Experimental And Molecular Dynamics Simulation Study On Density Of Fatty Acid Methyl Ester,Ethyl Ester And Their Mixtures With N-dodecane

In recent years,China's economy has developed rapidly and people's quality of life has increased substantially.However,the increasingly prominent environmental pollution problems,especially haze,have also received widespread attention.The exhaust from motor vehicles is the main source of fine particles in smog,especially for diesel vehicles.Therefore,improving fuel quality,especially diesel quality,and developingnew types of environmentally friendly fuels are important means of controlling pollution.Biodiesel is a new type of fuel with good environmental characteristics.The thermophysical properties of biodiesel,especially density,have an important impact on atomization performance in internal combustion engines,as well as subsequent combustion efficiencies and emissions of pollutants and fine particulate matter.Therefore,experimental and theoretical studies on the density of biodiesel or its medium and short-chain fatty acid methyl esters,ethyl esters and their mixtures with n-dodecane play an important role as a model fuel in internal combustion engines and in the design of fuel injection systems for internal combustion engines.This thesis is mainly divided into two parts,one part is the experimental study on the density of fatty acid methyl ester,ethyl ester and their mixtures with n-dodecane,and the other part is the molecular dynamics simulation study of the corresponding system.In terms of density experiments,the densities of methyl butyrate,methyl hexanoate,methyl decanoate,methyl decanoate,methyl laurate,methyl myristate,methyl palmitate,ethyl hexanoate,ethyl heptanoate,ethyl octanoate,ethyl decanoate,ethyl laurate,ethyl palmitate,ethyl myristate,and n-dodecane were measured by vibrating tube method.The densities of the binary mixture systems of methyl decanoate,methyl decanoate,methyl laurate and n-dodecane were also measured.The temperature range was 293.15 K-473.15 K and the ratio of n-dodecane in the mixture x₁ was 0.1-0.9.The excess molar volumes of the binary mixture systems and the relative deviations between the experimental and calculated values of the pure qualities were calculated by using the obtained density data.In terms of molecular dynamics simulation,the molecular dynamics simulations of methyl decanoate and n-dodecane systems were carried out under AMBER96,CHARMM27,OPLS-AA and GROMOS-UA force fields to obtain optimized force fields for the systems.Taking n-hexane as an example,the effects of simulated step number,time step and particle number on density accuracy were studied.The densities of mixed systems of methyl decanoate with n-dodecane,methyl laurate with n-dodecane were calculated by using AMBER 96 force field.The main conclusions of this thesis are as follows.?1?The densities of methyl butyrate,methyl hexanoate,methyl decanoate,methyl decanoate,methyl laurate,methyl myristate,methyl palmitate,ethyl hexanoate,ethyl heptanoate,ethyl octanoate,ethyl decanoate,ethyl laurate,ethyl palmitate,ethyl myristate,and n-dodecane were obtained.The densities of the binary mixture systems of methyl decanoate,methyl decanoate,methyl laurate and n-dodecane were also obtained.?2?The excess molar volumes of the binary mixtures and the relative deviations between experimental and calculated values of the pure qualities were obtained.?3?The above systems were simulated by molecular dynamics.Taking methyl decanoate and dodecane system as an example,the effects of four different force fields on density accuracy were studied.The optimized force fields were AMBER96 and OPLA-AA force fields.?4?Taking n-hexane as an example,the effects of simulated step number,time step and particle number on density simulation accuracy were studied,and the optimized parameters of n-hexane were obtained.?5?Using the AMBER96 force field to calculate the densities of methyl decanoate and n-dodecane,methyl laurate and n-dodecane,the relative deviations between experimental and simulated values were within4%,which can meet the needs of the project.