Method for predicting evaporation behavior of mixed fuel in hydrogen / nitrogen mixed atmosphere

Abstract

The invention discloses a mixed fuel evaporation behavior prediction method in a hydrogen / nitrogen mixed atmosphere, and belongs to the field of clean fuel phase change mechanisms. Comprising the steps of 1, initializing a simulation domain and a physical field; step 2, reading a whole-field initial liquid phase volume fraction, and judging whether a grid unit is a gas-liquid interface or not; if the interface is a gas-liquid interface, entering the step 3; if not, entering the step 4; 3, updating the droplet mass evaporation rate, and describing interface movement caused by droplet evaporation; 4, calculating the speed of a non-interface grid unit, and solving a mass and momentum conservation equation; step 5, performing liquid phase volume fraction to obtain the liquid phase volume fraction, the component mass fraction and the temperature of the full-field grid unit; step 6, updating the physical properties of pure components and the mixture; 7, judging whether the calculation time is up or not, and if yes, ending; and if so, repeating the steps 2-7. The method is suitable for mixed fuel with obvious component polarity difference in a multi-component liquid phase, and the problem of interface fuzziness caused by extra convection flux at an interface due to the large density ratio of the gas phase and the liquid phase in evaporation is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of engine fuel spray, and relates to a method for predicting evaporation behavior of mixed fuel in a hydrogen / nitrogen mixed atmosphere. BACKGROUND

[0002] The premixed quality of the oil-gas mixture directly determines the combustion efficiency and emissions of the engine, and the key to the formation of the mixture lies in the evaporation process of fuel droplets [YI P, JIA M, LONG W, et al. Evaporation of pure and blended droplets of diesel and alcohols (C2-C9) under diesel engine conditions[J]. Numerical Heat Transfer, Part A: Applications, 2017, 71(3): 311-326.]. When alcohol-based fuel is mixed with hydrogen, on the one hand, the differences in thermodynamic and transport properties between alcohol and alkanes in alcohol-based fuel lead to significant temperature and component concentration gradients inside the droplet [YUAN B, ZHAO H, HUANG Y, et al. Investigation on cold start issues of methanol engines and its improvement from the perspective of droplet evaporation[J]. Fuel, 2025, 380: 133249.]. On the other hand, hydrogen has higher thermal conductivity, lower density and viscosity, which will lead to significantly higher fuel evaporation quality and heat transfer rate than air [CERNAT A, PANA C, NEGURESCU N, et al. The Influence of Hydrogen on Vaporization, Mixture Formation and Combustion of Diesel Fuel at an Automotive Diesel Engine[J]. Sustainability, 2020, 13(1): 202.]. It can be seen that the evaporation behavior of alcohol-based fuel in a hydrogen-containing atmosphere is completely different from that in a traditional nitrogen or exhaust gas atmosphere, and the research on the phase change mechanism of complex multi-component droplets in a hydrogen-containing atmosphere is not perfect.

[0003] The current single droplet evaporation model generally uses the ideal vapor-liquid equilibrium model (Raoult's law) [Sazhin S S, Shchepakina E, Sobolev V A, et al. Puffing / micro-explosion in composite multi-component droplets [J]. International Journal of Heat and Mass Transfer, 2022, 184: 122210.][Wang X, Li C, Wang X, et al. Effect of volatility differences in binary mixture droplet components on evaporation dynamics [J / OL]. Physics of Fluids, 2024, 36(12) [2025-07-20]. https: / / pubs.aip.org / pof / article / 36 / 12 / 123377 / 3327016 / Effect-of-volatility-differences-in-binary-mixture.], and ignores the Stefan flow [Vlasov V A. On a theory of mass transfer during the evaporation of aspherical droplet [J]. International Journal of Heat and Mass Transfer, 2021, 178: 121597.]. This assumption is reasonable when calculating the evaporation of single-component droplets in low-temperature environments. However, for the case of methanol fuel and hydrogen double injection, the polarity difference between methanol and alkane molecules is large, and the real bubble point temperature deviates significantly from the ideal situation. Hydrogen will also enhance the heat and mass transfer on the droplet surface. Therefore, it is necessary to consider the non-ideal vapor-liquid equilibrium and Stefan flow to more accurately reveal the evaporation mechanism of alcohol-based fuel and hydrogen mixed injection. Therefore, by studying the influence of hydrogen concentration and alcohol ratio on the evaporation characteristics of mixed fuel, the invention comprehensively analyzes the droplet normalized surface area, droplet internal temperature and components, etc. Evaporation characteristics, and proposes a mixed fuel evaporation behavior prediction method under hydrogen / nitrogen mixed atmosphere, laying a foundation for improving the combustion efficiency of alcohol-based fuel-hydrogen double injection engines. SUMMARY

