Study On The Formation Of Soot From Diffusion Flame Of Hydrogen-doped Hydrocarbon Fuel

The soot particles produced by incomplete combustion of hydrocarbon fuels are extremely harmful to humans and the environment.The formation of soot causes an increase in heat loss,a decrease in fuel burn-up rate,and at the same time pollutes the atmosphere and affects people's health.Hydrogen is used as a clean fuel,and the combustion product is water.The combustion of hydrogen and other fuels can effectively reduce the generation of pollutants.In this paper,hydrogen was mixed with hydrocarbon fuels such as methane and ethylene in different proportions as theresearch object to studytheeffect of hydrogenonsoot formation.This paper measured the combustion temperature of hydrocarbon fuels,the concentration distribution of soot is measured by LE,and the soot particles at different heights of the flame center were collected by capillary sampling method,and analyzed by Fourier inverse infrared conversion spectrum analyzer,Raman analyzer and Field emission scanning electron microscopy.These equipments were used to study the evolution of functional groups and the degree of graphitization of soot particles along the axial direction of the flame to obtain formation characteristics of soot in methane and ethylene flames under different hydrogen dopingratios.After the methane flame is mixed with hydrogen,the temperature at the center of the flame at different heights increased slightly When the hydrogen doping ratio is 10%,20% and 30%,respectively,which was 27.08 K,25.91 K and 33.66 K higher than the pure methane flame;At the same hydrogen ratio,the hydrogen-doped ethylene flame increased by 28.98 K,19.12 K and4.14 K.The temperature increase of ethylene flame after blending was not as obvious as methane.And when the hydrogen doping ratio was 10%,20% and 30%,the peak concentration of ethylene flame soot was 6.38 ppm.Under the same proportion of hydrogen,the peak concentration decreased to 6.21 ppm,6.14 ppm and 5.99 ppm respectively.The integrated value of the cross-sectional area of the concentration decreased with the increase of hydrogen doping ratio.Both methane and ethylene flame products contained an aromatic functional group,aliphatic functional groups,and carbonyl functional groups no matter the hydrogen is doped or not.The relative content of aliphatic functional groups at the center of the flame firstly increased and then decreased along the height of the flame,indicating that in the direction of the flame height,the transition from surface growth to high temperature oxidation was dominant.After blending with hydrogen,the relative content of methane and ethylene flame carbonyl functional groups increased significantly at the same flame height position compared with the unblended content,but the increase extent was different.After blending with hydrogen,the content of aromatic functional groups in methane flame increased significantly compared with unblended one.The relative content of aromatic functional groups in ethylene flame was significantly lower than that in unblended,indicating that hydrogen had different effects on the combustion oftwo fuels.In the methane and ethylene flames,the AD1/AG values which indicates the degree of graphitization of the particles first decreased and then increased along the height direction,indicating that the particles experienced a process of increasing the degree of graphitization and then increasing,but the difference of two flames AD1/AG is significant,meaning that the degreeof graphitization of thesoot producedby thetwo flames was different.With the increase of height,the structure of the soot appeared spherical,multi-spherical clusters,cluster,and fiber-like structures in the height direction.This evolution corresponded to the nucleation,collision condensation and oxidation process of soot particles..When the hydrogen doping ratio of methane is 10% and 20%,the agglomeration of the soot particles in the low flame zone was earlier compaired with unblended one.However,when the hydrogen doping ratio is 30%,the phenomenon of agglomeration advanced was not obvious;The morphology of the downstream region of the flame was more denser and more mature after mixing with hydrogen,and this phenomenon was more obvious with the increase of hydrogen..The phenomenon of agglomeration advancement was not observed in the low flame zone of ethylene flame,and the particle morphology in the downstream region of the flame changed slightly.