Comparative Study On Spray And Combustion Characteristics Of Petrochemical Diesel,F-T Diesel And Biodiesel

The use of clean alternative fuels for internal combustion engines can save petroleum resources and reduce pollutant emissions.Coal-based F-T diesel has the advantages of high cetane number,good evaporation and low aromatic hydrocarbon content,which is a promising alternative fuel for diesel;however,F-T diesel has low viscosity and poor lubricity,which will aggravate the wear of diesel injection pumps and injectors in long-term use.Biodiesel has the advantages of wide source of raw materials,clean and renewable,and its higher viscosity and good lubricity.Blending F-T diesel with biodiesel can achieve complementary advantages and has good application potential.In this paper,0 # petrochemical diesel(D100),coal-based F-T diesel oil(FT100),biodiesel(BD100),and F-T diesel/biodiesel blends with biodiesel blending ratios of 20%(FB20)and 50%(FB50)were used as test fuels.Based on the constant volume combustion chamber test system,the effects of ambient temperature and injection pressure on the spray and combustion characteristics of D100,FT100 and BD100 were studied by highspeed camera method.Secondly,the spray and combustion characteristics of D100,FT100,BD100,FB20 and FB50 were compared and analyzed to investigate the effects of fuel properties and biodiesel blending ratio on the above parameters.By studying the spray characteristics of D100,FT100 and BD100 under different ambient temperatures and injection pressures,it is found that:(1)Increasing the ambient temperature is conducive to the atomization and evaporation of fuel droplets.Compared with 300 K ambient temperature,at 773 K,the maximum liquid spray penetration distance of D100,FT100 and BD100 is reduced by 41.8%,54.9% and 29.1% respectively,the average liquid spray cone angle is reduced by 32.4%,38.4% and 34.5%,and the maximum liquid spray area is reduced by 83.3%90.3%、72.4%。(2)Increasing the injection pressure increases the kinetic energy of the fuel beam and also promotes the evaporation of fuel droplets.Compared with 100 MPa injection pressure,at 140 MPa,the average liquid spray cone angle and the maximum liquid spray area of D100 and FT100 slightly decrease;due to higher density and viscosity,the maximum liquid spray penetration distance and the maximum liquid spray area of BD100 increased by 7.8% and7.9%,respectively.By studying the combustion characteristics of D100,FT100,and BD100 under different ambient temperatures and injection pressures,it is found that:(1)Increasing ambient temperature promotes the chemical reaction of combustion,and the fuel ignition position is closer to the nozzle.Compared to the ambient temperature of 800 K,at 850 K,the ignition delay of D100,FT100,and BD100 are shortened by 20.2%,30.5%,and 29.6%,respectively.The flame lift-off length are shortened by 14.4%,16.0%,and 22.2%,respectively.The peak flame area increased by 25.4%,29.5%,and 60.2%,respectively.The total flame luminosity increased by 100.1%,47.3%,and 66.2%,respectively.(2)Compared with the injection pressure of100 MPa,the ignition delay of D100,FT100,and BD100 at 140 MPa are shortened by 14.3%,12.5%,and 12.5%,respectively.The flame lift-off length increased by 6.5%,5.7%,and 7.1%,respectively,and the peak flame area increased by 41.3%,23.1%,and 23.9%,respectively.Comparing the spray characteristics and combustion characteristics of D100,FT100,BD100,FB20 and FB50,it can be found that:(1)Compared with D100,the maximum liquid phase spray penetration distance and maximum liquid phase spray area of FT100 decreased by21.2% and 40.3%,respectively,and the maximum liquid phase spray penetration distance and maximum liquid phase spray area of BD100 increased by 22.2% and 39.1% respectively.With the increase of biodiesel blending ratio,the atomization evaporation of the blended fuel became worse.Compared with FT100,the maximum liquid phase spray penetration distance of FB20 and FB50 increased by 10.6% and 29.8%,and the maximum liquid phase spray area increased by 28.9% and 64.9%,respectively.(2)Compared with D100,due to the high cetane number,the ignition of FT100 and BD100 are shortened by 22.5% and 5.0% respectively,and the flame lift-off length are shortened by 15.6% and 6.8%,respectively;compared with D100,the peak flame area of FT100 increased by 16.5%,while BD100 decreased by 7.6%;due to the inhibition of soot formation by FT100 and BD100,and the further promotion of soot oxidation by BD100 due to its high oxygen content,the total flame luminosity of both decreased by 25.3% and 51.2%respectively,and the total KL factor decreased by 6.3% and 47.4%,respectively.With the increase of biodiesel blending ratio,the cetane number of the blended fuel decreased and the oxygen content increased.Compared with FT100,the ignition delay of FB20 and FB50 increases by 3.2% and 16.1%,the flame lift-off length increases by 2.1% and 6.3% respectively,the total flame luminosity of the flame decreases by 3.2% and 9.7% respectively,and the total KL factor decreases by 7.4% and 20.2%,respectively.