Research method for exploring combustion suppression mechanism of R1233zd (E) on R1270 based on reaction molecular dynamics

Abstract

The invention discloses a research method for exploring a R1233zd (E) to R1270 combustion suppression mechanism based on reaction molecular dynamics, which comprises the following specific steps of: constructing a topological structure of R1233zd (E) and R1270 single molecules by using Packmole software, carrying out structure optimization on the molecular topological structure, then constructing a mixed working medium oxygenolysis calculation cube unit, carrying out constant-volume constant-temperature calculation, and finally constructing a mixed working medium oxygenolysis calculation cube unit. In the calculation process, an instruction file in, a force field file and a model file need to be input, a dump of a molecular moving trajectory and a molecular bond energy information bond file are obtained according to a calculation result, atom bond breaking and bonding trajectories are observed by using ovito software, and change curves of reactants, products and molecular fragments in the bond file are extracted. According to the method, the oxidation pyrolysis process of the R1233zd (E) / R1270 mixed working medium is simulated by using a ReaxFFMD method, a change curve of reactants and products along with time is extracted through ChemTraYzer, the inhibition theory of the R1233zd (E) on the hydrocarbon working medium combustion process is observed from the atomic level, and bonding and breaking behaviors between atoms which cannot be detected by experiments are made up.

Description

Technical Field

[0001] This study covers the cross-simulation research in the fields of refrigeration and computational chemistry, and involves a research method for exploring the flame inhibition mechanism of R1233zd(E) on R1270 based on reactive molecular dynamics. Background Art

[0002] The current research focus is on the development of new refrigerants with low GWP values. Hydrocarbons, hydrofluoroolefins, and hydrochlorofluorocarbons are highly potential alternative solutions. Most low-GWP alternative refrigerants are flammable, so the flammability issue has become a key concern during the refrigerant replacement process.

[0003] An inert and environmentally friendly working fluid is added to the hydrocarbon flammable working fluid to form an environmentally friendly mixed working fluid. The mixed working fluid not only overcomes the defects of pure hydrocarbon working fluids being flammable and explosive, but also has significantly improved thermodynamic properties compared with pure substances. R1270 is the most potential natural working fluid. However, its flammable performance limits its wide promotion and application. R1233zd(E) belongs to the fourth-generation environmentally friendly working fluid, and it is a high-performance working fluid without flammability problems among the fourth-generation working fluids. Some studies have shown that the thermodynamic properties of R1233zd(E) are significantly better than those of R245fa. Therefore, R1233zd(E) is an ideal alternative refrigerant. Ju et al. studied the environmentally friendly azeotropic mixtures composed of R1233zd(E) and four hydrocarbon refrigerants to replace the traditional R22 and R134a in heat pump water heaters. The research results show that R1233zd(E) / R1270 is a suitable substitute for R22 and R134a. When the mass fraction of R1233zd(E) / R1270 is 16% / 84%, its coefficient of performance COP is 2.13% and 10.14% higher than that of R22 and R134a respectively. The thermodynamic properties of the R1233zd(E) / R1270 mixed working fluid are better than those of traditional commercial refrigerants, and it is a new generation of high-performance and potentially applicable alternative refrigerant.

[0004] Although R1233zd(E) can narrow the flammable range of R1270, when the mixed refrigerant leaks to a certain concentration, it still has a certain degree of danger. Therefore, understanding the flammability limits and flame inhibition mechanisms of the R1233zd(E) / R1270 mixed refrigerant is the key to promoting the replacement of environmentally friendly refrigerants. It is very easy to understand the inhibition phenomenon of R1233zd(E) on the flammability limit of R1270 through experiments. However, it is difficult to obtain the microscopic inhibition mechanism of R1233zd(E) on the combustion characteristics of R1270 through experimental measurements. The combustion phenomena of multi-component gas mixtures are extremely complex, involving a large number of chemical reactions occurring within the picosecond to sub-picosecond level, making it almost impossible to capture experimentally. Traditional numerical methods usually require specific numerical conditions to complete partial calculations. Therefore, it is still challenging to understand the flame inhibition theory of R1233zd(E) on R1270 at the atomic level. The present invention proposes a method for exploring the flame inhibition mechanism of R1233zd(E) on R1270 using the reactive molecular dynamics theory. Summary of the Invention

