Experimental Study On The Effect Of Hydrogen Doping On The Formation Of Soot In Methane/Ethylene Diffusion Flame

The soot produced by incomplete combustion of hydrocarbon fuels is harmful to human health and the natural environment,causing various diseases and serious air pollution problems.The knowledge of generative characteristics is not yet sufficient.Based on the ethylene flame,this paper explores issues such as the effect of hydrogen on the soot formation of ethylene,the synergistic effect of methane and ethylene,and the soot characteristics of hydrogen/ethylene flame after adding different proportions of methane.It aims to analyze the suppression effect of hydrogen as a clean fuel on the soot formation from hydrocarbon fuels and the similarities and differences in the formation mechanism of soot from different types of hydrocarbon fuels.In order to solve those problems,the author builted a laminar diffusion flame combustion system to measure the soot concentration by the extinction method,and soot particles were collected by capillary tube.Various aspects of characteristics such as the soot concentration in the flame,the surface functional groups,the degree of graphitization and morphology of particles have been studied,the specific results are as follows:1.Pure ethylene flame soot is mainly distributed in the areas on both sides of the flame.It first increases and then decreases in the height direction.When the blending ratio is 3%,ethylene and methane have a synergistic effect,but this phenomenon does not appear in the other proportions.Hydrogen can inhibit the formation of soot in ethylene,and the inhibition will increase with the increase of hydrogen addition.When the three gases are mixed together,the synergistic effect between ethylene and methane will disappear,indicating that the inhibition effect of hydrogen on soot formation is greater than the promotion effect of methane on soot formation at this ratio.2.In pure ethylene flame,different forms of aromatic functional groups change differently.And the contents of aliphatic functional groups and carbonyl functional groups first increase and then decrease.After addition of methane,the changes of aromatic functional groups are more consistent.The addition of a small proportion of methane further promotes the growth of soot,resulting in a significant increase in aliphatic content,and the increase in carbonyl functional groups is most obvious when the blending ratio is 3%.The addition of hydrogen reduces the aromatic functional groups,which is most significant at 30% blending ratio.Hydrogen reduces the oxidation activity at low flame heights,while it promotes the oxidation of particles at higher heights.After ethylene and hydrogen are mixed together,adding methane(3%and 5%)in a small proportion makes the content of meta-disubstituted C-H aromatic functional groups increase significantly relative to the rest of the aromatic functional groups.3.As the flame height increases,soot particles of the pure ethylene appear in droplets,loose clusters and tight network structures in sequence.As the amount of hydrogen blended increases,the soot particle size gradually becomes larger,and the distribution and compactness of aggregates are also different at 2cm.After pure ethylene was mixed with 3% methane,the droplet-like structure at 2cm was reduced,and the cluster-like structure appeared in advance.After addition of 30% methane,the droplet-like structure and the cluster-like structure disappeared.In a pure ethylene flame,as the flame height increases,the degree of graphitization gradually increases,and the degree of disorder gradually decreases.After mixing with methane,the degree of graphitization increases compared with that of pure ethylene.After the proportion increases,graphitization degree has dropped again.The effect of hydrogen addition on the degree of graphitization in the low flame and high flame areas is opposite.When the three are mixed together,the degree of graphitization is different from that of adding them separately.