[0004] In view of the problems in the prior art, the application provides a mixed fuel evaporation behavior prediction method in a hydrogen / nitrogen mixed atmosphere, the improved evaporation model prediction liquid drop normalized surface area has good consistency with the experimental measurement results, the evaporation mechanism of alcohol-based fuel in the hydrogen / nitrogen mixed atmosphere is revealed, the influence of the fuel component ratio on the liquid drop evaporation performance is analyzed, and reference is provided for optimizing the hydrogen and alcohol-based fuel double-injection fuel ratio strategy.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is:

[0006] A mixed fuel evaporation behavior prediction method in a hydrogen / nitrogen mixed atmosphere, the prediction method comprises the following steps:

[0007] Step 1, initialize the simulation domain and the physical field.

[0008] Considering that the evaporation of a spherical liquid drop has symmetry, in order to improve efficiency, the application adopts two-dimensional simulation. The calculation domain range, the liquid drop size and the initial position are set based on the Cartesian coordinate system, the calculation domain is divided by using a structured grid, and the calculation domain is discretized into a plurality of grid units. The initial temperature of the liquid drop, the environment temperature, the environment pressure, the liquid drop composition and the environment gas composition are set. The simulation calculation time is set.

[0009] Step 2: based on the calculation domain and the physical field of step 1, read the initial liquid phase volume fraction of the whole field , the definition formula is , wherein is the liquid volume in a grid unit, is the volume of a grid unit. And judge whether the grid unit is a gas-liquid interface. If it is a gas-liquid interface, that is , then step 3 is entered. If it is not a gas-liquid interface, it is directly jumped to step 4.

[0010] Step 3: on the grid unit corresponding to the gas-liquid interface identified in step 2, the mass evaporation rate of the liquid drop is updated by using the non-ideal vapor-liquid equilibrium interface boundary condition, and the more accurate geostrophic velocity of the gas-liquid interface is obtained by using the double-pressure velocity coupling method, so as to avoid the interference of interface deformation caused by Stefan flow and accurately describe the interface movement caused by liquid drop evaporation. Specifically:

[0011] Step 3.1: the mass evaporation rate of the liquid drop is updated by using the non-ideal vapor-liquid equilibrium interface boundary condition:

[0012] (1)

[0013] , wherein represents the mass evaporation rate of the liquid drop of component ; represents the total mass evaporation rate; is the gas phase density; is the gas phase mole fraction of component ; is the interface normal vector; is the gas phase mass fraction of component ; is the gas phase mole fraction of component on the interface, calculated according to the vapor-liquid equilibrium model: , is the relative molecular mass of component ; is the gas phase mole fraction of component on the interface, calculated according to the vapor-liquid equilibrium model:

[0014] (2)

[0015] wherein, is the ambient pressure; is the liquid phase mole fraction of component on the interface; is the saturated vapor pressure of component at the interface temperature ; is the activity coefficient of component , calculated by the UNIFAC activity coefficient model, which can accurately describe the thermodynamic non-ideal behavior of mixtures caused by significant polarity difference, and has the advantages of simple model and faster calculation speed.

