Numerical simulations of a shock-driven n-Dodecane liquid fuel droplet

Shock-driven droplet breakup, evaporation, and reaction plays an important role in liquid fuel droplet combustion, with applications in scramjets [1], Rotating Detonation Engines (RDEs) [2], and several industrial phenomena. Liquid fuels have the advantage of ease of storage and higher energy density, making them an attractive energy source for engines. We have investigated using detailed numerical simulations, the evolution of a droplet of n-Dodecane liquid fuel, that is impacted by a strong shock of Mach 5. The simulations consider the effects of surface tension, phase change due to evaporation and chemical reactions. A phenomenological description of the complex droplet evolution will be discussed including surface instabilities contributing to deformation, stretching and ultimately breakup. Furthermore, evaporative effects induce Stefan flow which leads to cooling of the droplet surface. As the fuel vapors react, a diffusion flame is formed on the windward side, leading to intense droplet heating and enhanced vapor production in that region. In contrast, the leeward side is occupied by pre-shock gasses entrapped in a low-pressure region formed by flow separation, resulting in lower temperatures and vapor production. Our results show significant spatial inhomogeneities are present in the droplet flowfield, and must be considered in the development of reduced order models.

¹Z. X. Ren et al., Prog. In Aero. Sci., 105, 40-59, (2019)

²P. Wolanski et al., Shk. Waves, 31, 807-812, (2021)