Effect Of DMC/Diesel Blending Fuels On Physicochemical Characteristics Of Diesel Engine Exhaust Soot

The soot particles emitted by diesel engines is harmful to the atmosphere and human health.Fortunately,the application of alternative oxyfuels can effectively reduce the emission of soot.As known,the changing of fuel composition has a great influence on the soot physicochemical properties,thus affecting soot oxidation reactivity.This study investigated the physicochemical properties of soot generated from diesel engine fueled with D100(neat diesel),DMC8.3(91.7 vol%D100+8.3 vol%DMC),DMC15 and DMC25.The main analytical instruments include Transmission electron microscopy(TEM),Raman spectroscopy(Raman),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and thermogravimetric analyzer(TGA).The results showed that DMC/diesel blends can effectively reduce soot emission with respect to D100.For the soot physical properties,fractal dimension(D_f)and primary particle diameter(d_p)decreased with the increment of DMC blending as well as the nanostructure of primary particles became more disordered(shorter La,wider d and greater T_f).However,Raman analysis showed that the addition of DMC would increase the graphitization degree of soot.Under the same engine speed condition,the D_f of D100soot and DMC/diesel blends soot decreased and the order degree of nanostructure of primary particles increased with the elevation of engine load.When the engine load increases,the d_p exhibit an increasing trend at 1400rpm,while decreased at 2200rpm.Independently of engine load,with the increase of engine speed,the D_f of all the soot samples decreased as well as the d_p increased and the nanostructure became more ordered.On side of soot chemical properties,the addition of DMC in diesel would increase the aromatic C-H functionalities content,decrease the aliphatic C-H functionalities content,increase the oxygenated functionalities content and carbon hybridization ratio(sp~3/sp~2).Under the same engine speed,the increment of engine load would cause the aromatic C-H functionalities content,aliphatic C-H functionalities content and sp~3/sp~2 ratio of soot particles to decrease,while the content of oxygenated functionalities would increase.Under the same engine load conditions,with the increase of engine speed,the aromatic C-H functionalities content increases,while the aliphatic C-H functionalities content and oxygenated functionalities content as well as the carbon sp~3/sp~2 ratio decreases.As the increment of DMC blending,the oxidation reactivity of soot was gradually enhanced.At lower engine speed,the oxidation reactivity of D100 soot was enhanced with the increase of engine load,while the oxidation reactivity of DMC/diesel soot was weakened.However,the oxidation reactivity of D100 and DMC/diesel soot both decreased with the increase of engine load at higher engine speed.Under the same engine load,the oxidation reactivity of soot would be improved with the increase of engine speed.Sensitivity analysis showed that the aromatic C-H functionalities content,D_f,sp~3/sp~2 and primary particle nanostructure were the main factors determining the soot oxidation reactivity,while the d_p,aliphatic C-H functionalities content,O/C ratio and the oxygenated functionalities content were the secondary factors governing the soot oxidation reactivity.