The secondary atomization behavior and spray flame characteristics of carbonated W/O emulsified fuel were studied. The dissolved CO2 in the carbonated emulsified fuel was able to reduce the bubble nucleation energy needed for secondary atomization. First, the spray characteristics of carbonated fuels were studied in a N-2 environment at 923 K, using high-magnification shadow imaging of the spray droplets. This allowed the spray droplets to be clearly visualized during secondary atomization. The dissolved CO2 was shown to enhance secondary atomization by decreasing the bubble nucleation energy, resulting in the production of finer spray droplets. The spray flame characteristics of n-dodecane,emulsified fuel, and carbonated emulsified fuel were then studied in a laminar counterflow burner. Direct photography of the flame using a color high-speed video camera and magnified shadow imaging using a monochrome high-speed video camera were used. Compared the ignition point of luminous flames in n-dodecane, an ignition delay was found in the emulsified fuel, which was not found in the carbonated emulsified fuel. Compact luminous flames were also formed in the carbonated emulsified fuel. In the magnified flame images, bright spots of higher luminosity than the surrounding area were observed in both the emulsified fuels. These proved to be a useful marker for secondary atomization. In the carbonated emulsified fuel, the bright spots appeared earlier, indicating that the dissolved CO2 reduced the droplet temperature at which secondary atomization occurred. This effect countered the ignition delay caused by water addition in the emulsified fuel. A higher frequency of bright spot occurrence was also found in the carbonated emulsified fuel. It was demonstrated that carbonation of emulsified fuel improved the spray flame characteristics through the enhancement of secondary atomization. (C) 2016 Elsevier Ltd. All rights reserved.