Study On Macroscopic And Microscopic Spray Characteristics Of N-Butanol/Biodiesel

As the two major problems of the energy crisis and environmental pollution become increasingly prominent,new renewable alternatives of fuels have gradually attracted people's attention.Among them,Biodiesel,with its high cetane number and flash point,easy transportation and storage,low sulfur content,and the ability to reduce the emission of some pollutants,has gradually become a research hotspot in the field of alternative fuels.However,the high viscosity and density of biodiesel results in poor atomization quality.The atomization process of fuel directly affects the subsequent combustion and emission processes,so it is particularly important to improve the atomization quality of biodiesel.In this research,the physical and chemical properties of biodiesel were improved by adding different proportions of n-butanol.The stability of n-butanol/biodiesel was observed after the N10(10% by volume of n-butanol)and N20(20% by volume of n-butanol)was left standing,and the physicochemical properties of mixed fuel were tested and analyzed by experiments and empirical formulas,the results show that biodiesel and n-butanol can be mutually soluble,The addition of n-butanol can reduce density,viscosity,cetane number and low calorific value of biodiesel,but the latent heat of vaporization and oxygen content are increased.In this paper,matlab software was used to process the spray image.The main process was removing the background,image enhancement and edge extraction.In the image enhancement stage,the self-edited contrast linearly broadened program could be more suitable for the image processing in this research by comparing different image enhancement methods.The constant volume device,high-speed photography and the shadowing method was used to test and analyze the macroscopic spray characteristics including spray tip penetration,spray tip velocity,spray cone angle,spray volume and spray gas entrainment mass of B100,N10 and N20.The macroscopic spray characteristics under different injection pressure(30,45,60,75 MPa),nozzle diameter(0.20,0.25,0.30 mm)and back pressure(1,2,3 MPa)was explored.The results show that the spray tip penetration and spray tip velocity of N10 and N20 are less than B100,and the spray cone angle,spray volume and spray gas entrainment mass are greater than B100,indicating that after the addition of n-butanol to biodiesel,the spray shape gradually expands radially and effect of atomization is improved.With an increase of injection pressure and nozzle diameter,spray tip penetration,spray tip velocity,spray cone angle,spray volume and spray gas entrainment mass of n-butanol/biodiesel mixed fuel have been increased,the fuel and air are mixed better;With an increase in back pressure,spray tip penetration,spray tip velocity,and spray volume are significantly reduced,and the spray cone angle is increased;The spray gas entrainment mass under back pressure of 2 MPa and 3 MPa is higher than 1 MPa,and the trend of spray gas entrainment mass rising alternately.The phase doppler particle analyzer(PDPA)measurement system combined with a constant volume device which was used to test and analyze the microscopic spray characteristics including sauter mean diameter(SMD),characteristic diameter and particle size distribution of B100,N10 and N20.The microscopic spray characteristics under different injection pressure(30,45,60,75 MPa)?nozzle diameter(0.20,0.25,0.30 mm)and back pressure(1,2,3 MPa)were explored,the results show that the SMD size of these three fuels is N20 <N10 <B100,the characteristic diameter also shows the same trend.In the cumulative volume distribution,the slope of curve of N20 is the largest,followed by N10,and the slope of curve of B100 is the smallest,indicating that after the addition of n-butanol,the number of small-size oil droplets has increased,and the atomization effect was improved.As the proportion of n-butanol increases,this phenomenon becomes more pronounced.With an increase of injection pressure,the SMD and characteristic diameter of the n-butanol/biodiesel mixed fuel gradually decreased,and the cumulative volume distribution curve of mixed fuel began to move in the direction of smaller particle size.Higher the injection pressure,greater will be the slope of cumulative volume distribution curve.With the increase of the nozzle diameter and back pressure,the SMD and characteristic diameter of the n-butanol/biodiesel mixed fuel increased significantly.The cumulative volume distribution curve of the mixed fuel gradually moved toward the larger particle size,and the slope of curve became smaller and smaller,which indicates that the atomization effect is poor when nozzle diameter and back pressure are large.Based on the microscopic spray characteristics,this research uses gray correlation analysis to evaluate the four influencing factors(n-butanol blending ratio,injection pressure,nozzle diameter,and back pressure)affecting the SMD,and the priority that affects the size of SMD is determined as follows: back pressure> nozzle diameter> injection pressure> n-butanol blending ratio.