Title of Paper:Mechanism of micro-explosion of water-in-oil emulsified fuel droplet and its effect on soot generation

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Date of Publication:2020-01-15

Journal:ENERGY

Included Journals:EI、SCIE

Volume:191

ISSN No.:0360-5442

Key Words:Micro-explosion; Droplet breakup; Emulsified fuel; Combustion

Abstract:In this study, the mechanism of micro-explosion of single droplets of water-in-oil (W/O) emulsified fuels and its effect on the soot generation are investigated experimentally using suspended droplets. Two distinct breakup modes are observed as the droplets are heated, namely catastrophic micro-explosion after water coalescence at a lower surfactant concentration and puffing at a higher surfactant concentration without water coalescence. To understand the underlying physics of such transition, the water/oil interfacial tension is investigated. It is found that the increase of water/oil interfacial tension after the deactivation of surfactant can significantly accelerate the coalescence of dispersed water, and effectively increase the temperature of bubble nucleation. The deactivation of surfactant is a prerequisite for the occurrence of catastrophic micro-explosion. The reason is found to be that the catastrophic micro explosion can be induced by the explosive vaporization of water only if the dispersed water coalesces rapidly into large droplets to explode violently at a high superheat degree. The surfactant concentration in emulsified fuels influences the deactivation temperature of surfactant. Therefore, the catastrophic micro-explosion can be controlled to occur by adjusting the surfactant concentration in emulsified fuels. In addition, it is also found that the micro-explosion of W/O emulsified fuel during the combustion can effectively decrease the soot generation due to uniform fuel/air mixture formed after the microexplosion. (C) 2019 Elsevier Ltd. All rights reserved.