Mechanism and Safety Aspects of Shock Induced Explosions of an Oxygen Containing Bubble in a Flammable Liquids

摘要

Shock induced ignition of oxygen containing bubbles in liquid cyclohexane, methanol, 2-ethylhexanal and cumene is theoretically investigated. An important experimental fact is that the ignition took place not only when the bubble contained initially an explosive gas mixture, but also in the case of an initially non explosive fuel-lean gas mixture. The explosion of these initially non explosive gas mixtures was observed in 2-ethylhexanal and cumene. It is shown theoretically, that fuel evaporation in a bubble, caused by mechanical mixing of surrounding liquid with the gaseous phase in the bubble (cumulative jet penetration into bubble and subsequent dispersion and evaporation of micro-droplets) can increase the fuel vapor concentration in a bubble essentially, in effect shifting the chemical composition from outside to inside the flammable range. This process together with the simultaneous increase of gas pressure and temperature during a shock induced bubble compression explain the experimental observation of ignition in bubbles of an initial fuel-lean gas composition.Calculation of the explosion limits of a single bubble has been performed. The possibility of explosion of a preliminary compressed bubble due to interaction with a spherical shock wave emitted by a nearby exploded bubble has been theoretically investigated.Measurements of flammable characteristics of gases at elevated parameters (auto-ignition temperature and flammable limits), based on experimental observation of shock induced bubble explosions and Rapid Compression Machines measurements are compared.