Studies On Surface Functional Groups And Oxidation Reactivity Of Soot In A Ethylene/Air Premixed Flame

The study on soot formation mechanism can provide theoretical basis and technicalsupport for reducing particulate emissions and it presently becomes research focus. In order tostudy the evolution of soot in the premixed flame and improve the soot formation mechanism,a ethylene/air premixed flame combustion system was established in this paper. Soot wascollected from flame at different maximum flame temperature and fuel air equivalent ratioabove the burner (HAB) by using in-situ capillary sampling system (ICCS). Besides, surfacefunctional groups and oxidation reactivity of soot in the flame were studied systematicallyusing FT-IR, XPS and TGA. The major work and achievements of the paper are listed asfollows:(1) At the same fuel-air equivalent ratio, with the increase of flame temperature, therelative content of the aliphatic C–H surface functional groups (AC-H/AC=C) of soot rangeswithin0.32~3.54. The content of oxygenated C-OH and C=O surface functional groups are inranges of8.61~11.68%and4.89~11.44%,respectively. The onset temperature(Ti), maximumrate temperature (Tms), burnout temperature (Th)of soot all show a growth trend, and apparentactivation energies(Ea) changes in the range of140.67~182.71KJ/mol, indicating that sootparticles are more graphitization degree and oxidation reactivity of soot particles in the lowerflame height are lower with the increase of flame temperature.(2) At the same flame temperature, with the increase of fuel-air equivalent ratio, therelative content of aliphatic C–H surface functional groups (AC-H/AC=C) ranges from0.21to3.18. The content of oxygenated C-OH and C=O surface functional groups are in the range of10.38~15.65%and6.27~13.93%, respectively. The onset temperature(Ti), maximum ratetemperature (Tms), burnout temperature(Th) of soot are in the range of492.25~530.75℃,586.75~655.42℃and643.58~724.17℃,respectively. The apparent activation energies(Ea)firstly increases and then decreases, revealing that the oxidation reactivity of soot varies froma decrease to an increase.(3) The surface functional groups of soot have direct correlation with its oxidationactivity, that is, less surface functional groups could lead to larger apparent activation energiesand lower oxidation activity at the height of25mm.