Study On The Characteristics Of Soot/PAH Formation In Prenol And Iso-prenol Counterflow Diffusion Flames

Soot is one of the main pollutants emitted by engines,which will cause many adverse effects on the atmospheric environment and human health.With the increasing pressure of carbon emission reduction,biofuels represented by alcohol fuels have received more and more attention due to their clean,renewable,and carbon neutral advantages.Researchers have discovered that 3-methyl-2-buten-1-ol（referred to as prenol）has the potential to be used as a new generation of alcohol fuel or gasoline and diesel additives.When it is blended with gasoline,the octane number of the mixed fuel is significantly increased,which means that the compression ratio of the gasoline engine can be increased,thereby increasing the thermal efficiency.However,there is currently no relevant research on the characteristics of soot formation in prenol combustion.Therefore,in this paper,a laser measurement system based on the counterflow diffusion flame is built to measure the volume fraction of soot in the flame and the relative concentration of polycyclic aromatic hydrocarbons（PAH）;a mechanism containing containing 957 species and 4833 step elementary reactions is coupled.It is used to calculate the PAH formation of prenol flame.The specific research content and conclusions are as follows:First,the influence of different nozzle exit velocities and oxygen mole fractions on the formation of soot form the counterflow diffusion flame is studied,and the basic understanding of the formation of soot from the counterflow diffusion flame is obtained,which is the basis for subsequent research.Secondly,3-methyl-3-buten-1-ol,isopentane,isopentene,and isopentanol,were selected for comparison with 3-methyl-2-buten-1-ol to Explored the influence of molecular structure on soot formation.The sooting tendency of the five fuels is:isopentane>3-methyl-2-buten-1-ol>3-methyl-3-buten-1-ol>isopentane>isopentanol.From the perspective of molecular structure,fuels containing hydroxyl have a lower sooting tendency than the corresponding fuels without hydroxyl,and fuels containing carbon-carbon double bond have higher sooting tendency than the corresponding fuels without carbon-carbon double bonds.The closer the carbon-carbon double bond is to the end of the molecular structure,the lower the sooting tendency is.The analysis of the reaction path explains the reason for the difference in the sooting tendency of different fuels.After that,methane and ethylene were selected as basic fuels,and two different gaseous atmospheres were provided to explore the soot formation characteristics of prenol blended fuels.The results showed that both prenols promoted the production of methane and ethylene PAH/soot,and their effect was related to the molecular structure of prenol and the nature of the basic fuel itself.Different molecular structures led to a wide difference in the path and tendency of PAH/soot formation.3-Methyl-2-buten-1-ol may have a closer chemical crosslink with the C₂ species in the nucleation reaction.Finally,n-heptane and iso-octane were selected as gasoline reference fuels,and the effect of prenol blending on soot formation is studied.The results show that as the proportion of prenol blended in n-heptane increases,the PAH/soot formation of the mixed fuel is monotonously enhanced.As the proportion of 3-methyl-3-buten-1-ol blended in iso-octane increases,the PAH/soot generation of the mixed fuel decreases monotonously.As the proportion of 3-methyl-2-buten-1-ol blended with iso-octane increased,the PAH-LIF signal of the mixed fuel increased slightly,and the soot volume fraction showed a significant increase.The reaction path analysis shows that the pyrolysis of n-heptane mainly produces a large amount of ethylene and a small amount of propene;the pyrolysis of iso-octane mainly produces iso-butene and propene,and the formation of A1 in the iso-octane flame is mainly through the odd-number channel related to the C₃species,and the 3-methyl-2-buten-1-ol flame has a higher concentration of acetylene,and can generate a large amount of 1,3-butadiene radicals to accelerate the C₂+C₄ path generates A1,so by promoting the growth of PAH and the surface growth of soot,the soot formation of the blended fuel is significantly enhanced.