Expansion and combustion of droplets that contain long-chain alcohol alternative fuels

Abstract

This paper studies the expansion, micro-explosion, and combustion behaviors of base fuels blended with long-chain alcohols. Diesel, biodiesel, and aviation kerosene are chosen as the base fuels, while n-butanol and n-pentanol are representative long-chain alcohols. Upon addition of a long-chain alcohol, deformation of the blended-fuel droplet becomes more violent. Expansion and ejection of internal liquid and gas occur throughout the process; larger proportions of long-chain alcohols lead to larger ejection holes. The degree of expansion first increases and then decreases with the proportion of alcohol. The effect of the alcohol type on d* (normalized droplet diameter) is substantial at low φ (volume fraction of long-chain alcohol) but negligible at high φ. The aviation kerosene-based fuel exhibits the smallest changes in d*. The effects of φ and the alcohol type on the micro-explosion delay time are also analyzed. The ignition delay time of the diesel-based fuel decreases monotonically with the increasing alcohol proportion and that of the biodiesel-based fuel first decreases and then increases, while that of the aviation kerosene-based fuel increases and then decreases. The combustion rate of a pure base fuel accelerates upon addition of alcohol. The ignition delay time is greatly shortened at higher temperatures, and the combustion duration shortens significantly at temperatures lower than 800 °C. The biodiesel-based fuel offers the shortest ignition delay time and the longest combustion duration, while aviation kerosene exhibits the opposite characteristics. Finally, the micro-explosion and comprehensive combustion indices are proposed to estimate the comprehensive micro-explosion and combustion performances, respectively, of blended fuels.