Effects of Turbulence on the secondary breakup of droplets in diesel fuel sprays

Abstract

In this paper, the importance of turbulence effects on the procedure of droplet’s secondary breakup is studied. In the process of modeling the secondary breakup of a droplet, it is a common practice to presume that the droplet is moving in a laminar flow. However, it is evident that the critical Weber number is profoundly affected by the intensity of turbulence presented in the flow. As a result, the abovementioned supposition may lead to significant computational inaccuracy. This paper tends to perform a modification that considers the effects of turbulent flow on the secondary breakup of droplets. It is shown that the results obtained by the modified model are more precise and in a better agreement with experimental data. In this paper, spray behavior is predicted by a conventional breakup model and the one obtained by a modified model, which are both implemented in an in-house computer code. This CFD code accounts for engine simulation by solving the governing two-phase-flow equations using the Eulerian-Lagrangian approach in a three-dimensional coordinate system. To show the effects of turbulence, the changes in spray parameters such as droplet size distribution, spray tip penetration, and spray mean diameter, which is extracted from the two models are compared. Results have shown that the turbulence causes droplets to break in an earlier time, which leads to a higher rate of evaporation and lower penetration length. An interesting fact concluded in this paper is that the difference between the results of the two models decreases as the gas pressure is increased, which means the effects of turbulence become less important as the gas pressure increases.