For possible reduction of carbon dioxide (CO2) and soot emissions, blended diesel/biodiesel/bioethanol fuel is investigated in this study. It is known that such a fuel mixture exhibits particular behavior such as puffing/ microexplosion, or secondary breakup, depending on the mixture ratio. This study aims to identify the detailed characteristics of puffing/microexplosion and fuel vapor mixing of the blended fuel by direct numerical simulation (DNS), which captures the dynamics of all the liquid/gas and liquid/liquid interfaces. Cases are studied where a single or multiple oil droplets with internally embedded ethanol sub-droplets are placed in a hot convective air environment. The number and location of vapor nucleation, i.e. boiling vapor generation from the embedded ethanol sub-droplets, are varied to characterize the difference in the degree of secondary breakup and mixing. The ethanol vapor is initially contained inside the parent oil droplet, and soon it is ejected outside. Secondary breakup occurs by this vapor ejection. Later, the ethanol vapor further spreads into the mixture of surrounding oil vapor and air. Gas-phase ethanol/oil/air mixing is characterized by the scalar dissipation rates (SDRs). The magnitudes of SDRs become intense in a region where mixing is enhanced between the ethanol and oil vapors due to the high-speed ethanol ejection. If the vapor ejection direction is inclined toward the crossflow direction, its flow field becomes similar to that of a jet in crossflow. The penetration trajectory can be predicted by the correlation of 1/3-1/2 power law. This trajectory temporarily influences the effective inter-droplet distance in multiple-droplet cases even if the geometrical distance l is unchanged, which is important for the group combustion concept. In a multiple-droplet case, the mode transition from separated droplets to grouped droplets has been observed in the crossflow direction. Such information is significant in modeling the group combustion in a fuel spray of blended multiple fuels.