[0005] The object of the present invention is to explore the influence of R1233zd(E) on the combustion mechanism of R1270 from the molecular and atomic perspectives using reactive molecular dynamics technology, and to solve the problem of the defect that the mesoscopic scale research method cannot analyze complex combustion phenomena from the microscopic level of bond breaking and bond formation.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] The present invention discloses a research method for exploring the flame inhibition mechanism of R1233zd(E) on R1270 based on reactive molecular dynamics, and its specific steps are as follows:

[0008] S1: Use the Packmole software to construct the topological structures of single molecules of R1233zd(E) and R1270 and optimize the molecular topological structures, and then construct a cubic unit for the oxidative decomposition calculation of the mixed refrigerant;

[0009] S2. Use density functional theory (DFT) to calculate the bonds, angles, dihedral angles and compare the results with those of ReaxFFMD calculations, and select the force field parameters applicable to the R1233zd(E) / R1270 mixed refrigerant;

[0010] S3. Use the Large-scale Atomic / Molecular Massively Parallel Simulator to perform constant-volume and constant-temperature calculations on the cubic unit established in S1. During the calculation process, an instruction file (in file), a force field file and a model file need to be input. The calculation results are the dump of the molecular running trajectory and the bond file of the molecular bond energy information. Use the Ovito software to observe the atomic bond-breaking and bond-forming trajectories;

[0011] S4. Use ChemTraYzer code to perform data post-processing, which includes but is not limited to: extracting the change curves of reactants, products and molecular fragments in the bond file, and analyzing the effects of different concentrations of R1233zd(E) on the oxidation process of R1270.

[0012] Preferably, the molecular formula of R1233zd(E) in step S1 is CF3CH=CHCl, and the molecular formula of R1270 is CH2=CHCH3; 5 cubic calculation units are constructed, and the oxidation inhibition mechanism of R1233zd(E) at different concentrations on R1270 is explored by adjusting the ratio of R1233zd(E) to R1270 in the simulation system.

[0013] Preferably, the density functional theory calculation described in step S2 adopts the B3LYP method and the 6-311G basis set for calculation. The research method based on the reaction molecular dynamics to explore the flame retardancy mechanism of R1233zd(E) on R1270 organic working fluid mainly includes the construction of single molecule topology construction, the construction of calculation cube unit model, the verification of force field parameters, the input of calculation in file and data post-processing. The bond dissociation energy curves of C1-C3 double bond, C3-C5 single bond, C5-F7 bond, C2-Cl9 bond and C1-H2 bond are compared. The lowest points of the bond dissociation energy curves coincide with each other, and the same change trend indicates that the reaction force field is suitable for the R1233zd(E) / R1270 system.

[0014] Preferably, the force field file in step S3 is the parameter file verified in S2. The model file is in the cubic unit file format established in S1. The stable volume constant temperature calculation adopts the standard NVT coefficient, that is, at a constant volume (V) and a constant temperature (T), the number of atoms (N) in the system remains unchanged.

[0015] Preferably, the construction of molecular topology is not limited to one construction technology, and existing mature commercial software such as MaterialStudio, Avogadro, Packmole, Gaussion, etc. can be used. Molecular topology optimization is based on the optimization technology provided by existing commercial software, such as the Dmol3 module provided by MaterialStudio. The molecular topology of R1233zd (E) and R1270 conforms to the basic chemical structure rules (see data or related website https: / / webbook.nist.gov).