[0016] Further, the activity coefficient is composed of a combination part and a residual part :

[0017] (3)

[0018] (4)

[0019] (5)

[0020] In the formula, the subscripts and represent components; and are the molecular normalized van der Waals volume and surface area; specifically: represents the molecular normalized van der Waals volume of component ; represents the molecular normalized van der Waals volume of component ; represents the molecular normalized van der Waals volume of component ;the liquid molar fraction of component denotes the component the molecular normalized van der Waals surface area of component denotes the component the molecular normalized van der Waals surface area of component denotes the component the total number of groups in the molecule of component denotes the group is the component the number of groups in the molecule of component and are the residual activity coefficients of the groups of the mixture and the pure component respectively, both calculated analogously, specifically:

[0021] the residual activity coefficient of the group is calculated as:

[0022] (6)

[0023] wherein is the surface fraction of the group is the surface fraction of the group denotes the weight factor of the group acting in the local environment of the group when . denotes the weight factor of the group acting in the local environment of the group denotes the weight factor of the group acting in the local environment of the group denotes the number of groups occurring in the vicinity of the group denotes the number of groups occurring in the vicinity of the group is the surface area of the normalized group

[0024] the residual activity coefficient of the group is calculated as:

[0025] (7)

[0026] wherein ​​​​​​​The surface fraction of group m in pure component The surface fraction of group n in pure component The surface fraction of group m in pure component The surface fraction of group n in pure component

[0027] Step 3.2: Based on the droplet mass evaporation rate obtained in step 3.1, the interface grid cell velocity during droplet evaporation is calculated.

[0028] Numerically, the Stefan flow effect caused by evaporation will cause the velocity field to be discontinuous at the interface, affecting the numerical stability and the accuracy of interface identification. To solve this problem, the invention uses a double pressure velocity coupling method to solve the interface motion, decoupling the velocity caused by Stefan flow and the advection velocity of the gas-liquid interface. The specific method is as follows:

[0029] First, the volume expansion term on the right side of the mass conservation equation is introduced into the nearest pure gas phase grid, and a set of mass and momentum conservation equations containing Stefan flow velocity are solved, and the specific formula is as follows:

[0030] (8)

[0031] (9)

[0032] Where the right side of the continuity equation shown in formula (8) is the mass exchange source term on the gas-liquid interface; is the liquid phase density; is the velocity vector; is the directional vector; is the interface function, and represent a small area element and a volume element, respectively. In the momentum equation shown in formula (9), represents time; is the mixed average density of gas and liquid phases; is the dynamic viscosity; is the unit tensor; is the gravitational acceleration; is the surface tension, , is the surface tension coefficient at the interface, is the curvature. According to the above formula, the velocity containing Stefan flow .

[0033] Then, keeping the same discrete conditions and boundary conditions, a set of mass and momentum conservation equations without Stefan flow expansion terms are solved for the whole field, and the specific formula is as follows:

[0034] (10)

[0035] (11)

[0036] The velocity of non-interface grid cell is calculated .

[0037] The velocity is used to solve the subsequent scalar field transport equations, and the velocity is used to perform the interface translation. Through the coupling of the two, the continuity and stability of the interface velocity field can be effectively guaranteed, and the non-physical deformation of the interface caused by Stefan flow can be prevented. Finally, the interface grid cell velocity is obtained.

[0038] Step 4: If it is not a gas-liquid interface, the non-interface grid cell velocity is calculated, and the following mass and momentum conservation equations are solved:

[0039] (12)

[0040] (13)

[0041] The velocity of non-interface grid cell is calculated .

[0042] Step 5: Based on the velocity obtained in step 3 or step 4, where the velocity of the liquid phase region is marked as , and the velocity of the gas phase region is marked as , the scalar field transport equations such as the liquid volume fraction, component transport equation and energy equation are solved. The liquid volume fraction transport equation is:

[0043] (14)

[0044] The gas and liquid component transport equations are as follows:

[0045] (15)

[0046] (16)

[0047] where represents the density of component in the gas phase; represents the mass fraction of component in the gas phase; represents a small volume element of the gas phase; represents a small area element of the gas phase; represents the interface velocity; represents the mass diffusion coefficient of component in the gas phase; represents the gradient operator; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase; ρl represents the density of the liquid phase.

[0048] The energy equation of the final gas phase and the liquid phase is:

[0049] (17)

[0050] (18)

[0051] wherein, ρg represents the density of the gas phase; cp,g represents the specific heat capacity at constant pressure of the gas phase mixture; Tg represents the temperature of the gas phase; kg represents the thermal conductivity of the gas phase; ρl represents the density of the liquid phase; cp,l represents the specific heat capacity at constant pressure of the liquid phase mixture; Tl represents the temperature of the liquid phase; kl represents the thermal conductivity of the liquid phase.

