Study On Characteristics Of Generation And Transformation Of Soot Formed From Methyl Octanoate Blended With N-butanol

With the energy crisis intensifying and environment problem becoming increasingly prominent,biodiesel and biofuels,as the promising renewable energy,have been getting more and more attention.Because the composition of biodiesel is very complex,we usually use biodiesel surrogates or surrogate mixtures instead of biodiesel for the primary experiment,mechanism and chemical kinetic research.Soot particles are one kind of major pollutant from fuel incomplete combustion.Soot emission to the environment reduces air quality,affects the climate and can cause health problems.The formation mechanism and the evolution process of soot particles have become the research focuses.Therefore,it is of great importance to understand the characteristics including nanostructure and reactivity of soot at different operating conditions,which can help to reduce soot emission.In this paper,methyl octanoate is chosen as the biodiesel alternative and n-butanol as the biodiesel additive,investigating the characteristics of generation and transformation of soot from methyl octanoate blended with n-butanol at different operating conditions.Firstly,by detailed chemical kinetic analysis on pyrolysis of methyl octanoate blended with different proportions of n-butanol,the influence of n-butanol addition on the pyrolysis characteristics of methyl octanoate has been studied.It was discussed that the effects of n-butanol addition on the main products and intermediate products,especially the soot precursor.And the chemical effects of n-butanol have been identified.The results show that,the higher n-butanol addition is,the lower the peak concentrations value of products in the pyrolysis process.At the higher temperature,n-butanol chemical effects can increase mole fraction of the major species and intermediate species,but n-butanol dilution/thermal effects decrease the mole fraction of soot precursor such as C2H2,C3H3,C4H2,C4H4.And n-butanol dilution/thermal effects are stronger as the n-butanol addition increases.Secondly,the characteristics of generation soot from co-pyrolysis of biodiesel surrogate methyl octanoate blended with n-butanol,performed in a quartz tube flow reactor operating at different pyrolysis temperature and mole fraction of n-butanol,are studied systematically using transmission electron spectroscopy(TEM),X-ray diffraction(XRD)and thermogravimetric analyzer(TGA).Results show that,soot amount decreases as the n-butanol addition rises,but the soot amount increases with the rise of pyrolysis temperature.Increasing the temperature and n-butanol addition,the changes in soot nanostructure and reactivity show the same trends:smaller particles,larger fringe length,lower tortuosity,lower separation and oxidation reactivity.That is to say,as the two parameters rise,the soot graphitization degree increases and structural disorder decreases.Finally,the transformation characteristics of the nascent soot from methyl octanoate combustion blended with n-butanol in inverse diffusion flame(IDF)have been investigated by the photoflash exposure.Additionally,the role of n-butanol addition on the nascent soot generation characteristics has also been studied.The finding suggest that,compared to soot from methyl-octanoate-doped ethylene IDF,n-butanol addition leads to smaller nascent soot particle size,larger fringe length,lower tortuosity,lower separation and oxidation reactivity.Besides,the photoflash exposure can reduce the amount of nascent soot generated from different flames.By flashing 20 times in air,soot nanostructure can be reconstructed substantially without burning and the changes in properties of different nascent soot have shown the same tendency:smaller particles,larger fringe length,lower tortuosity,lower separation and oxidation reactivity.It indicates that the degree of soot crystallization increases while the soot reactive rate decreases after flash.Moreover,the effect of 1 flash time on nascent soot is not obviously,and the changes in nanostructure and oxidative reactivity of soot in Ar are higher than that in air due to their different thermal conductivities.