Abstract
A new analytical solution to the onedimensional transient heat conduction equation in a composite spherically symmetric waterfuel emulsion droplet, suspended in a hot gas, is obtained. The Robin boundary condition at the surface of a droplet and conditions at the fuelwater interface are used. A water subdroplet is assumed to be located at the centre of a fuel droplet, the radius of which was fixed at each time step; it could change at the next time step. The Abramzon and Sirignano model is applied for the approximation of the droplet evaporation process. This solution and the evaporation model are incorporated into a numerical code in which droplet heating/evaporation and the variable thermophysical properties are accounted for. The time instant at which the temperature at the fuelwater interface became equal to the boiling temperature of water is identified with the initiation of puffing, giving rise to microexplosion. This allowed us to compute the minimal microexplosion delay time. The new solution is applied to a typical case of puffing/microexplosion of water/diesel emulsion droplets in high temperature gas. It is shown that the new model allows us to understand better the underlying physics of the processes leading to puffing/microexplosion. The experimental observations of the microexplosion delay time for various initial droplet sizes are shown to be compatible with the predicted values of this time. It is shown that puffing/microexplosions are expected well before the droplet surface temperature reaches the boiling temperature of ndodecane. The numerical code can be potentially implemented into Computational Fluid Dynamics codes, which can be applied to the modelling of other fuel and water/fuel blends.
Original language  English 

Article number  119208 
Number of pages  21 
Journal  International Journal of Heat and Mass Transfer 
Volume  149 
DOIs  
Publication status  Published  24 Dec 2019 
Keywords
 ndodecane
 droplet heating
 heat conduction equation
 microexplosion
 puffing
 diffusional entrapment
 boiling
 Droplet heating
 Diffusional entrapment
 Microexplosion
 Boiling
 Ndodecane
 Heat conduction equation
 Puffing
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Sergei Sazhin
 School of Arch, Tech and Eng  Professor of Thermal Physics
 Advanced Engineering Centre
Person: Academic