[0052] According to the above equations, the liquid phase volume fraction, the component mass fraction and the temperature of the full-field grid unit are finally obtained.

[0053] Step 6: The temperature field and the mass fraction field of each component are obtained based on the calculation results of step 5, and the pure component and the mixture property are updated. The property change formula of the substance is derived from the property library provided by the National Institute of Standards and Technology (NIST is a commonly used property library in the field). It includes: viscosity, density, thermal conductivity, specific heat capacity at constant pressure, ideal gas specific heat capacity, latent heat of vaporization and saturated vapor pressure.

[0054] Step 7: It is judged whether the simulation calculation time is reached, if the simulation calculation time is exceeded, the calculation is ended. If the simulation calculation time is less than the simulation calculation time, the steps 2-7 are cycled.

[0055] The beneficial effects of the present application are:

[0056] The application develops an improved evaporation model considering Stefan flow and coupling non-ideal vapor-liquid equilibrium model, which is used to study the evaporation mechanism of isooctane / methanol two-component droplet in hydrogen / nitrogen mixed atmosphere. The UNIFAC non-ideal vapor-liquid equilibrium interface condition is adopted, which can accurately describe the mass fraction of each component on the droplet surface, so as to obtain more accurate evaporation rate, effectively solve the thermodynamic non-ideal behavior of alkanes and alcohol components in alcohol-based fuel due to the significant difference in polarity, and better quantify the evaporation driving force. At the same time, by adopting the double-pressure velocity coupling method, the interface shrinkage velocity caused by evaporation and the additional velocity vector caused by Stefan flow are decoupled, which can avoid the non-physical interface deformation caused by Stefan flow and effectively sharpen the interface. The improved evaporation model developed by the application has good consistency with the experimental measurement results of the normalized surface area of the droplet, and provides a more accurate method for studying the evaporation of mixed component droplets in complex gas atmosphere. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 The flowchart of the application is shown in the figure;

[0058] Figure 2 The schematic diagram of the calculation domain is shown in the figure;

[0059] Figure 3 The bubble point temperature of the isooctane and methanol mixed system of the ideal and non-ideal vapor-liquid equilibrium model is shown in the figure;

[0060] Figure 4 The velocity comparison with and without considering Stefan flow is shown in the figure;

[0061] Figure 5 The evolution of isooctane mass fraction (a) and temperature (b) inside the droplet with normalized distance at different times is shown in the figure;

[0062] Figure 6 The comparison of the simulation results and experimental results of the normalized surface area of the droplet is shown in the figure;

[0063] Figure 7 The evolution of the normalized surface area and surface temperature of the droplet with time is shown in the figure. DETAILED DESCRIPTION

[0064] The application will be further described below in combination with specific implementation cases.

[0065] The embodiment provides a method for predicting the evaporation behavior of mixed fuel in a nitrogen / hydrogen mixed atmosphere, as shown in the figure, the prediction method comprises the following steps: Figure 1

[0066] ​Step 1, initialization of simulation domain and physical field. Considering the symmetry of spherical droplet evaporation, the present invention adopts two-dimensional simulation to improve efficiency. The calculation domain range is set based on the Cartesian coordinate system, a square calculation domain with a side length of and a droplet size of 10 and an initial position at the center of the calculation domain, see Figure 2 . A structured grid is used for partitioning in the calculation domain, which discretizes the calculation domain into multiple grid cells. The initial temperature of the droplet is set to 298K, the environmental temperature is 473K, the environmental pressure is 0.56MPa, the droplet is composed of isooctane with a volume fraction of 0.15 and methanol with a volume fraction of 0.85. The environmental gas is composed of hydrogen with a volume fraction of 0.07455 and nitrogen with a volume fraction of 0.92545. The simulation calculation time is set to 1.17ms.

[0067] Step 2: Based on the calculation domain and physical field of step 1, read the initial liquid phase volume fraction of the whole field , the definition is , where is the liquid volume in a grid cell, is the volume of a grid cell. And determine whether the grid cell is a gas-liquid interface. If it is a gas-liquid interface, i.e. , then go to step 3, if it is not a gas-liquid interface, then directly jump to step 4.

