Research On Combustion And Emission Characteristics Of Micro-emulsified F-T Diesel

F-T diesel is a clean alternative fuel refined by coal indirect liquefaction technology with low sulfur and aromatic content.However,the F-T diesel has a high cetane number and a low kinematic viscosity,which causes diesel engine emissions to deteriorate under some conditions.In order to improve the partial physicochemical properties and emission performance of F-T diesel,micro-emulsified F-T diesel was prepared by micro-emulsification technology.The effects of water and surfactant content on the physical and chemical properties,combustion emission characteristics and economy of micro-emulsified F-T diesel were studied.The surface oxygen-containing functional groups and oxidation characteristics of particulate matter emitted by micro-emulsified F-T diesel fuel were analyzed.Three kinds of micro-emulsified F-T diesel fuels with M3,M4 and M5.5(Water content is3%,4%and 5.5%respectively)were prepared based on surfactant screening method and micro-emulsification principle,and their main physical and chemical properties were measured by experimental equipment.The results showed that,compared with pure F-T diesel,the viscosity,freezing point and oxygen content of micro-emulsified F-T diesel increased with the increase of water and surfactant content.Micro-emulsified F-T diesel droplet size is mainly distributed in the region of 10~100 nm.with the increase of water content,the particle size distribution range narrowed,and the average particle size of droplet particles reduced.Based on thermogravimetric analysis experiments,the thermal analysis kinetics of experimental fuels was carried out.It was found that,the activation energy of micro-emulsified F-T diesel was higher than F-T diesel,and the ignition property was worse.The fuel economy of microemulsified F-T diesel was calculated and analyzed.The results showed that,at the same speed,the effective fuel consumption rate of micro-emulsified F-T diesel and pure F-T diesel was basically the same at full load,and slightly higher under other loads.The effects of water and surfactant content on the combustion characteristics and emission characteristics of microemulsified F-T diesel were studied by bench experiments.The results showed that,at full load and rated speed of 3600 r/min,with the increase of water and surfactant content,the retardation period of M3,M4 and M5.5 was prolonged,and the maximum combustion pressure and instantaneous heat release rate in the cylinder were obtained.The peak was higher than pure F-T diesel;At the maximum torque point speed of2700 r/min,compared with pure F-T diesel,the peak in-cylinder combustion pressure and instantaneous heat release rate of M5.5 were significantly reduced,and M3 and M4 were not much different.At the same speed and full load,the NO_X,CO and soot emissions of micro-emulsified F-T diesel were 20%lower than pure F-T diesel,and the decrease under other loads was smaller.At low loads,M3,M4 and M5.5 had slightly higher HC emissions than pure F-T diesel;However,at medium and high loads,micro-emulsified F-T diesel HC emissions were slightly lower than pure F-T diesel.Based on the thermogravimetric analyzer(TGA)and X-ray photoelectron spectroscopy(XPS),the effects of water and surfactant content on the surface oxygen-containing functional groups,carbon atom hybridization mode,O/C and oxidation activity of the particulate matter of micro-emulsified F-T diesel were analyzed.The results showed that,compared with pure F-T diesel,the relative oxygen content of hydroxyl groups(C-OH)and carbonyl(C=O)on the surface of the particulate matter of M3,M4 and M5.5 increased with the increase of water and surfactant content.The sp~3/sp~2 of C atom also rose,and the degree of surface disorder of the particles increased.The particulate matter of M3,M4 and M5.5 had a lower oxidation temperature range,and their oxidation activity was enhanced.