[0016] Preferably, the method for constructing the computational cube unit is not limited to one method, and existing mature technologies such as software like MaterialStudio and Packmole can be used. Refer to Table 1 for calculating the number of molecules and molecular density within the cube. Five cases described in the present invention are given in Table 1. By controlling the density change in the cases, the pressure of the five cases is ensured to be constant. By changing the ratio of R1233zd(E) / R1270, the influence of different concentrations of R1233zd(E) on the complex combustion phenomenon of R1270 is explored.

[0017] Preferably, the purpose of validating the force field parameters is to select the force field parameter file applicable to the R1233zd(E) / R1270 mixed system. The validation method is to modify the bond length of the bond to be validated in the molecule on the basis of optimizing the molecular topology. Rigid scans are performed on models with different bond lengths using the b3lyp / 6-31g(d) basis set. Save the calculated energy of the molecular model after the rigid scan. Subsequently, convert the molecular models with different bond lengths into corresponding data files for ReaxFFMD calculations. Save the ReaxFFMD calculation results. Compare the density functional calculation results with the ReaxFFMD calculation results. When the lowest points of the curves coincide and the change trends are the same, it is considered reasonable.

[0018] Preferably, the computational instruction file in file does not have a fixed format. The in file is written based on the computational requirements. The in file calculation of the present invention usually adopts the standard NVT ensemble and the Nosé-Hoover heat bath method. The temperature damping parameter is set to 100 fs. Periodic boundary conditions are applied to the model in three directions. The integration algorithm used to advance the equations of motion is the Verlet algorithm. The bond order cutoff value for molecular recognition is set to 0.3. The computational cases of the present invention use the conjugate gradient algorithm to minimize the energy of the system.

[0019] Preferably, the data post-processing is not limited to one method. The purpose of data post-processing is to extract and visualize the process of bond breaking and bond formation between atoms. Perform data post-processing on the dump file or bond file of the calculation results. The code for data post-processing is not limited to one type. There are many relatively mature post-processing software codes at present. For example, open-source codes include ChemicalTrajectoryAnalyzer (ChemTraYzer), ReacNetGenerator, ovito, etc.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention uses the ReaxFF MD method to simulate the oxidative pyrolysis process of the R1233zd(E) / R1270 mixed refrigerant. The variation curves of reactants and products with time are extracted by ChemTraYzer. The inhibition theory of R1233zd(E) on the combustion process of hydrocarbon refrigerants is observed at the atomic level. It makes up for the bonding and bond-breaking behaviors between atoms that cannot be detected by experiments. Brief Description of the Drawings

[0022] The present invention will be further described below in conjunction with the drawings;

[0023] Figure 1 It is a simulation cube model diagram of the oxidation model of R1270 (a) and the oxidation model of R1233zd(E) / R1270 (b);

[0024] Figure 2 It is the molecular topological structure diagram of trans-1-chloro-3,3,3-trifluoropropene (R1233zd(E));

[0025] Figure 3 It is the bond dissociation energy diagram of the carbon-carbon double bond;

[0026] Figure 4 It is the bond dissociation energy diagram of the carbon-carbon single bond;

[0027] Figure 5 It is the bond dissociation energy diagram of the carbon-fluorine single bond;

[0028] Figure 6 It is the bond dissociation energy diagram of the carbon-chlorine single bond;

[0029] Figure 7 It is the bond dissociation energy diagram of the carbon-hydrogen single bond;

[0030] Figure 8 It is the oxidation decomposition curve diagram of R1270 under the inhibition of different concentrations of R1233zd(E);

[0031] Figure 9 It is the combustion inhibition reaction path diagram of R1233zd(E) on R1270 under fuel-rich conditions. Detailed Embodiment

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Refer to Figures 1 to 9, the present invention discloses a research method for exploring the flame inhibition mechanism of R1233zd(E) on R1270 based on reactive molecular dynamics, and the specific steps are as follows:

[0034] S1: Use Packmole software to construct the topological structures of single molecules of R1233zd(E) and R1270 and optimize the molecular topological structures. Subsequently, construct a computational cubic unit for the oxidative decomposition of the mixed working fluid. The molecular formula of R1233zd(E) is CF3CH=CHCl, and the molecular formula of R1270 is CH2=CHCH3; construct 5 cubic computational units, and explore the oxidation inhibition mechanism of R1270 by different concentrations of R1233zd(E) by adjusting the ratio of R1233zd(E) to R1270 in the simulation system. The construction method of the computational cubic unit is not limited to one method, and various existing mature technologies can be used, such as software like MaterialStudio and Packmole. Refer to Table 1 for the number and molecular density of molecules in the computational cube. Table 1 presents the 5 cases described in the present invention. Ensure that the pressure of the 5 cases remains unchanged by controlling the change in density in the cases. Explore the influence of different concentrations of R1233zd(E) on the complex combustion phenomenon of R1270 by changing the ratio of R1233zd(E) / R1270.

[0035] S2. Use density functional theory DFT to calculate the bonds, angles, and dihedral angles and compare with the results of ReaxFFMD calculations to select the force field parameters applicable to the R1233zd(E) / R1270 mixed working fluid. The density functional theory calculation uses the B3LYP method and the 6-311G basis set for calculation. The research method for exploring the flame inhibition mechanism of R1233zd(E) on the R1270 organic working fluid based on reactive molecular dynamics mainly includes the construction of single-molecule topology, the construction of a computational cubic unit model, the verification of force field parameters, the input of the calculation in file, and data post-processing. Compare the bond dissociation energy curves of the C1-C3 double bond, C3-C5 single bond, C5-F7 bond, C2-Cl9 bond, and C1-H2 bond. The coincidence of the lowest points of the bond dissociation energy curves and the same change trend indicate that the reaction force field is applicable to the R1233zd(E) / R1270 system. The purpose of force field parameter verification is to optimize the force field parameter file applicable to the R1233zd(E) / R1270 mixed system. The verification method is to modify the bond length of the bond to be verified in the molecule on the basis of optimizing the molecular topology. Use the b3lyp / 6-31g(d) basis set to perform a rigid scan on models with different bond lengths. Save the calculated energy of the molecular models after the rigid scan. Subsequently, convert the molecular models with different bond lengths into corresponding data files for ReaxFFMD calculations. Save the ReaxFFMD calculation results. Compare the density functional calculation results with the ReaxFFMD calculation results. When the lowest points of the curves coincide and the change trends are the same, it is reasonable.

[0036] S3. Use a large-scale atomic / molecular parallel simulator to perform constant volume and constant temperature calculations on the cubic unit established in S1. The calculation results obtain the dump of the molecular trajectory and the bond file of molecular bond energy information. Use ovito software to observe the atomic bond breaking and bonding trajectories. The constant volume and constant temperature calculation adopts the standard NVT system, that is, at a constant volume (V) and a constant temperature (T), the number of atoms (N) in the system remains unchanged. The construction of molecular topology is not limited to one construction technology, and existing mature commercial software such as MaterialStudio, Avogadro, Packmole, Gaussion, etc. can be used. Molecular topology optimization is based on the optimization technology provided by existing commercial software, such as the Dmol3 module provided by MaterialStudio. The molecular topology of R1233zd (E) and R1270 conforms to the basic chemical structure rules (see data or related websites https: / / webbook.nist.gov).

[0037] S4. The ChemTraYzer code was used to extract the change curves of reactants, products and molecular fragments in the bond file, and the effects of different concentrations of R1233zd(E) on the oxidation process of R1270 were analyzed.

