Study On Laminar Combustion Characteristics Of Lean Combustion Of Syngas Under Preheating Condition

Energy and environmental issues have been widely concerned by all countries in the world,which is the lifeblood of national economic development and the key to the survival of human beings.Typical syngas is mainly composed of H₂,CO,CH₄,CO₂,N₂and a small amount of other high hydrocarbon gases.In the process of production and application,it shows the shortcoming of low calorific value,poor combustion speed and low thermal efficiency,which undoubtedly restricts the development of syngas in industrial production and application.Therefore,an in-depth understanding of the combustion characteristics of syngas（such as laminar burning velocity,flame instability and flammability limit）is of great significance to the efficient utilization of fuel and the safe operation of equipment.Firstly,the laminar burning velocity of the synthesis gas/air mixture with different fuel components was measured under the conditions of equivalent ratio keeps 0.4-1.0and initial temperature is 300K-500K using the self-built capacity incendiary bomb experimental platform,and the flame tensile instability has been analyzed.Experimental results show that the laminar burning velocity of the syngas increases with the increase of the equivalent ratio,the initial temperature and the H₂content in the fuel.With the increase of the H₂content,the increase of laminar burning velocity caused by the initial temperature also increases,but the higher the H₂content,the less sensitive the laminar combustion rate to the initial temperature.In addition,the Maxtain length of the fuel shows a decreasing trend with the equivalent ratio,the initial temperature and the increase of the H₂content in the fuel.When the value of Maxtain length is greater than1,the flame tends to be tensile stable.Secondly,the chemical kinetics analysis of laminar combustion process of syngas/air mixture under the same operating conditions was carried out by CHEMKIN numerical simulation software and GRI-3.0 mechanism.The effects of equivalence ratio,fuel composition and initial temperature on flame structure were analyzed in terms of adiabatic flame temperature,fuel composition,important free radicals,combustion rate sensitivity and reaction path,etc.The simulation results show that with the progress of combustion reaction,the content of CO in the unburned gas increases with the increase of equivalent ratio,initial temperature and the H₂content in the fuel.The adiabatic flame temperature of fuel and the concentration of important free radicals H,OH and O also showed the same variation law.The sensitivity analysis and reaction path analysis showed that with the increase of H₂content and the initial temperature,and the optimization of CH₄oxidation path is the main reason for the acceleration of combustion process.Finally,in order to analyze the influence of initial temperature and fuel components on the inherent instability of the flame,the parameters such as the temperature field change and thermal diffusion coefficient that are not easy to measure in the experiment are obtained by numerical simulation.The effective Lewis number and flame thickness of the fuel under different initial conditions are indirectly obtained.The thermal diffusion instability and hydrodynamic instability of the flame are analyzed.The results show that with the increase of the equivalent ratio,H₂content and initial temperature,the heat diffusion of the flame instability and hydrodynamic instability show an enhancing trend.However,with the increase of H₂content,the initial temperature is unstable to the thermal diffusion of the flame.The enhancing effect of hydrodynamic instability is weakened.The study of laminar combustion characteristics of syngas under different initial conditions has important theoretical significance and engineering application value for the stable combustion of flame,the improvement of combustion efficiency and the reduction of pollutant emission.