[0068] Step 3: On the grid cell corresponding to the gas-liquid interface identified in step 2, update the droplet mass evaporation rate using the non-ideal vapor-liquid equilibrium interface boundary condition, and use the double pressure velocity coupling method to obtain more accurate geostrophic velocity of the gas-liquid interface, avoid the interference of Stefan flow caused by interface deformation, and accurately describe the interface movement caused by droplet evaporation. Specifically:

[0069] Step 3.1: Update the droplet mass evaporation rate using the non-ideal vapor-liquid equilibrium interface boundary condition as shown in equations (1)-(7);

[0070] Step 3.2: Based on the droplet mass evaporation rate obtained in step 3.1, calculate the interface grid cell velocity during droplet evaporation.

[0071] In numerical calculation, the Stefan flow effect caused by evaporation will cause the velocity field to be discontinuous at the interface, affecting the numerical stability and the accuracy of interface identification. In order to solve this problem, the present invention uses a double pressure velocity coupling method to solve the interface movement, which decouples the velocity caused by Stefan flow and the geostrophic velocity of the gas-liquid interface. The specific method is:

[0072] First, the volume expansion term on the right side of the mass conservation equation is introduced into the nearest pure gas grid, and a set of mass and momentum conservation equations containing Stefan flow velocity are solved, as shown in equations (8) and (9).

[0073] Then, keeping the same discrete conditions and boundary conditions, a set of mass and momentum conservation equations without the Stefan flow expansion term are solved for the whole field, as shown in equations (10) and (11), to calculate the velocity without Stefan flow .

[0074] The velocity is used for subsequent scalar field transport equation solving, and the velocity is used for interface translation. Through the coupling of the two, the continuity and stability of the interface velocity field can be effectively guaranteed, and the non-physical deformation of the interface caused by Stefan flow can be prevented. Finally, the interface grid cell velocity is obtained.

[0075] Step 4: If it is not a gas-liquid interface, calculate the non-interface grid cell velocity, solve the mass and momentum conservation equations as shown in equations (12) and (13), and calculate the velocity of the non-interface grid cell .

[0076] Step 5: Based on the velocity obtained in step 3 or step 4, where the velocity of the liquid phase region is marked as , and the velocity of the gas phase region is marked as , the scalar field transport equations such as liquid volume fraction, component transport equation and energy equation are solved. The liquid volume fraction transport equation is shown in equation (14);

[0077] The gas and liquid component transport equations are shown in equations (15) and (16);

[0078] The final energy equations of the gas and liquid phases are shown in equations (17) and (18);

[0079] According to the above equations, the liquid volume fraction, component mass fraction and temperature of the grid cell in the whole field are finally obtained.

[0080] Step 6: Based on the calculation results of step 5, the temperature field and the mass fraction field of each component are obtained, and the pure component and mixture properties are updated. The property change formula of the substance is derived from the property library provided by the National Institute of Standards and Technology (NIST, which is commonly used in the field of property library). It includes: viscosity, density, thermal conductivity, constant-pressure specific heat capacity, ideal gas specific heat capacity, latent heat of vaporization and saturated vapor pressure.

[0081] Step 7: Determine if the simulation calculation time has been reached. If it has been exceeded, the calculation ends. If it has been less than the simulation calculation time, repeat steps 2-7.

[0082] Model validation:

[0083] An improved evaporation model, based on the steps above and considering Stefan flow coupled with a non-ideal vapor-liquid equilibrium model, was established to simulate the evaporation process of a mixture of n-heptane and n-decane in a nitrogen and oxygen atmosphere and compared with experimental results [DAÏF A, BOUAZIZ M, CHESNEAU X, et al. Comparison of multicomponent fuel dropletvaporization experiments in forced convection with the Sirignano model[J].Experimental Thermal and Fluid Science, 1998, 18(4): 282-290.]. Specifically, the droplet diameter was 1.36 mm and the temperature was 290 K. The ambient temperature was 297 K and the pressure was 0.1 MPa. The ambient gas consisted of 78% nitrogen and 22% oxygen (by volume). The normalized surface area decay analysis of the droplets yielded the following results: Figure 6 As shown, the simulation and experimental data are in good agreement, demonstrating the reliability and accuracy of the improved evaporation model established in this invention.