[0038] The calculation instruction file in file has no fixed format and is written based on the calculation requirements. The in file calculation of the present invention usually adopts a standard NVT system and the Nosé-Hoover heat bath method. The temperature damping parameter is set to 100fs. The model applies periodic boundary conditions in three directions. The integral algorithm used to advance the equation of motion is the Verlet algorithm. The bond order cutoff value of molecular recognition is set to 0.3, and the calculation case of the present invention uses the conjugate gradient algorithm to minimize the energy of the system.

[0039] Data post-processing is not limited to one method. The purpose of data post-processing is to extract and visualize the bond breaking and bonding process between atoms, and to perform data post-processing on the dump file or bond file of the calculation results. Data post-processing codes are not limited to one type. Currently, there are many mature post-processing software codes. For example, open source codes include Chemical Trajectory Analyzer (ChemTraYzer), ReacNet Generator, ovito, etc.

[0040] In specific implementation, first, the oxidation system model is constructed using Packmole software. In the simulation system, the number of molecules of R1270 is 100, and the equimolar ratio is selected to be 1.2. The parameter α represents the ratio of the number of molecules of R1233zd(E) to the number of molecules of R1270. In this study, by controlling the molecular density in the simulation cube and adjusting the value of α, the effect of the concentration of R1233zd(E) on the oxidation process of R1270 is studied. As shown in Table 1, the density of all five simulation conditions is 0.1 g / cm 3 . As the number of molecules in the cube increases, its side length increases accordingly. Figure 1 is the simulation calculation model of R1270 and the R1270 / R1233zd(E) mixed system.

[0041] Table 1. Initial parameters of the simulation system

[0042]

[0043] Secondly, for the screening of the force field volume applicable to R1233zd(E), the density functional theory is used to calculate the bond dissociation energies of C-C, C=C, C-H, C-F, and C-C bonds in R1233zd(E). And the calculation results are compared with the ReaxFFMD calculation results. If they match well, it is confirmed that the force field parameters are applicable to the R1233zd(E) / R1270 simulation system. First, the molecular model of R1233zd(E) is constructed, and then the model is optimized. On the basis of the optimized model, the bond lengths of the bonds to be verified in the molecule are modified, and the rigid scans of the models with different bond lengths are performed using the b3lyp / 6—31g(d) basis set. The calculated energies of the molecular models after the rigid scans are saved. Subsequently, the molecular models with different bond lengths are converted into corresponding data files for ReaxFFMD calculations. The ReaxFFMD calculation results are saved. The density functional calculation results are compared with the ReaxFFMD calculation results. The calculation results are as Figure 2 shown.

[0044] Then, when using a large-scale atomic / molecular massively parallel simulator for calculations, three files need to be input, namely the instruction file (in file), the model file (data file), and the force field parameter file. The model visualized in Table 1 was converted into a data file. The CHOSFClN-2014 force field parameters verified in Step 2 were adopted. The calculations were usually carried out using the standard NVT ensemble, that is, at a constant volume (V) and a constant temperature (T), the number of atoms (N) in the system remained unchanged. To maintain a constant temperature, the Nosé-Hoover heat bath method was adopted. The temperature damping parameter was set to 100 fs. Periodic boundary conditions were applied in all three directions of the model. The integration algorithm used to advance the equations of motion was the Verlet algorithm. The cutoff value of the bond order for molecular recognition was set to 0.3. In this study, the conjugate gradient algorithm was used to minimize the energy of the system. Subsequently, the system was subjected to a 50-ps NVT equilibration simulation at 298.15 K, which matched the actual experimental temperature. Finally, 3000-ps NVT simulations were carried out at different temperatures.

[0045] Finally, the output species file, molecular atom trajectory dump file, and bond file were post-processed using ChemTraYzercode to count the number of molecules of reactants and products. The dump file was imported into the Ovito software to form a visualization interface for the oxidative decomposition process of the R1233zd(E) / R1270 mixed working fluid, and the effects of Cl and F radicals generated by the decomposition of R1233zd(E) on the oxidative decomposition process of R1270 were extracted. The calculation results are as Figure 2 and Figure 3 shown.

