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

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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