Multicomponent drop breakup during impact with heated walls

Understanding multicomponent drop breakup during impact with walls is critical to the prediction and optimization of fuel-air mixture distribution in combustion systems. In combustors, drops impact walls over a range of wall temperatures and drop velocities, resulting in complex outcomes. In this paper, the regimes of drop impact are characterized for bicomponent and multicomponent fuel drops impacting hot walls. Mixtures of n-heptane and n-decane were used to represent low and high boiling point fuel components, respectively. The wall surface temperatures were varied from 27 to 400 degrees C with drop Weber numbers ranging up to similar to 700 for a range of mixing ratios of n-heptane and n-decane. The drop impact events were recorded using high-speed imaging, allowing the identification of impact outcomes and classification into regimes of film deposition, nucleate boiling, and rebound at low Weber numbers, and splashing and breakup at high Weber numbers. In bicomponent mixtures of n-heptane and n-decane, increasing the fraction of the volatile component (n-heptane) results in secondary film breakup at low wall temperatures and a shift in the classified regimes of impact. The droplet size distribution following this secondary breakup was determined, and results show a decrease in the mean droplet size with increasing volatile concentration. Finally, commercial gasoline and diesel fuel drops were examined over similar wall temperature and Weber number ranges. The impact regimes are comparable to those identified for the well-defined bicomponent liquid mixture, in which more volatile components promote rebound and disintegration of the liquid. (C) 2019 Elsevier Ltd. All rights reserved.