Puffing and micro-explosion of heated droplets for homogeneous ethanol-propanol-hexadecane fuel and micro-emulsified ethanol-biodiesel-hexadecane fuel

Puffing and micro-explosion of multi-component fuel droplets induced by flash boiling of its volatile components can improve the atomization of fuel sprays and the evaporation of fuel droplets. In this study, the puffing and micro-explosion of single droplets for homogeneous ethanol-propanol-hexadecane (EPH) fuels and micro-emulsified ethanol-biodiesel-hexadecane (EBH) fuels are investigated experimentally using suspended droplets. The results show that, for homogeneous EPH fuels, the breakup mode is changed from puffing at 20 vol% ethanol-propanol concentration to micro-explosion at 60 vol% ethanol-propanol concentration; for micro-emulsified EBH fuels, the droplets undergo a micro-explosion at 20 vol% ethanol-biodiesel concentration, while a weak puffing at 60 vol% ethanol-biodiesel concentration. The micro-explosion of the two fuels is different: for EPH fuels, micro-explosion is induced by intense bubble nucleation and fast bubble growth, whereas for EBH fuels, it is induced by instantaneous vaporization of ethanol after phase separation. In addition, for EPH fuels, the bubble growth rate is enhanced at high ethanol-propanol concentration that leads to a violent breakup of bubbles, and eventually a micro-explosion of droplets. In contrast, for EBH fuels, the fuel structure is changed from ethanol-in-hexadecane to hexadecane-in-ethanol as increasing the ethanol concentration that results in the preferential evaporation of ethanol before the breakup of droplet.