Effects Of Different Oxygenated Fuels On Soot Formation In N-heptane/iso-octane Atomized Combustion Flames

With the worldwide implementation of Carbon neutral and increasingly stringent emission regulations,there is an urgent need for renewable and clean traditional energy alternatives,in which biomass energy is a fuel with great potential for future applications.Because its physical and chemical properties similar to those of traditional energy sources.It uses natural plants as raw materials for its production and own oxygen-rich properties,and its production and preparation technologies is mature.Like traditional hydrocarbon fuels,they produce greenhouse gas,CO₂ and air pollutants such as soot and NO_x?CO.Therefore,it is very important to study the combustion and soot formation mechanism of oxygenated biomass fuel for its future application.The effect of ethanol(E15),Butanol(B15),hexanol(H15),furan(F15)and 2,5-dimethyl furan(DMF15)oxygenated fuels mixed with 15%volume fraction on soot formation in the atomization combustion flame of N-heptane and iso-octane was investigated.The variation of the characteristic parameters such as morphology,particle size,nanostructure,deposition morphology,material composition,type,content and oxidation activity of soot in different stages were analyzed.Based on copper mesh thermophoresis probe,SiC fiber deposition and capillary dilution sampling,and transmission electron microscopy(TEM),field emission scanning electron microscopy(FSEM),Raman spectroscopy,Fourier transform infrared spectroscopy and thermogravimetric analysis.The following conclusion were obtained:(1)Under the experimental conditions of this paper,The size of soot particles increases first and then decreases.Oxygen-containing fuels can inhibit the growth of soot particles first and then promote the growth of soot particles,and can reduce the particle size of soot particles in oxidation stage.The intensity of this effect is proportional to the alcohol carbon chain,and the effect of furan fuel is more obvious.(2)As the sampling position increases,the crystal size of soot particles increases first and then decreases,the curvature decreases first and then increases,and the interlayer spacing increases first and then decreases.With the increase of the alcohol carbon chain and furan methyl,the curvature of the mature soot particles decreased with the increase of the carbon chain and furan methyl.The degree of graphitization of soot particles increases monotonously with the increase of sampling position.Alcohols decrease the degree of order of primary and aged soot and increase the degree of order of mature soot.Furan reduced the order degree of primary and mature soot and increased the order degree of aged soot.In general,the disordered carbon and polycarbon at the edge of the crystal will decrease with the increase of the sampling height,but the carbon added with ethanol and furan will decrease monotonously and the content will be very small,these two kinds of carbon structure increase with the increase of alcohol carbon chain and Furyl branch chain.(3)The most abundant soot is aliphatic functional groups and carbon-oxygen functional groups,followed by olefins and aromatic substances.With the increase of sampling height,the content of most functional groups in the samples generally increases first and then decreases.Carbon-oxygen functional groups decreased sharply while aliphatic radical decreased relatively slowly.aromatic groups contain more asymmetric aromatic branched chains C-H functional groups.The content of CH₂in aliphatic functional groups is much more than CH₃,and the functional groups are mostly stable symmetric saturated functional groups.The addition of oxygen-containing fuels reduces aromatic substances and symmetric saturated functional groups,which weakens with the increase of alcohol-carbon chains.Furan fuel did not increase the aromatic content,but the existence of methyl branched chain reduced it.The content of symmetric C-O functional groups of aromatic and vinyl groups is much higher than that C-O asymmetric functional groups.The addition of oxygen-containing fuels increases the content of oxygen-containing functional groups,which is proportional to the methyl branched chain of furan and inversely proportional to the alcohol-carbon chain.The content of olefins is more than that of aromatics,the increase of alcohol-carbon chain reduces the increase of olefins,the olefins in the middle of furan fuel flame are more than aromatics,while in the higher position of flame,aromatics are more than olefins.(4)With the increase of sampling height,the oxidation temperature of each characteristic of soot increases.Compared with the base fuel,the oxidation temperature of soot added with furan fuel has little change,and the oxidation temperature of soot E15 increases,which may be caused by the high aging degree of soot samples.With the increase of alcohol carbon chain length,the oxidation temperature decreases,and the apparent activation energy of soot below the midpoint of flame is reduced by adding oxygen-containing fuel.The increase of alcohol fuel carbon chain and furan fuel branched chain increases the apparent activation energy of aging soot.E15 the average apparent activation energy of soot is the lowest,it is the easiest to be oxidized,but its maximum weight loss rate and the corresponding temperature of burnout are very high,indicating that the oxygen content of fuel can reduce the initial reaction temperature of soot.But it is easy to form some refractory crystals.(5)Compared with N-I0,the addition of oxygen-containing fuel makes the sediment in low position dispersed,and the single particles are obviously and uniformly distributed.However,with the increase of alcohol carbon number,the sediment distribution becomes chaotic and the particle size varies greatly.The furan fuel reduces the size of soot deposited particles and the DMF15 ratio is F15 obvious.With the increase of sampling height,the influence of flame temperature on sediment is dominant,and the morphology of sediment is directly related to temperature.(6)special structure,the higher the difference of oxidation activity,the easier it is to form special structure.Due to the difference of functional group content and graphitization degree of soot,there is a great difference of oxidation activity in the same soot sediments.Under the condition of high temperature,the high active soot is easy to oxidize,and the dense special sediment structure is formed by the secondary combustion consumption agglomeration of the general sediment around.