[0046] The above formulas are all data obtained by collecting a large amount of data for software simulation, and a formula close to the true value is selected. The coefficients in the formula are set by those skilled in the art according to the actual situation. The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics, characterized in that, The following steps are involved: S1: Use Packmole software to construct the topological structure of R1233zd(E) and R1270 single molecules and optimize the molecular topological structure, and then construct the mixed working fluid oxidation decomposition calculation cube unit; S2. Use density functional theory DFT to calculate bonds, angles, and dihedral angles and compare them with ReaxFFMD calculation results to select force field parameters suitable for R1233zd(E) / R1270 mixed working fluid; S3. Use a large-scale atomic / molecular parallel simulator to perform constant volume and constant temperature calculations on the cubic unit established in S1. The calculation process requires the input of the command file in file, the force field file and the model file. The calculation results obtain the dump file of the molecular trajectory and the molecular bond energy information bond file. Use the ovito software to observe the atomic bond breaking and bonding trajectories. S4. The ChemTraYzer code was used for data post-processing, which included but was not limited to extracting the change curves of reactants, products and molecular fragments in the bond file, and analyzing the effects of different concentrations of R1233zd(E) on the oxidation process of R1270.

2. The research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics according to claim 1, characterized in that, The molecular formula of R1233zd(E) described in step S1 is CF3CH=CHCl, and the molecular formula of R1270 is CH2=CHCH3; 5 cubic calculation units are constructed, and the oxidation inhibition mechanism of R1233zd(E) of different concentrations on R1270 is explored by adjusting the ratio of R1233zd(E) to R1270 in the simulation system.

3. The research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics according to claim 1, characterized in that, The density functional theory calculation described in step S2 uses the B3LYP method and the 6-311G basis set to perform the calculation, and compares the bond dissociation energy curves of the C1-C3 double bond, C3-C5 single bond, C5-F7 bond, C2-Cl9 bond, and C1-H2 bond. The lowest points of the bond dissociation energy curves coincide with each other, and the same change trend indicates that the reaction force field is suitable for the R1233zd(E) / R1270 system.

4. The research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics according to claim 1, characterized in that, The force field file in step S3 is the parameter file verified in S2, the model file is the cubic unit file format established in S1, and the constant volume and constant temperature calculation adopts the standard NVT ensemble, that is, at a constant volume (V) and a constant temperature (T), the number of atoms (N) in the system remains unchanged.

5. The research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics according to claim 1, wherein The construction of the molecular topology in step S1 uses the existing mature MaterialStudio, Avogadro, Packmole, and Gaussion software, and the optimization of the molecular topology is based on the optimization technology provided by the existing software.

6. The research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics according to claim 5, wherein The method for constructing the computational cube unit uses a variety of existing mature technologies, such as MaterialStudio and Packmole software, to calculate the number and molecular density of molecules in the cube, and to ensure that the pressure of the analysis case remains unchanged by controlling the change in density in the case. By changing the ratio of R1233zd(E) / R1270, the influence of different concentrations of R1233zd(E) on the complex combustion phenomenon of R1270 is explored.

7. The research method for exploring the flame inhibition mechanism of R1270 by R1233zd(E) based on reactive molecular dynamics according to claim 1, characterized in that The verification of the force field parameters in step S2 is applicable to the force field parameter file of the R1233zd(E) / R1270 mixed system. The verification method is to modify the bond length of the bond to be verified in the molecule on the basis of optimizing the molecular topology structure, perform a rigid scan on the models with different bond lengths using the b3 lyp / 6-31g(d) basis set, save the calculated energy of the molecular models after the rigid scan, then convert the molecular models with different bond lengths into corresponding data files for ReaxFFMD calculation, save the ReaxFFMD calculation results, and compare the density functional calculation results with the ReaxFFMD calculation results.

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