Puffing and Microexplosion Behavior of Water in Pure Diesel Emulsion Droplets During Leidenfrost Effect

Abstract

The microexplosion evolution phenomenon of single droplets of water in pure diesel emulsion under Leidenfrost effect has been studied. The tested emulsions were stabilized with a blend of commercial surfactants with three different water contents of 9%, 12% and 15%. A high speed camera synchronized with backlight technique was used to capture the evolution of microexplosion and puffing. Three different droplet diameters of approximately 2.6mm, 2mm and 0.2mm were analysed. It was found that the tendency of microexplosion and puffing frequency was influenced by the droplet diameter. Coalescence was the dominating factor in inducing microexplosion in bigger droplets. It was observed that the child droplets ejected from the parent droplet undergoes further puffing processes.The size of the secondary droplets after microexplosion were also found to be slightly influenced by the parent droplet size.The waiting time for microexplosion and puffing were compared for different droplets size.

Experimental investigation on puffing and micro-explosion occurrence of water in rapeseed oil emulsions droplets. Effect of the surfactant concentration.

“…For each set, bigger vapor bubbles are observed in a shorter period of time for emulsions without surfactant. In this regard, comparable results have been attained for other emulsified fuels [10][11][12], in spite of the effect of additional factors such as the surfactant percentage, the analyzed size of the emulsion droplet and characteristics of continuous phase (e.g. volatility, viscosity, carbon-chain length, etc.)…”

“…The emulsion fuel drops are placed on a heated plate leading to the Leidenfrost effect. Recently, several researches have been conducted in this topic using Leidenfrost burning [11,[14][15][16]22]. A pipettor VWR with tip ejector (volume: 2-20 µL, precision: ≤1.5-0.3% and accuracy of ±1.0-0.6%) is used as a fuel droplet generator.…”

“…An important factor affecting the micro-explosion could be the coalescence or phase separation of the dispersed water droplets into the continuous phase [8,10]. On the other hand, several studies [11,[14][15][16][28][29][30][31] reported the occurrence of a particular phenomenon (i.e. puffing or bubbling) prior to micro-explosion phenomenon.…”

“…However, it is important to point out that the physicochemical properties of emulsified fuel play a decisive role. Nevertheless, a large scientific effort has been devoted to the experimental evaluation of the microexplosion phenomenon [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, the micro-explosion phenomenon has been also questioned [27].…”

The Effect of Fuel Injection Equipment of Water-In-Diesel Emulsions on Micro-Explosion Behaviour

“…Micro-explosion is a very fast process, and hence the Leidenfrost technique is often used to facilitate the observation of the fast evaporation of the droplet [25][26][27][28]. Under Leidenfrost conditions, heat transfer by conduction is the dominant mode, and causes a rapid evaporation of the droplet.…”