Effect Of Methane,Ethane And Propane Doping On Nascent Soot Formation In Ethylene-based Laminar Premixed Flames

Fossil fuel combustion in the engine is the main source of PM2.5 pollution in the city.It is of great significance to study the mechanism of the combustion of soot particles to alleviate the urban air pollution.Actual fuel(such as gasoline,diesel)chemical composition is very complex,direct study of its soot generation mechanism is very difficult.These fuels break down in the combustion process into methane,ethane,propane,ethylene and other small molecules of hydrocarbons,soot particles is to these small molecules of hydrocarbons as a starting point to grow up.Therefore,it is very important to study the formation and evolution characteristics of soot in the flame of small molecule hydrocarbon fuel mixture to understand the mechanism of soot combustion in macromolecule fuel.At present,BSS(Burner Stabilized Stagnation)flame combined with SMPS(Scanning Mobility Particle Sizer)technology has been widely used in the measurement of soot particles due to its reliability.In this paper,the effects of small molecular alkanes(methane,ethane,propane)blending on the formation of primary soot particles(particle size distribution,number density and volume fraction)in a laminar premixed flame were investigated.The chemical reaction kinetics was used to analyze the cause of synergistic effect in flame after alkane blending.It was found that all the blended flames in this paper have bimodal particle size distribution as pure ethylene flame.The blending of small molecular alkanes greatly enhanced the nucleation of soot in the flame,and the strong continuous nucleation was also observed in the downstream of the flame.At the same time,the number density of the soot particles of blended flame is higher than pure ethylene flame because of the presence of soot particles in a large number of nuclear modes.For the blending flame of methane and ethane,when the blending ratio is small,the addition of alkane will promote the growth of soot particles,so the volume fraction of the total soot particles in the flame is larger than pure ethylene flame,that is,the synergistic effect appears.When the blending ratio reaches a certain value,the growth of soot particles is inhibited.The volume fraction of total soot particles in the blended flame is smaller than that of the pure ethylene flame,that is,the synergistic effect disappears.For propylene blends,the synergistic effect is always present.The chemical reaction kinetics analysis,containing the odd carbon of the intermediate substances(such as CH3 and C3H3)on the synergistic effect plays a key role.The synergistic effect of the three alkanes was compared,propane> methane> ethane.