Study On Synergistic Effect Of Soot Generation From Mixed Hydrocarbon Fuel Diffusion Flame

The pyrolysis-chromatography-mass spectrometry（PY-GC-MS）instrument and the CHEMKIN simulation were used to compare the generation characteristics of the soot formation in the hydrogen-doped hydrocarbon fuel diffusion flames.PY-GC-MS were used to analyze the products derived from the high temperature thermal decomposition of soot.and The C₁-C₉,C₁₀-C₁₃,C₁₄-C₁₅,C₁₆₊products in the soot were quantitatively determined by the relative peak.The flame temperature,soot volume fraction,mole fraction of the main components,and rate of formation（ROP）of each component were obtained through Chemkin simulation.By comparing the results of mixing CH₄,C₂H₆,and C₃H₈ with hydrogen in the ethylene flame,the generation and disappearance of the synergistic effect and the effect of hydrogen mixing on the generation of soot from hydrocarbon fuels are analyzed.The generation paths of soot are analyzed in detail,so as to provide a theoretical basis for reducing the emission of soot particles.The PY-GC-MS analysis shows that the nucleation rate of soot increases when a small proportion of methane is mixed in the ethylene flame,and this phenomenon disappears as the mixing ratio of methane increased.After mixing a small proportion of methane,CH₄ promotes the reaction CH₄+H=CH₃+H₂,etc.which brings a strong chemical promotion effect,leads to a certain synergistic effect,increases the peak value of C₁₆₊,and makes soot nucleation reactions increased.As the mixing ratio of methane increases,the production of OH is promoted,the dilution effect reduces the generation of C₂H₂,and the multi-hydrogen environment covers the surface of polycyclic aromatic hydrocarbons or soot.The increase of the oxidation effect and the reduce of the soot growth caused by the HACA mechanism reduce or eliminate the synergistic effect of soot generation.After mixing hydrogen,the rising rate of CH₃ through CH₄+H=CH₃+H₂ is reduced due to the presence of H₂.The five-membered ring products indene,acenaphthene,fluorene,4H-cyclopentaphene and A₄ increase after CH₄ addition.There is a synergistic effect.After H₂ addition,the synergistic effect generated by these products is reduced or eliminated.The CHEMKIN simulations show that there is a synergistic effect when a small proportion of methane is blended in a methane-ethylene flame,and the synergistic effect disappears with a large proportion of methane blending or H₂ blending.From the simulation results,the reaction CH₄+H=CH₃+H₂ is increased after mixing methane,and CH₃ increases,which promotes the formation of C₃H₃,C₅H₅,C₇H₇,indene,acenaphthene,etc.When the ratio of methane is small,pyrene also increases,inducing a synergistic effect in the generation of soot.The reduction of C₄H₂ and C₂H₂ makes the synergistic effect of A₄ and soot generation disappear at higher CH₄ mixing ratios.After mixing H₂,H₂ inhibits the growth of aromatics and soot caused by HACA mechanism,and strengthens the oxidation of CH₃,C₂H₂,C₃H₃,aromatics,soot,etc.,thereby eliminating the synergistic effect of soot generation.In the ethane/ethylene flames,the synergistic effect is stronger than that in the methane/ethylene flames.There is still an obvious synergistic effect in the ethylene flames blending with 20%C₂H₆,and the synergistic effect is weakened after hydrogen addition.CH₃ is mainly promoted by the reaction C₂H₆+H=CH₃+CH₄.When 30%hydrogen is blended,the mole fraction of each component begins to decrease,and the synergistic reaction in the formation of each component and soot is weaken.In the propane/ethylene flames,the synergistic effect is further stronger.There is still an obvious synergistic effect in the ethylene flames blending with 40%C₃H₈.The synergistic effect is weakened but still obvious after hydrogen addition.CH₃ is promoted by the reaction C₃H₈（+M）=CH₃+C₂H₅（+M）.After hydrogen addition,the mole fraction of each component decreases,and the synergistic effect is weaken.From all the studies,The empirical results shows that the synergistic effect of hydrocarbon fuel has close relations with the fuel structure the formation of soot can be well inhibited by adding hydrogen.