed gas, the mathematical expression of the exhaust purity of the second stage is:

[0198]

[0199] Since the exhaust components of the third stage of the scavenging phase are mixed gas and air, the mathematical expression of the exhaust purity of the third stage is:

[0200]

[0201] In formula (3.1), formula (3.2) and formula (3.3), β n is the exhaust purity of the current step, b3 is the model characteristic coefficient that characterizes the exhaust rate of the mixed gas at a certain moment, is the instantaneous exhaust flow rate of the cylinder, m 1an is the mass of air in the mixing zone at the current step length, m 1bn is the mass of exhaust gas in the mixing zone at the current step length.

[0202] In step S4, the ventilation theoretical model includes one or more of a gas mass change theoretical model, a cylinder pressure change theoretical model, a gas temperature change theoretical model, a gas volume change theoretical model, and a ventilation process parameter theoretical model. It is understood that by substituting the mathematical expression of the model characteristic coefficient b1 of the instantaneous air mixing ratio, the mathematical expression of the model characteristic coefficient b2 of the instantaneous exhaust gas mixing ratio, and the mathematical expression of the model characteristic coefficient b3 representing the mixed gas exhaust rate at a certain moment into the mathematical expression of the gas mass change relationship, the mathematical expression of the cylinder pressure change, the mathematical expression of the gas temperature change relationship, the mathematical expression of the gas volume change relationship, and the mathematical expression of the ventilation process parameter, one or more of the gas mass change theoretical model, the cylinder pressure change theoretical model, the gas temperature change theoretical model, the gas volume change theoretical model, and the ventilation process parameter theoretical model can be obtained. Thus, the corresponding theoretical model can be directly used or combined with other models or data to predict the changes in the cylinder gas mass, pressure, temperature, volume, and ventilation process parameter, with high prediction speed and high prediction accuracy.

[0203] According to some embodiments of the present invention, the mathematical expression of the gas mass change relationship includes a mathematical expression of the total gas mass of the mixing zone in the first stage, the second stage, and the third stage, a mathematical expression of the air mass of the mixing zone, a mathematical expression of the exhaust gas mass of the mixing zone, a mathematical expression of the air mass of the air zone, and a mathematical expression of the exhaust gas mass of the exhaust zone; the mathematical expression of the ventilation process parameter includes a mathematical expression of the exhaust gas purity;

[0204] The variation relationship of the model characteristic coefficient of the instantaneous air mixing ratio and the variation relationship of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio are specifically obtained by combining the simulation variation process of each zone in each stage of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model with the mathematical expression of the total gas mass of the mixing zone in the first stage, the second stage, and the third stage, the mathematical expression of the air mass in the mixing zone, the mathematical expression of the exhaust gas mass in the mixing zone, the mathematical expression of the air mass in the air zone, and the mathematical expression of the exhaust gas mass in the exhaust zone;

[0205] The change relationship of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment is obtained by combining the simulation change process of each stage and each zone of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model with the mathematical expression of the cylinder instantaneous intake flow, cylinder instantaneous exhaust flow and exhaust purity.

[0206] According to some embodiments of the present invention, in step S3, determining the simulated change process of each zone in each stage of the simulated scavenging phase based on the calculation results of the three-dimensional simulation model includes using a component transport model in the ventilation flow simulation model to perform a simulation calculation process. Specifically, using the component transport model in the ventilation flow simulation model to perform the simulation calculation process includes the following sub-steps:

[0207] S301: Considering that the cylinder volume region mixed with very little fresh charge (air) is still close to the exhaust region, the average mass fraction of carbon dioxide in the simulated cylinder space at the beginning of the simulated scavenging phase is set as the initial mass fraction, the region in the simulated cylinder space where the carbon dioxide mass fraction is greater than 95%-100% of the initial mass fraction is defined as the simulated exhaust region, and the region in the simulated cylinder space where the carbon dioxide mass fraction is less than 100%-105% of the average carbon dioxide mass fraction of the air charged into the simulated cylinder space is defined as the simulated air region. The volumes of the simulated air region and the simulated exhaust region at any moment are calculated, and the region in the simulated cylinder space excluding the simulated exhaust region and the simulated air region is defined as the simulated mixing region;

[0208] S302: Calculating the gas masses of the simulated air zone and the simulated exhaust zone based on the volumes of the simulated air zone and the simulated exhaust zone at any moment. The volume of the simulated mixing zone is the total volume of the space in the simulated cylinder minus the volumes of the simulated air zone and the simulated exhaust zone. The mass of the simulated mixing zone is the total mass of the gas in the simulated cylinder minus the gas masses of the simulated air zone and the simulated exhaust zone.

