Investigation of evaporation and combustion characteristics of diesel and fatty acid methyl esters emulsified fuel droplets

Abstract

To address the problems of energy shortages and environmental pollution, biodiesel and its emulsified fuel have gained wide attention. In this work, the fatty acid methyl esters (FAME) emulsified water-in-oil fuel (BW) is thoroughly investigated using the droplet suspension experiment with a focus on the main characteristics of puffing/micro-explosion, droplet ignition delay and flame regime, etc. The role of water content at different ambient temperatures is examined in comparison to a counterpart blend of diesel/water (DW) fuel. Results show that the increase in water content and temperature has a significant promotion effect on the strength and number of puffing/micro-explosion process, however, the higher viscosity of BW leads to the lower values. And owing to the heat absorption by water evaporation, only the micro-explosion with high intensity induced by water nucleation has a favorable effect on the evaporation rate. There exists a critical concentration of water addition, after which the enhancement of evaporation is expected. Moreover, it is indicated that the diesel with water additives has a better atomization effect, and the size of child droplets generated by DW droplets breakup is smaller, which is in the range of 0.08–0.1 mm compared to the 0.09–0.13 mm for BW droplets. It has been shown that the increase in water content hinders the rise of droplet flame temperature, extends the ignition delay time, and shortens the maximum premixed-flame length. Compared to diesel droplets, the larger combustion rate of BW droplets is correlated with their shorter flame length and the higher boiling point of FAME.