Secondary atomization of non-Newtonian kerosene gel at low Weber numbers: A numerical study

Abstract

Gel fuels are a new type of fuels with promising applications. Due to the high viscosity of the gel fuel, more attention should be paid to atomization to improve combustion efficiency. In the present paper, the secondary atomization of a non-Newtonian gel fuel has been numerically studied. The gel fuel, which is made of kerosene and fumed silica, behaves as a power-law fluid and the model parameters are determined by experimental data measured by a rotational rheometer. The volume of fluid (VOF) method is used to track the gel-air interface. The model is validated by comparing the numerical and experimental observations of the breakup process of a 1% silica kerosene gel droplet. To reveal the factors influencing the breakup of the kerosene gel droplet, a series of parametric studies were performed. The numerical results indicate that in the range of low We, the gel droplet shows bag mode and multimode, which agrees with the experimental observations. During the deformation process before the breakup, the maximum droplet diameter of the bag mode is about 2.0 to 2.5 times of the initial diameter, whereas it is more than three times for multimode. Both of the bag mode and multimode exhibit a slow deformation rate at the early stage, a constant deformation rate at the middle stage and an accelerated deformation rate at the later stage. Moreover, it is also found that there is a significant fluctuation in the deformation rate when We is close to the critical We. The dimensionless breakup time of the studied kerosene gel droplet has a linear relationship with We, but it is almost not affected by the density ratio of the droplet and the surrounding fluid.