Unsteady Interaction Between Laminar Propagating Flame and Array of Small Fuel Droplets

实验研究了燃料液滴阵列或单个燃料液滴在层流平坦火焰作用下恒压通过稀薄均质丙烷/空气混合物的着火过程。测试了由正己烷和正十六烷或正十二烷以及苯和正十六烷组成的二元燃料。还使用了由正十二烷组成的水乳化液，以及正己烷、正辛烷、正十二烷和正十六烷等纯燃料。由透明管道制成的燃烧室安装了火花电极、悬浮燃料液滴的细石英纤维，以及允许燃烧的气体从顶端泄漏的百叶窗。采用高速摄像机对燃烧火焰点燃的每个液滴进行了摄影观测，纯燃料液滴的着火延迟期随初始液滴直径的增大和燃料挥发度的减小而单调增加。初始液滴直径对点火延迟期的影响随…的增大而减小更多的燃料波动。混合燃料液滴的着火延迟随高挥发分燃料体积浓度的增加而减小。两种燃料的着火延迟随初始液滴直径的变化呈现出最小和最大值。随着高挥发分燃料浓度的增加，着火延迟期的最小值和最大值直径减小。点火延迟或乳化燃料液滴与预期的初始液滴直径单调。与燃料的二元混合物相比，高挥发性组分的体积浓度的增加导致了相反的结果，因为在这种情况下，高挥发性组分是水。液滴后面传播的火焰的一部分在经过液滴或挥发度较高的燃料时向未燃烧的气体凸起，而对于挥发度较低的燃料，火焰保持不变。随着高挥发分燃料浓度的增加，液滴后传播火焰的变形长度增大。较少

An experimental study has been made of the ignition process of fuel droplet array or single fuel droplets subjected to a laminar flat flame propagating through a lean homogeneous propane/air mixture at constant pressure. Binary fuels consisting n-hexane and n-hexadecane or n-dodecane, and benzene and n-hexadecane were tested. Water-emulsified liquids consisting n-dodecane, and pure fuels like n-hexane, n-octane, n-dodecane and n-hexadecane were used as well. A combustion chamber made of a transparent duct was installed with spark electrodes, fine quartz fibers to suspend fuel droplets, and a shutter to allow the burned gas to escape at the top end. A high-speed video camera was provided for photographic observation of each droplet ignited by the propagating flame.Ignition delay of pure-fuel droplets increased monotonically with increase of the initial droplet diameter and decrease of fuel volatility. The influence of the initial droplet diameter on ignition delay decreased with increas … More ing fuel volatility. Ignition delay of the binary-fuel droplets decreased with increase of the volume concentration of the higher-volatility fuel. Ignition delay of the binary fuels showed a minimum and a maximum as a function of the initial droplet diameter. The diameters at the minimum and the maximum of ignition delay decreased with increasing higher-volatility fuel concentration. Ignition delay or emulsified-fuel droplets monotonically with the initial droplet diameter as expected. The increase in the volume concentration of the higher-volatility component caused an inverse result in comparison with that for the binary mixtures of fuels, since the higher-volatility component was water in this case. Part of the propagating flame behind the droplet became convex towards the unburned gas as it passed a droplet or higher-volatility fuels, while the flame remained flat for the lower-volatility fuels. The deformation length of the propagating flame behind the droplet increased with increasing higher-volatility fuel concentration. Less