Experimental Investigation Of Liquid Viscosity And Surface Tension For Fatty Acid Esters And Their Mixtures With N-alkane By Surface Light Scattering Method

The use of fossil fuels to generate a large number of pollutants is the main factor of the current haze pollution in China,and it has gradually become one of the main factors restricting China’s economic and social development.Therefore,improving fuel quality and exploring new clean fuels have been widely recognized at home and abroad as an important means of controlling pollution from the source.Biodiesel is an oxygen-containing fuel.The main component of biodiesel is fatty acid esters,which can be obtained through esterification from raw materials such as animal,vegetable,and catering fuels.Biodiesel can be used directly as a fuel to replace or blend with fossil diesel,which can effectively reduce the emissions of pollutants such as SO_x and particulate matter produced by combustion.In connection with the design and optimization of the internal combustion engine(ICE)injection system,the viscosity,surface tension,and density of biodiesel are basic thermophysical data that determine the atomization performance of the fuel,which in turn affects the combustion efficiency and emissions of the ICE.At the same time,considering the complex composition of actual biodiesel and petrochemical diesel,in order to effectively characterize the thermophysical properties of various possible mixed fuels,it is necessary to propose and study model fuels that can replace complex biofuel mixed systems.Therefore,the surface light scattering method was used to study the viscosity and surface tension of twelve representative fatty acid methyl/ethyl esters(FAMEs/FAEEs),and their corresponding correlation models were established based on experimental data.Binary mixed model fuels of n-dodecane and methyl butyrate/methyl decanoate,n-decane and ethyl decanoate/ethyl dodecanoate were proposed and their viscosity,surface tension and density were studied.On the basis of the experimental data,correlation model of these physical properties was proposed as the function of temperature and mole fraction.A large number of experimental data and corresponding models obtained in this paper can provide basic data for the design and optimization of internal combustion engine injection systems.The main research results obtained in this paper are as follows:(1)In order to study the physical parameters of the fuel in the high temperature region,the surface light scattering experimental system was improved,and the test temperature range was extended to 573 K.The reliability of the experimental system was verified with reference materials such as n-dodecane,ethanol.The influences of liquid density,vapor density,vapor viscosity and other factors on the uncertainty of measurement results were investigated.The viscosity and surface tension measurement uncertainty of this system were 2%(k=2)and 1%(k=2).(2)Using an improved surface light scattering experimental system,the viscosity and surface tension of twelve FAMEs/FAEEs under saturated conditions were studied at a temperature range of(298～448)K,including 6FAMEs:methyl butyrate,methyl heptanoate,methyl octanoate,methyl decanoate,methyl laurate,methyl myristate;6 FAEEs:ethyl hexanoate,ethyl heptanoate,ethyl octanoate,ethyl decanoate,ethyl dodecanoate,ethyl myristate.The viscosity data were correlated as the reciprocal temperature-dependent polynomial equations,which the relative percentage deviations of experimental data from those calculated by the corresponding equation were within±1%.The surface tension data obtained from the SLS experiment were fitted to the van der Waals type,the relative percentage deviations of experimental data from those calculated by the corresponding equation were within±1%for both properties.(3)The liquid density of binary mixtures of n-dodecane with methyl butyrate/decanoate,n-decane with ethyl decanoate/dodecanoate was determined by an Anton Paar U-tube densimeter between(293 and 423)K,(293～433)K at a 10 K increments,respectively.Each system contains three ratios,where the mole fractions of n-dodecane and n-decane are 0.2500,0.5000,and 0.7500,respectively.On the basis of the experimental data,the corresponding correlation of temperature and mole fraction was fitted.The deviations between experimental data and those values calculated by correlation are within the range of±0.5%.(4)The model fuels of binary mixtures of n-dodecane with methyl butyrate/decanoate,n-decane with ethyl decanoate/dodecanoate were proposed.The liquid viscosity,surface tension of binary mixtures were measured by the SLS with the temperature range of(308～413)K、(313～423)K,respectively,close to saturation conditions.Each system contains three ratios,where the mole fractions of n-dodecane and n-decane are 0.2500,0.5000,and 0.7500,respectively.A total of 111 points of viscosity and surface tension experimental data points were obtained.The blanks of viscosity and surface tension experimental data of the above-mentioned binary mixtures of alkane and fatty acid ester binary systems were filled.Based on the data obtained from experiments,the liquid viscosity and surface tension correlations against temperature and mole fraction were formed.For all systems,the relative deviations between the experimental data of viscosity and surface tension and the corresponding correlation models are±2%and±1%,respectively,which can meet the general engineering calculation needs.