Numerical Simulation Of Combustion Strength And Stretch Characteristics Of Fully Premixed Flame With Steady Flame

With the continuous progress of the "carbon peaking and carbon neutrality" goals,natural gas as an important carbon source,how to use efficient and low pollution has become the key to achieve energy transformation.Natural gas industry is developing rapidly.In addition to civil cooking,natural gas is also widely used in petrochemical industry,machinery manufacturing,metal smelting and other industrial fields.The fully premixed flame with stable flame not only has low pollutant emission and high flame heat release rate,it has great advantages in the industrial field.In this thesis,full premixed flame is taken as the research object,and the combustion strength and stretch characteristics of full premixed flame and full premixed flame under steady flame are studied by numerical simulation.Two dimensional numerical models of fully premixed flame and fully premixed flame with stable flame were established.The laminar finite rate chemical reaction model was selected and the methane-air multi-step reaction mechanism with 16 components and 41 reactions was adopted.The simulation model was verified by experiments.The flame height H,root lifting distance h,integral consumption speed Sc,modified integral consumption speed Sc’ flame stretching rate κ and their distribution terms were obtained by simulation.The effects of flame equivalent ratio airflow velocity Vi,stable flame equivalent ratio φ2 and airflow velocity V2 on flame characteristics were analyzed.Get the best steady flame condition.The simulation results show that fully premixed flame Sc decreases gradually from the top of the flame to the root of the flame.When Vi=1 m/s,φ1=0.90,Sc decreases from 0.271 m/s to 0.125 m/s.On the one hand,H2O and CO2 are diffused into the flame preheating zone,and the differences in diffusion velocity and direction between components lead to higher concentrations of H2O and CO2 in the flame root preheating zone than in the flame top preheating zone,diluting CH4 and O2 in the root preheating zone and weakening Sc.On the other hand,the thermal conductivity of the reaction zone in the flame root to the preheating zone decreases,leading to a gradual decrease of Sc.When Vi is constant and φ1 increases,H,h decreases and Sc at the flame root increases.When φ1 is constant and Vi increases,H,h increases and Sc at the flame root decreases.The κ at the top of the flame was the largest and the curvature κc was the main,and the strain rate κs was negligible.At the root of the flame,κc and κs were both decreased and the decrease amplitude was basically the same when V1 was unchanged and φ1 was increased.When φ1 was constant and V1 increased,both κc and κs increased but κs increased more than κc.There is a full premix flame with stable flame.The stable flame leads to higher H2O and CO2 concentration on the main side(No stable flame side)of the preheating zone at the same level height than that on the stable side(There is a steady flame side),which weakens Scc’-m.At the same time,the main heat-conducting side of the reaction zone towards the preheating zone is lower than that on the stable side,which leads to the steady side modified integral consumption speed Scc’-s greater than Sc’-m.When V2 is constant and φ2 increased,H first increased and then decreased,and the turning point was φ2=1.20.Stable side root lift distance hs decreased,Sc’-s increased at the flame root,and Sc’-s was greater than Sc’-m.When φ2 is constant and V2 is increased,H decreases,hs decreases,Sc’-s at the flame root increases,and Sc’-s is greater than Sc’-m in all cases.V2=0.5 m/s,φ2 increased from 1.10 to 1.30,Sc’-s increased from 0.106 m/s to 0.144 m/s,φ2 increased significantly after 1.30.φ2=1.20,V2 increased from 0.5 m/s to 0.7 m/s,Sc’s increased from 0.130 m/s to 0.155 m/s,and the increase of Sc’-s of V2 decreased significantly after 0.7 m/s.flame root κc and κs are steady side is greater than the primary side,but κc difference is greater,φ2 or V2 changes,κc and κs are steady side change degree is greater than the primary side.The steady flame improves the burning intensity of the full premixed flame root,based on the simulation of fire hole size,spacing and condition parameters,the best working condition of the stability of flame is φ2=1.30,V2=0.7 m/s.