Study On Transition Characteristics Of Soot Produced From Aviation Alternative Fuel Ndecane Flames

With the continuous advancement of technology,the aviation industry has developed rapidly,and the main pollutants such as soot particles generated during the combustion of aviation fuel impact environment and human society.Therefore,it is of great significance to understand the soot generation characteristics of aviation fuel and propose a method for controlling soot generation to reduce the emissions of combustion pollutants.Because the composition of aviation kerosene RP-3 is very complicated,it is difficult to carry out experiments and build chemical kinetic models.Therefore,in practice,simple kerosene surrogates with similar physical and chemical properties are generally used for research.In this paper n-decane was selected as an alternative fuel for RP-3 to identify transition point of soot generation from n-decane counterflow diffusion flame,further to study the combustion chemistry of n-decane flame soot formation process.The influence of the combustion atmosphere on the soot formation was also explored.Firstly,n-decane combustion experiment was performed on counterflow diffusion experimental system to find transition point of soot generation,RGB parameter values of flame image were extracted by MATLAB,and transition point of soot generation was obtained by analyzing RGB image combined with flame image.The results showed that increasing oxygen concentration,reducing nitrogen flow rate,and increasing fuel flow rate could gradually produce soot particles in the flame.By controlling the single change of the three groups of parameters,it was identified that transition point of soot generation was oxygen concentration of 38%,diluted N₂ flow rate of 420ml/min,and fuel flow rate of 0.320ml/min,respectively.Further exploring transition point changed in different combustion atmospheres,and replacing oxidant side and fuel side N₂ with CO₂,it was found that transition point of soot generation on oxidant side and fuel side were oxygen concentration of 44%and 42%,compared with the results of N₂ atmosphere,transition point shifted to higher oxygen concentration.Changes of transition point showed that CO₂ has an inhibitory effect on soot generation.Secondly,transition point and its front and back positions were selected as transition process of soot generation,according to identified transition point of soot generation.The combustion chemistry of n-decane flame soot generation transition process was studied by combustion chemistry experiment and chemical reaction kinetics simulation combined.The results showed that increasing oxygen concentration,reducing flow rate of diluted nitrogen,and increasing fuel flow could increase flame temperature,promote formation of the main combustion products and C₁-C₄ stable intermediate products during transition process of soot generation.And experimental and simulation results showed good consistency.Increasing oxygen concentration,fuel flow rate or reducing diluted N₂ flow rate can also promote generation of soot precursors above C₄ and free radicals,and to a certain extent,peak rate of the generating reaction of these substances was increased.Finally,transition point and its front and back positions were selected as transition process of soot generation in CO₂ atmosphere,according to identified transition point of soot generation in CO₂ atmosphere.The regulation of CO₂ on transition process of n-decane soot formation was studied by comparing the results of N₂ atmosphere.The results showed that after CO₂ replaced on oxidant side and fuel side,flame temperature was significantly reduced,and production of the main products H₂ and C₁-C₄ stable intermediate products was significantly reduced,but production of CO was increased.Formation of major free radicals and soot precursors above C₄ was also significantly inhibited by CO₂ on oxidant side and fuel side.Free radicals were inhibited more significantly by CO₂ on the oxidant side,and peak rate of generating reactions from these substances were also reduced by CO₂ on both sides.