Experimental Investigation of Microexplosion Phenomena in Emulsified Vegetable Oil-Methanol Blends

Secondary atomization is one of the most attractive and misunderstood effects in the combustion of microemulsified fuel blends. The occurrence of secondary atomization has been studied to determine its effects on improved combustion efficiency especially when low vapor pressure fuels are used. Several methods to detect microexplosion as alternative to secondary atomization have been considered including acoustic signal processing. As part of the physical characterization of an emulsified vegetable oil-methanol blend, microexplosion behavior of fuel blend droplets has been observed to take place under certain environmental conditions. Droplets microexplode as methanol surrounded by vegetable oil molecules flashes or microexplodes under intense temperature and intense droplet pressure. The droplets of emulsified methanol-in-oil break up forming tiny droplets with greater surface-to-volume ratio in the process. To understand the effects of emulsification on microexplosion, characterization of secondary atomization has been performed using a temperature probe, a high-speed camera and an acoustic sound signal processor. Experiments have been conducted at temperatures similar to those encountered in liquid fuel boilers. The acoustic signal data were analyzed using Fast Fourier Transform (FFT) to define and understand the overall microexplosion process. Also, the effect of temperature, droplet sizes and the percentage of methanol in the vegetable oil blend have been studied to understand what leads to a higher probability of microexplosion occurrence. A correlation between the analyzed acoustic signal data and high speed images were used to differentiate between the different microexplosion events. The results of the study can be useful in predicting the occurrence of microxplosion in liquid fuel boiler which should result in more complete combustion processes, reducing contaminant levels significantly.