Effects Of Oxygen Concentration And Pressure On Soot Formation In Ethylene Diffusion Flames

Currently,the world's primary energy consumption is still dominated by fossil fuels.Soot is the product of incomplete combustion of fossil fuels.It can pollute the environment and endanger human health.At the same time,it is an important radiation participating medium in flames.Actual combustion equipment generally operates under high pressure.Meanwhile,oxygen concentration affects the combustion efficiency,radiation heat transfer,soot formation and emissions.Therefore,it is of great industrial value to study effects of pressure and oxygen concentration on soot formation and radiation heat transfer in flames.Therefore,in this paper,the ethylene laminar diffusion flame is taken as the research object,and effects of oxygen concentration and pressure on soot formation and radiation heat transfer are studied by numerical simulation.Firstly,numerical simulations are performed on ethylene coflow laminar diffusion flames under different oxygen concentrations.The results show that oxygen concentration affects soot production through the competition between two different mechanisms.On the one hand,the increase of the oxygen concentration causes flame temperature rise and increases the collision nucleation components concentration.These promote the nucleation and surface growth of soot,leading to an increase in the soot concentration.On the other hand,the increase of the oxygen concentration also promotes the oxidation of soot.At the same time,it reduces the height of the flame and the residence time of soot in the flame,resulting in the decrease of the soot concentration.The effect of oxygen concentration on radiation heat loss also comes from two competing mechanisms.On the one hand,the soot concentration and temperature increase with oxygen concentrations,which promote the radiation heat loss.On the other hand,the increase of oxygen concentration leads to the decrease of flame size and the residence time,which reduces the radiation heat loss.Finally,numerical simulations are performed on ethylene coflow laminar diffusion flames under different pressure.The results show that pressure affects the soot concentration through two competing mechanisms.On the one hand,the higher pressure enhances the concentration of collision nucleation components.This will promote the nucleation and surface growth of soot,leading the increase of the soot concentration.On the other hand,the higher pressure also promotes the oxidation reactions of soot,leading to a decrease of the soot concentration.The impact of pressure on the radiation loss also comes from two competing mechanisms.On one hand,the soot concentration increases with pressure,which increases the radiation heat loss.On the other hand,the increase in pressure causes a decrease of the temperature in the flame high-temperature region,which reduces the radiation heat loss.