[0084] Calculation results are displayed:

[0085] according to Figure 7 The evolution of droplet normalized surface area and surface temperature over time revealed that droplet evaporation can be divided into three stages: expansion stage (0-0.072ms), during which the droplet normalized surface area continuously increases and the droplet temperature rises rapidly; the enhanced molecular thermal motion inside the droplet leads to a decrease in density, which in turn triggers the droplet volume expansion effect; at 0.072ms, the droplet normalized surface area reaches a peak of 1.278; transition stage (0.072ms-0.3ms), as heating continues, the increase in droplet surface temperature tends to level off, and the droplet normalized surface area decreases; (3) stable evaporation stage: after 0.3ms, the rate of decrease in droplet normalized surface area is basically stable; the rate of heat absorption by droplet surface evaporation and the rate of heat transfer from the environment to the droplet reach a dynamic equilibrium.

[0086] The embodiments described above are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere, characterized in that, The prediction method includes the following steps: Step 1: Initialize the simulation domain and physical fields; Set the initial temperature of the droplet, the ambient temperature, the ambient pressure, the droplet composition, the ambient gas composition, and the simulation calculation time; Step 2: Based on the computational domain and physical field of Step 1, read the initial liquid volume fraction for the entire field. Its defining formula is ,in It is the volume of liquid within a grid cell. It is the volume of a grid cell; and it determines whether the grid cell is a gas-liquid interface; if it is a gas-liquid interface, then... If the gas-liquid interface is not present, proceed to step 3; otherwise, skip directly to step 4. Step 3: On the grid cells corresponding to the gas-liquid interface identified in Step 2, the droplet mass evaporation rate is updated using the interface boundary conditions of non-ideal vapor-liquid equilibrium, and a dual pressure-velocity coupling method is used to obtain a more accurate advection velocity of the gas-liquid interface, avoiding interface deformation interference caused by Stefan flow, and accurately describing the interface motion caused by droplet evaporation. Step 4: If it is not a gas-liquid interface, calculate the velocity of the non-interface mesh elements and solve the mass and momentum conservation equations; Step 5: Based on the velocity obtained in Step 3 or Step 4, solve the scalar field transport equations such as liquid volume fraction, component transport equation, and energy equation to finally obtain the liquid volume fraction, component mass fraction, and temperature of the entire field grid cell. Step 6: Based on the calculation results of Step 5, obtain the temperature field and the mass fraction field of each component, and update the physical properties of the pure component and the mixture; Step 7: Determine if the simulation calculation time has been reached. If it exceeds the simulation calculation time, the calculation ends; if it is less than the simulation calculation time, repeat steps 2-7.

2. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 1, characterized in that, Step 1 specifically includes: A two-dimensional simulation was adopted, with the computational domain, droplet size, and initial position set based on the Cartesian coordinate system. The computational domain was discretized into multiple grid cells using a structured grid. The initial temperature of the droplet, ambient temperature, ambient pressure, droplet composition, ambient gas composition, and simulation time were also set.

3. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 1, characterized in that, Step 3 specifically includes: Step 3.1: Update the droplet mass evaporation rate using non-ideal vapor-liquid equilibrium interfacial boundary conditions: （1）； in, Indicates components The droplet mass evaporation rate; Indicates the total mass evaporation rate; This refers to the gas phase density. Components in the gas phase The mass diffusion coefficient; Represents the interface normal vector; Components The mass fraction of the gas phase; Components on the interface The mass fraction of the gas phase, , Components The relative molecular mass, Components on the interface The gas phase mole fraction is calculated based on the vapor-liquid equilibrium model: （2）； in, Due to environmental pressures; Components on the interface The liquid phase mole fraction; Components At interface temperature The saturated vapor pressure below; Components The activity coefficient is calculated using the UNIFAC activity coefficient model; Step 3.2: Based on the droplet mass evaporation rate obtained in Step 3.1, calculate the velocity of the interface mesh elements during the droplet evaporation process; A dual-pressure-velocity coupling method is employed to solve the interface motion, decoupling the velocity induced by the Stefan flow from the advection velocity at the gas-liquid interface; specifically: First, the volume expansion term on the right-hand side of the mass conservation equation is introduced into the nearest pure gas phase grid to solve a set of mass and momentum conservation equations containing Stefan flow velocities. The specific formulas are as follows: （8）； （9）； Among them, the right side of the continuity equation shown in formula (8) is the mass exchange source term at the gas-liquid interface; The density of the liquid phase; It is a velocity vector; It is the direction vector; For interface functions, and Let represent the infinitesimal area element and volume element, respectively; in the momentum equation shown in formula (9), Indicates time; The average density of the gas-liquid two-phase mixture; Dynamic viscosity; Unit tensor; It is the acceleration due to gravity; For surface tension, , It is the surface tension coefficient at the interface. The curvature is used to calculate the velocity containing the Stefan flow using the above formula. ; Then, keeping the same discrete and boundary conditions, we solve a set of mass and momentum conservation equations for the entire field without Stefan flow expansion terms. The specific formulas are as follows: （10）； （11）； The velocity without Stefan flow was calculated. ; Using speed To solve the subsequent scalar field transport equations, velocity is used. Perform interface translation; ultimately obtain the interface grid unit speed.

4. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 1, characterized in that, In step 3.1, the activity coefficient Combination part and the remaining parts composition: （3）； （4）； （5）； In the formula, Indicates components Molecular normalized van der Waals volume; Indicates components Molecular normalized van der Waals volume; Indicates components The liquid phase mole fraction; Indicates components Molecular normalized van der Waals surface area; Indicates components Molecular normalized van der Waals surface area; addition symbol Indicates components The total number of groups in the molecule, Indicates a group; It is a component Groups in molecules The number; and They are mixtures and pure components, respectively. group The residual activity coefficient.

5. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 1, characterized in that, In step 3.1: The The calculation formula is: （6）； in, as a group The face value; as a group The face value; Indicates a group In groups The weighting factors that take effect in the local environment, and when hour, Indicates a group In groups Weighting factors that take effect in the local environment; Indicates a group In groups Weighting factors that take effect in the local environment; in the summation symbol Table group The number of surrounding groups, Indicates a group The number of surrounding radicals; Normalized groups Surface area; The The calculation formula is: （7）； in, Pure components The face fraction of the group 𝑚 in the middle. Pure components The face fraction of group n in the matrix.

6. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 5, characterized in that, In step 4, the equations for the conservation of mass and momentum are: （12） （13）； The velocity of the non-interface mesh element was calculated. .

7. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 6, characterized in that, In step 5: The liquid phase volume fraction transport equation is: （14）； The transport equations for gas and liquid phase components are as follows: （15） （16）； in, Indicates components in the gas phase The density; Indicates components in the gas phase The mass fraction; Represents a small volume element in the gas phase; Represents a small area element in the gas phase; Indicates interface speed; Indicates components in the gas phase The mass diffusion coefficient; Represents the gradient operator; Indicates the components in the liquid phase The density; Indicates the components in the liquid phase The mass fraction; Represents a small volume element in the liquid phase; Represents a small area element in the liquid phase; Indicates the components in the liquid phase The mass diffusion coefficient; The final energy equations for the gas and liquid phases are: （17）； （18）； in, Indicates the density of the gas phase; This represents the specific heat capacity at constant pressure of a gas-phase mixture; Indicates the gas phase temperature; Indicates the thermal conductivity of the gas phase; Indicates the density of the liquid phase; This represents the specific heat capacity at constant pressure of a liquid mixture; Indicates the gas phase temperature; Indicates the thermal conductivity of the liquid phase; Based on the above equations, the liquid phase volume fraction, component mass fraction, and temperature of the entire field grid cells are finally obtained.

8. The method for predicting the evaporation behavior of mixed fuels in a hydrogen / nitrogen mixed atmosphere according to claim 7, characterized in that, In step 6, the changes in the physical properties of the substance include: viscosity, density, thermal conductivity, specific heat capacity at constant pressure, specific heat capacity of an ideal gas, latent heat of vaporization, and saturated vapor pressure.

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