Equivalence ratio inhomogeneity and mixing in liquid-fueled detonations

Liquid-fueled detonation systems are intrinsically heterogeneous due to the discrete nature of liquid droplets, and their initial size and spatial distribution. Understanding the effect of droplet spatial distribution perturbations coupled with droplet-scale effects like lag, breakup, and evaporation is essential in predicting realistic multiphase detonation phenomena. In this paper, the effect of initial perturbations of equivalence ratio, created by a 2D sinusoidal spatial distribution of uniform sized droplets, on the detonation behavior is examined through 2D Euler-Lagrange simulations. The propagation speed and cellular structure of detonation propagating through a tube with Decane droplets suspended in air (N2/O2 mix) is simulated using a quasi-global 3-step 7-species reaction mechanism. The effect of small-scale fluctuations in fuel concentration, due to random particle positions, is found to be of minor importance compared to the large-scale perturbation produced by the sinusoidal spatial distribution. Increased initial inhomogeneity decreased the detonation speed, made the detonation more unstable, and caused an overall increase in cell size. The extent/strength of inhomogeneity that a multiphase detonation can overcome is found to be much lower than that of an equivalent gaseous detonation.