Observation of micro-explosion inside a spray flame

Although droplet micro-explosion phenomena have been intensively studied, the research on its occurrence inside a spray flame is very limited. Interesting phenomena associated with micro explosions were observed inside a spray flame in this study. First, a number of emulsified diesel were prepared with different water content. The bubbles' size of the water phase in the fuel has been measured using microscope and stability test have been conducted for all the prepared emulsions. The emulsified fuels were then injected and combusted in a constant volume vessel with optical access. High speed imaging was used for both spray and natural flame luminosity studies. The spray image demonstrated longer liquid penetration of emulsified fuel due to the low volatility of water. The natural flame luminosity images were acquired in a way that a slight overexposure of the camera to the total soot incandescence was imposed so that the lift-off region can be illuminated. It is of great interest to visualize the puffing and droplet combustion caused by micro-explosion in the spray combustion of emulsified fuel at the lift-off region under certain ambient and injection conditions. The secondary atomization, induced by the micro-explosion, has been generally considered the major reason of the decrease of pollutants from the combustion of emulsified fuel. In this study, it is found, however, that the micro-explosion could also occur on the jet liquid core and affect the primary breakup under certain conditions. Elevated injection pressure and higher water content are also found to suppress the occurrence of the primary jet breakup.