Study On The PAHs Formation Characteristics In Laminar Premixed Small Molecular Alkanes And Olefins Flames

The polycyclic aromatic hydrocarbons?PAHs?generated from the incomplete combustion process of fossil fuels are kind of carcinogenic,teratogenic and mutagenicity substances.And PAHs are considered to be the important precursors of soot.To study the formation characteristics and generation mechanism of PAHs in the combustion process has become a research focus in the combustion field.In this paper,laser induced fluorescence?LIF?technology with no interference to the flame and high space-time resolution was applied to measure the PAHs fluorescence intensity in laminar premixed stagnant flames of small molecular alkanes and olefins.Meanwhile,the Chemkin software and KAUST2 soot formation mechanism were combined to simulate the experiment conditions,and then analyzed the influence of combustion conditions and fuel structures on the PAHs formation in laminar premixed flames.The main works and results are as follows.?1?PAHs evolution in flame with height above burner:The PAHs fluorescence intensity increased with the increase of height above burner in laminar premixed C₂H₆ flames.The fluorescence spectrum shape was basically the same at different heights above burner and centered on the fluorescence wavelength of 500nm.?2?The influence of combustion conditions on PAHs formation:In the condition of same flame temperature and residence time,the PAHs fluorescence intensity increased with the addition of equivalent ratio in laminar premixed C₂H₆ flames.The simulated results showed that the molar concentration of C₂H₂ and C₃H₃ increased with the equivalent ratio,then promoted the formation of benzene and PAHs.In the condition of same equivalent ratio and residence time,the PAHs fluorescence intensity appeared increased firstly and then decreased with the rise of flame temperature.The main reason was that the PAHs formation activity higher than consumption activity in low temperature condition,while in the high temperature condition was just the opposite.The temperature mainly influenced the reaction rate of PAHs formation and consumption and the molar concentration of benzene,then lead to the difference of PAHs concentration.?3?The influence of fuel struture on PAHs formation:In the condition of same combustion condition and residence time,the PAHs fluorescence intensity in C₃H₈ flame was higher than in C₂H₆ flame,and in C₂H₄ flame was also higher than in C₂H₆ flame.The simulated results showed that the molar concentration of C₂H₂ and C₃H₃ in C₃H₈ and C₂H₄flame were higher than that in C₂H₆ flame.The PAHs fluorescence intensity in n-C₄H₈ was higher than that in i-C₄H₈ flame,which meaned that normal alkene was favorable to PAHs formation than branched alkene.