Experimental study on auto-ignition characteristics of a butanol-hexadecane droplet under elevated pressures and temperatures

Auto-ignition characteristics of a butanol-hexadecane droplet were researched under ambient gauge pressures of 5 and 10 bar and ambient temperatures of 553, 633 and 713 K. Butanol-hexadecane blends of 0%, 25% and 50% n-butanol by mass (hereafter denoted by BUT’XX′) were tested in a bilayer-structure chamber (BSC). Five sub-stages were observed, namely stable evaporation, faint partially premixed combustion, bright partially premixed combustion, diffusion combustion and droplet falling. Faint partially premixed combustion and droplet falling were observed under elevated pressures but not under atmospheric pressure. The temperature growth rate was generally different in these sub-stages. Four different temperature growth rates were found under 633 K and 5 bar, while only three different temperature growth rates were found under 713 K and 5 bar. The auto-ignition delay was negatively correlated with ambient pressure and temperature. The auto-ignition delay of BUT25 was shorter than that of BUT00 and BUT50 under 633 K and 5 bar, while the increase of n-butanol led to the increase of auto-ignition delay under 633 K and 10 bar. The auto-ignition distance reflected the transportation of fuel vapor in the auto-ignition delay. The auto-ignition distance changed in a similar manner with the auto-ignition delay.