Study On Spray Characteristics Of Diesel-Biodiesel-DBE Blended Fuels

Biodiesel is a fatty acid methyl ester or ethyl ester produced by the esterification or transesterification of plant oils,animal oils(including waste oils)or microbial oils with methanol or ethanol.It is usually used as an additive to the conventional fossil diesel.However,the spray characteristics of diesel-biodiesel blended fuels are poor due to the higher density,viscosity and surface tension of biodiesel,which will have a negative effect on the combustion and emission characteristics of the engine.In order to solve the above problems,di-n-butyl ether(DBE)was blended into the diesel-biodiesel blended fuel.And this paper aims to improve their spray characteristics.The spray characteristics of five fuels,the neat diesel(D100),80%diesel+20%biodiesel(D80B20),72%diesel+18%biodiesel+10%di-n-butyl ether(D72B18DBE10),64%diesel+16%biodiesel+20%di-n-butyl ether(D64B16DBE20)and 56%diesel+14%biodiesel+30%di-n-butyl ether(D56B14DBE30),under various injection and ambient pressures were investigated experimentally in this paper.Various injection pressures(60 MPa,70 MPa,80 MPa,90 MPa,and 100 MPa)were obtained by using the high-pressure common-rail fuel injection system.Various ambient pressures(1 MPa,2 MPa,and 3 MPa)were obtained by using the high-pressure nitrogen bottle and the constant volume chamber.The spray process was recorded by using the high-speed schlieren photographic system,and the spray image was processed by using the image-processing program developed by ourselves.Based on experimental data,effects of the fuel blending ratio,injection pressure and ambient pressure on the spray tip penetration,spray cone angle and spray projected area were studied.Based on empirical equations,the Sauter mean diameter of spray droplets and the fuel-air equivalent ratio distribution of five fuels were obtained.The experimental results of five fuels showed that D80B20 had the longest spray tip penetration,the largest Sauter mean diameter and fuel-air equivalence ratio at the same axial position or radial position,and the smallest spray cone angle and spray projected area.With the DBE volume fraction increasing,the spray tip penetration decreased slightly,and Sauter mean diameter and fuel-air equivalence ratio at the same axial position or radial position decreased,while the spray cone angle and spray projected area increased.D64B16DBE20 had the closest macroscopic spray characteristics to diesel.And blending a certain proportion of DBE can improve the spray characteristics of diesel-biodiesel blended fuels,thereby promoting the mixing of fuel with surrounding gas.With the injection pressure increasing,the spray tip penetration and spray projected area of D64B16DBE20 increased,and the spray cone angle and fuel-air equivalent ratio distribution were less influenced.With the ambient pressure increasing,the spray tip penetration,spray projected area and fuel-air equivalent ratio at the same axial position or radial position decreased,while the spray cone angle increased.