[0209] S303: Starting from the simulated scavenging phase, a certain crankshaft angle is used as a calculation step, for example, 0.5 degree crankshaft angle is used as a calculation step, and a simulated change process is calculated.

[0210] It can be understood that the simulation change process includes the mass changes of the simulated mixing zone, the simulated exhaust zone and the simulated air zone, as well as the simulated exhaust purity, so that the change relationship of b1, b2 and b3 can be calculated. The simulation change process also includes the changes in the gas temperature of the simulated mixing zone, the air temperature of the simulated air zone and the exhaust temperature of the simulated exhaust zone in the first stage, the second stage and the third stage; the changes in the gas volume of the simulated mixing zone, the simulated air volume of the air zone and the exhaust volume of the simulated exhaust zone in the first stage, the second stage and the third stage; the changes in the simulated air supply ratio, the simulated charging efficiency and the simulated capture rate to verify the accuracy of the ventilation theoretical model obtained by the present invention in predicting the ventilation process.

[0211] According to some embodiments of the present invention, when the scavenging process begins, air immediately mixes with the exhaust gas upon entering the cylinder. Therefore, the value of b1 is relatively large in the initial scavenging phase, and changes slightly with the crankshaft angle. As air continues to enter the cylinder, the rate at which the air zone enters the mixing zone decreases rapidly. Therefore, based on the simulated change process, an exponential equation is used to fit the change in b1 throughout the scavenging phase. Therefore, in step S3, the mathematical expression for the model characteristic coefficient of the instantaneous air mixing ratio obtained through regression fitting is:

[0212]

[0213] In formula (4), τ is the normalized time of the scavenging phase, and ξ1 and k1 are constants.

[0214] The mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of exhaust gas is obtained through regression fitting, which includes the following steps: the exhaust gas from the exhaust zone entering the mixing zone is divided into the first sub-process and the second sub-process. Considering that in the first sub-process, the exhaust gas from the exhaust zone is entrained and infiltrated by the air jet filling the cylinder, so during the simulation change process, b2 increases parabolically at the beginning of the scavenging phase, but this increase process will end as the volume of the exhaust zone decreases; in the second sub-process, the exhaust gas from the exhaust zone mixes normally into the mixing zone, and b2 decreases exponentially. Therefore, based on the analysis and fitting of the calculation results of the three-dimensional simulation model, the following is obtained:

[0215]

[0216] In formula (5), τ g is the end time of the first sub-process, τ1 is the normalized time of the second sub-process, ξ2 and k2 are constants;

[0217] The mathematical expression of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment is obtained through regression fitting, including the following steps:

[0218] Considering that the change of exhaust gas components is continuous, the exhaust gas in the first stage of the scavenging stage is all waste gas. In the second stage, the proportion of mixed gas in the exhaust gas gradually increases. Therefore, b3 gradually increases from zero in the second stage of the scavenging process. According to the calculation results of the three-dimensional simulation model, the growth of b3 in the second stage is exponential; in the early stage of the third stage, the short circuit of air increases rapidly, the proportion of mixed gas in the exhaust gas decreases, and b3 decreases exponentially; in the late stage of the third stage, the exhaust gas purity slowly decreases in a linear relationship. According to the calculation results of the three-dimensional simulation model, b3 increases in a linear relationship. After the above analysis and fitting, we get:

[0219]

[0220] In formula (6), τ2 represents the normalized time of the second and third stages, τ3 represents the normalized time of the third stage, τ4 represents the normalized time of the late third stage, and τ β1 is the end time of the second stage, τ β2 is the end time of the early stage of the third stage; ξ3 and ξ4 are constants, and k3, k4 and k5 are constants.

