The Effects Of Synthesis Conditions On The Surface Functional Groups And Oxidation Reactivity Of Soot In The Premixed Methane Flames

Fossil fuel is known to be the main source of energy, which can generate sootparticles that are harmful to the global climate, atmospheric visibility, and humanhealth. In order to protect the environment and human health, the soot particlesgenerated in combustion process must be reduced. Since the achievements on thereaction mechanism of soot formation can provide a theoretical basis for thedevelopment of the soot purification technology, the study on it becomes a researchhotpot in the field of combustion. At present, domestic and overseas scholars haverealized that having a profound understanding on the evolution of the physical andchemical properties have great significances on the research of the formationmechanism of soot particle. The need to provide a better physical and chemicalunderstanding of soot formation in the high-pressure and high-temperature andinhomogeneous engine combustion chamber requires the development of combustionanalysis systems and further fundamental combustion researches. Based on thisbackground, McKenna burner was chosen to produce laminar, atmospheric-pressurepremixed methane flames and soot particles in the flame were sampled using in-situcapillary sampling system (ICCS). Then, the effects of reaction conditions, especiallythe temperature and fuel-air equivalence ratio on the surface functional groups andoxidation reactivity of soot particles were analyzed. The major research work andresults of this dissertation are listed as follows:1、A in-situ capillary sampling system (ISCS) has been developed to samplecombustion products for chemical investigation of soot generated in the premixedlaminar flames produced by the premixed methane/oxygen/argon combustion system.Surface functional groups and oxidation reactivity of soot in burner-stabilized,premixed methane/oxygen flames were studied using Fourier transform infraredspectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA).2、 The relative content of the aliphatic C–H groups on the soot surface, which wasindicated by the normalized peak height ratio (IC-H/IC=C), generally decreases with theincrease of flame temperature. Similarly, the concentration of both C–OH and C=Ogroups also decrease as the temperature increases. The onset temperature（Ti）,maximum rate temperature （Tms）, burnout temperature （Th） and apparent activation energies（Ea）for the oxidation of soot are observed larger in highertemperature flames, indicating oxidation reactivity of soot sampled in highertemperature flame is lower.3、With the increase of fuel-air equivalence ratio, both the The relative content ofthe aliphatic C–H groups and the the concentration of C–OH and C=O groupsdecrease, while the apparent activation energies (Ea) increases from114.28KJ mol-1to148.58KJ mol-1, indicating the soot evolution toward a more graphitic structureand higher resistance toward oxidation as the fuel-air equivalence ratio increases.4、The relative content of surface functional groups has a definite correlation withoxidation reactivity of soot: less surface functional groups would weaken the sootoxidation reactivity.