Study On Spray And Combustion Characteristics Of F-T Diesel Blending Oxygenated Fuel Based On Constant Volume Combustion Chamber

Based on the energy structure of "poor oil and rich coal" in China,indirect coal-to-liquid F-T diesel has gradually become a research hotspot of clean alternative fuel because of its excellent physical and chemical properties and its ability to promote clean and efficient utilization of coal.Polymethoxy-dimethyl ether(PODE)and n-butanol,as new renewable oxygen fuel additives,can improve the physical and chemical properties of fuel and promote complete combustion.Blending F-T diesel with PODE and n-butanol theoretically improves the atomization and combustion characteristics of the fuel.In this work,20% of PODE and nbutanol were blended with F-T diesel by volume,respectively,referred to as FFP20 and FBU20.Based on the constant volume combustion chamber,the spray characteristics and combustion characteristics of diesel,F-T diesel,FP20 and FBU20 under different ambient temperature and pressure were compared and analyzed by using high-speed photography combined with MATLAB image processing technology.The study on the effects of ambient conditions on fuel spray characteristics show that compared with 300 K ambient temperature,when the ambient temperature rises to 773 K,the stead-state spray tip penetration of D100,FT100,FP20 and FBU20 decreases by 28.3%,48.5%,50.9% and 53.3% respectively,and the steady-state spray projection area decreases by 72.7%,87.2%,87.5% and 88.5% respectively.The liquid phase spray cone angle decreases significantly after the ambient temperature rises to 673 K.Continued increase in temperature has little effect on the liquid phase spray cone angle.The increase of ambient pressure will increase the air resistance and promote the divergence of oil beam.Compared with the ambient pressure of 3MPa,when the ambient pressure rises to 4MPa,the maximum liquid phase spray tip penetration of D100,FT100,FP20 and FBU2 decreases by 9.3%,8.5%,7.5% and 9.8%respectively.The liquid phase spray cone angle increased by 10.0%,10.5%,5.1% and 5.0%,and the maximum liquid phase spray projection area decreased by 10.2%,12.2%,10.4% and12.9%,respectively.The study on the combustion characteristics of fuel under ambient conditions shows that D100 and FT100 are affected by their own physical and chemical properties.When the ambient temperature and pressure increase,the flame develops more obviously in the axial direction,and the flame front also widens.After adding PODE and n-butanol into F-T diesel fuel,the flame shape is nearly spherical.The increase of ambient temperature will shorten the lightbased ignition delay and the ignition position is closer to the nozzle.Compared with the ambient temperature of 800 K,when the ambient temperature rises to 850 K,the light-based ignition delay of D100,FT100,FP20 and FBU2 was shortened by 30.0%,30.8%,48.0% and 35.6%,respectively.The lift-off length was decreased by 8.3%,20.4%,29.0% and 16.0%,respectively.Compared with the ambient pressure of 3MPa,when the ambient pressure rises to 4MPa,the light-based ignition delay of D100,FT100,FP20 and FBU20 was shortened by 20.9%,15.6%,29.7% and 20.8%,respectively,and the lift-off length was reduced by 10.7%,21.6%,27.1%and 21.8%,respectively.The increase of ambient temperature and pressure will shorten the ignition delay,reduce the lift-off length,and lead to the increase of the diffusion combustion ratio,which will result in the increase of flame area and flame luminosity of the four fuels.The spray characteristics of four fuels were compared at 4MPa and 773 K ambient conditions.The results show that the steady-state liquid phase spray tip penetration,spray projection area and spray cone angle of FT100,FP20 and FBU20 are smaller than those of D100 because of their good atomizing and evaporating performance.Compared with D100,the steady-state liquid phase spray tip penetration and spray projection area of FT100 decreased by26.7% and 51.3%,respectively.Compared with FT100,the steady-state liquid phase spray tip penetration of FP20 and FBU20 decreased by 4.7% and 11.1%,respectively,and the steadystate liquid phase spray projection area decreased by 6.1% and 17.3%,respectively.The difference of steady-state liquid phase spray cone angles between FT100,FP20 and FBU20 is no more than 0.2°.The combustion characteristics of the four fuels were compared at 4MPa and 850 K ambient conditions.The results show that the light-based ignition delay and lift-off length of FT100 decreased by 22.9% and 43.6% compared with D100.Compared with FT100,the lift-off length of FP20 and FBU20 increased by 36.8% and 44.1%,respectively.Due to the high cetane number and high oxygen content of PODE,the light-based ignition delay of FP20 was shortened by 3.7%,and the light-based ignition delay of FBU20 was prolonged by 40.1%due to the effect of high latent heat of vaporization and low cetane number of n-butanol.Compared with D100,the peak flame area of FT100 increases by 8.5%,while the peak flame luminosity decreased by 18.2%.PODE and n-butanol can improve the atomization and evaporation characteristics of fuel,and increase the oxygen content of fuel,and reduce the generation of soot.Compared with FT100,the peak flame area of FP20 and FBU20 decreases by 31.2% and 28.4%,respectively,and the peak flame luminosity decreases by 44.1% and37.9%,respectively.The results of the two-color temperature measurement method show that the addition of PODE and n-butanol to F-T diesel fuel resulted in reduced carbon soot generation and lower combustion temperature of the blended fuel,and FP20 had higher oxygen content and better atomization characteristics,making its carbon soot reduction better than that of FBU20.