[0221] like Figure 10 As shown, Figure 10 The figure shows a comparison between the curve drawn based on the mathematical expression of b1, b2 and b3 obtained by regression fitting and the curve of the change of b1, b2 and b3 obtained by the calculation result of the three-dimensional simulation model. Among them, the regression fitting determination coefficient R2 of b1, b2 and b3 are 0.963, 0.972 and 0.969 respectively, indicating that the fitting accuracy is good. The New Benson modified theoretical model obtained by the present invention no longer considers the change relationship between the model characteristic coefficient b1 of the instantaneous mixing ratio of air and the model characteristic coefficient b2 of the instantaneous mixing ratio of exhaust gas as a constant value or a simple linear change, but a suitable change relationship determined according to the characteristics of the ventilation process of the overhead valve two-stroke aviation heavy fuel oil engine. A new model characteristic coefficient b3 is introduced to characterize the proportion of the mixed gas in the exhaust gas at a certain moment, so that the New Benson modified theoretical model obtained by the present invention can capture the basic characteristics of the ventilation process of the overhead valve two-stroke aviation heavy fuel oil engine and reveal the mechanism of gas composition change. Compared with the New Benson model, it significantly improves the prediction accuracy of parameters such as capture rate, charging efficiency, and exhaust purity.

[0222] According to some embodiments of the present invention, the values ​​of ξ1, ξ2, ξ3 and ξ4 and the values ​​of k1 and k2 change with the operating conditions of the overhead valve two-stroke aviation heavy fuel oil engine. The values ​​of ξ1, ξ2, ξ3 and ξ4 and the values ​​of k1 and k2 are determined based on the simulation calculation results of the three-dimensional simulation model and the Gauss-Newton iteration method (wherein the Gauss-Newton iteration method is one of the least squares methods), so that the curve drawn according to the mathematical expressions of b1, b2 and b3 can be more closely aligned with the change curves of b1, b2 and b3 obtained from the calculation results of the three-dimensional simulation model, with smaller deviations, which is conducive to making the prediction accuracy of the ventilation theory model obtained by the present invention higher.

[0223] Throughout this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" indicate that the specific features, structures, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0224] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine, characterized in that: The steps include: S1: Establishing a New Benson correction model: Dividing the cylinder volume in the scavenging phase into an air zone, a mixing zone, and an exhaust zone, and dividing the scavenging phase into a first stage, a second stage, and a third stage, wherein the exhaust in the first stage is the exhaust gas in the exhaust zone; the exhaust in the second stage is the mixed gas in the mixing zone and the exhaust gas in the exhaust zone, and the proportion of the mixed gas in the exhaust in the second stage gradually increases, while the proportion of the exhaust gas gradually decreases; the exhaust in the third stage is the air in the air zone and the mixed gas in the mixing zone, and the proportion of the air in the exhaust in the third stage first increases and then decreases, while the proportion of the mixed gas first decreases and then increases; S2: Based on the New Benson correction model, a mathematical model describing the scavenging phase is determined, wherein the mathematical model includes a model characteristic coefficient for controlling the instantaneous mixing ratio of air from the air zone entering the mixing zone, a model characteristic coefficient for controlling the instantaneous mixing ratio of exhaust gas from the exhaust zone entering the mixing zone, and a model characteristic coefficient for characterizing the mixed gas exhaust rate at a certain moment. In step S2, the mathematical model includes a mathematical expression for the relationship between gas mass changes, a mathematical expression for the relationship between in-cylinder pressure changes, a mathematical expression for the relationship between gas temperature changes, a mathematical expression for the relationship between gas volume changes, and a mathematical expression for a gas exchange process parameter. S3: Determine the simulation change process of each stage and each zone in the simulated scavenging stage based on the calculation results of the three-dimensional simulation model, and combine the mathematical model to obtain the change relationship of the model characteristic coefficient of the instantaneous air mixing ratio, the change relationship of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio, and the change relationship of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment, and obtain the mathematical expression of the model characteristic coefficient of the instantaneous air mixing ratio, the mathematical expression of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio, and the mathematical expression of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment through regression fitting; S4: Combine the mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of the air, the mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of the exhaust gas, and the mathematical expression of the model characteristic coefficient representing the exhaust rate of the mixed gas at a certain moment into the mathematical model describing the scavenging stage to establish a ventilation theory model.

2. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 1, characterized in that: In step S4, the ventilation theoretical model includes one or more of a gas mass change theoretical model, a cylinder pressure change theoretical model, a gas temperature change theoretical model, a gas volume change theoretical model, and a ventilation process parameter theoretical model.

3. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 2, characterized in that: The mathematical expression of the gas mass change relationship includes a mathematical expression of the total gas mass of the mixing zone in the first stage, the second stage, and the third stage, a mathematical expression of the air mass of the mixing zone, a mathematical expression of the exhaust gas mass of the mixing zone, a mathematical expression of the air mass of the air zone, and a mathematical expression of the exhaust gas mass of the exhaust zone; The mathematical expressions of the ventilation process parameters include a mathematical expression of exhaust gas purity; The variation relationship of the model characteristic coefficient of the instantaneous air mixing ratio and the variation relationship of the model characteristic coefficient of the instantaneous exhaust gas mixing ratio are specifically obtained by combining the simulation variation process of each zone in each stage of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model with the mathematical expression of the total gas mass of the mixing zone in the first stage, the second stage, and the third stage, the mathematical expression of the air mass in the mixing zone, the mathematical expression of the exhaust gas mass in the mixing zone, the mathematical expression of the air mass in the air zone, and the mathematical expression of the exhaust gas mass in the exhaust zone; The change relationship of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment is obtained by combining the simulation change process of each stage and each zone of the simulated scavenging stage determined by the calculation results of the three-dimensional simulation model with the cylinder instantaneous intake flow, the cylinder instantaneous exhaust flow and the mathematical expression of the exhaust purity.

4. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 3, characterized in that: The mathematical expression of the gas temperature change relationship includes the mathematical expression of the gas temperature of the mixing zone in the first stage, the second stage and the third stage, the mathematical expression of the air temperature of the air zone and the mathematical expression of the exhaust gas temperature of the exhaust gas zone; the mathematical expression of the gas volume change relationship includes the mathematical expression of the gas volume of the mixing zone in the first stage, the second stage and the third stage, the mathematical expression of the air volume of the air zone and the mathematical expression of the exhaust gas volume of the exhaust gas zone.

5. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 4, characterized in that: The mathematical expressions of the ventilation process parameters also include a mathematical expression of the air supply ratio, a mathematical expression of the charging efficiency and a mathematical expression of the capture rate.

6. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 5, characterized in that: The mathematical expression of the air supply ratio is: In formula (1), l0 is the real-time air supply ratio, is the real-time total mass of air entering the cylinder per cycle, p a is the intake pressure, V c is the maximum volume in the cylinder, R is the ratio of the molar gas constant to the molecular weight of air, T a is the intake air temperature; The mathematical expression of the charging efficiency is: In formula (2), η c is the real-time inflation efficiency, T a is the intake air temperature, m 2n is the gas mass in the air zone at the current step length, m 1an is the mass of air in the mixing zone at the current step length, R is the ratio of the molar gas constant to the molecular weight of air, and p a is the intake pressure, V c is the maximum volume in the cylinder; The mathematical expression of the exhaust gas purity in the first stage is: β n ＝0(3.1)； The mathematical expression of the exhaust gas purity in the second stage is: The mathematical expression of the exhaust gas purity in the third stage is: In formula (3.1), formula (3.2) and formula (3.3), β n is the exhaust purity of the current step, b3 is the model characteristic coefficient that characterizes the exhaust rate of the mixed gas at a certain moment, is the instantaneous exhaust volume, m 1an is the mass of air in the mixing zone at the current step length, m 1bn is the mass of exhaust gas in the mixing zone at the current step length.

7. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to any one of claims 1 to 5, characterized in that: In step S3, determining the simulation change process of each stage and each zone of the simulated scavenging stage by the calculation result of the three-dimensional simulation model includes using the component transport model in the ventilation flow simulation model to perform a simulation calculation process.

8. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 7, characterized in that: The simulation calculation process using the component transport model in the ventilation flow simulation model specifically includes the following sub-steps: S301: setting the average mass fraction of carbon dioxide in the simulated cylinder space at the start of the simulated scavenging phase as the initial mass fraction, defining a region in the simulated cylinder space where the carbon dioxide mass fraction is greater than 95%-100% of the initial mass fraction as a simulated exhaust gas region, and defining a region in the simulated cylinder space where the carbon dioxide mass fraction is lower than 100%-105% of the average mass fraction of carbon dioxide in the air charged into the simulated cylinder space as a simulated air region, so as to calculate the volumes of the simulated air region and the simulated exhaust gas region at any moment, and defining the region of the simulated cylinder space excluding the simulated exhaust gas region and the simulated air region as a simulated mixing region; S302: Calculating the gas masses of the simulated air zone and the simulated exhaust zone based on the volumes of the simulated air zone and the simulated exhaust zone at any moment, wherein the volume of the simulated mixing zone is the total volume of the space in the simulated cylinder minus the volumes of the simulated air zone and the simulated exhaust zone, and the mass of the simulated mixing zone is the total mass of the gas in the space in the simulated cylinder minus the gas masses of the simulated air zone and the gas masses of the simulated exhaust zone; S303: Starting from the simulated scavenging phase, with a certain crankshaft angle as a calculation step, the simulated change process is calculated.

9. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 8, characterized in that: In step S3, the mathematical expression of the model characteristic coefficient of the instantaneous air mixing rate obtained by regression fitting is: In formula (4), b1 is the model characteristic coefficient of the instantaneous air mixing rate, τ is the normalized time of the scavenging stage, ξ1 and k1 are constants; The mathematical expression of the model characteristic coefficient of the instantaneous mixing rate of the exhaust gas obtained by regression fitting includes the following steps: dividing the exhaust gas from the exhaust zone entering the mixing zone into a first sub-process and a second sub-process, considering that in the first sub-process, the exhaust gas from the exhaust zone is entrained and infiltrated by the air jet charged into the cylinder, and in the second sub-process, the exhaust gas from the exhaust zone is normally mixed into the mixing zone, and the following is obtained by analysis and fitting: In formula (5), b2 is the model characteristic coefficient of the instantaneous mixing rate of the exhaust gas, τ g is the end time of the first sub-process, τ1 is the normalized time of the second sub-process, ξ2 and k2 are constants; The mathematical expression of the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment obtained by regression fitting includes the following steps: Considering that the change of exhaust gas components is continuous, the exhaust gas in the first stage of the scavenging stage is all waste gas. In the second stage, the proportion of the mixed gas in the exhaust gas gradually increases. In the early stage of the third stage, the short circuit of air increases rapidly, and the proportion of the mixed gas in the exhaust gas decreases. In the late stage of the third stage, the exhaust gas purity slowly decreases in a linear relationship. The analysis and fitting results are: In formula (6), b3 is the model characteristic coefficient representing the mixed gas exhaust rate at a certain moment, τ2 represents the normalized time of the second stage and the third stage, τ3 represents the normalized time of the third stage; τ4 is the normalized time of the late third stage, τ β1 is the end time of the second stage, τ β2 is the end time of the early stage of the third stage; ξ3 and ξ4 are constants, and k3, k4 and k5 are constants.

10. The method for establishing a theoretical model of ventilation for an overhead valve two-stroke aviation heavy fuel oil engine according to claim 9, characterized in that: The values ​​of ξ1, ξ2, ξ3 and ξ4, as well as the values ​​of k1 and k2 vary with the operating conditions of the overhead valve two-stroke aviation heavy fuel oil engine. The values ​​of ξ1, ξ2, ξ3 and ξ4, as well as the values ​​of k1 and k2 are determined based on the simulation calculation results of the three-dimensional simulation model and the Gauss-Newton iteration method.

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