Splashing of a gasoline-camellia oil droplet impact on thin film-heated wall: Secondary droplets

Biomass oil has attracted extensive attention due to its carbon neutrality, high energy density, and renewable nature. During its spray combustion, the droplet impacting heated wall surfaces is of paramount significance. Despite extensive research, few studies focused on the splashing behavior of a mixing oil droplet impacting a thin film on a heated wall, particularly on transition regimes and characteristics of secondary droplets. The present work experimentally studied the splashing behavior of a mixing gasoline-camellia oil (GCO) droplet impacting its thin film on heated walls, with a focus on the secondary droplets and their energy ratio. Their kinematic features (detachment time, velocity, splashing angle) were characterized by analyzing the effects of Weber number (We), Ohnesorge number (Oh) and the wall temperature T_w. Their energy ratio was further estimated through the statistical analysis of their counts and diameters. Novel concise correlations for the detachment time and the energy ratio of the secondary droplet were respectively developed by considering We and Oh. The results show that the detachment time is primarily governed by T_w and Oh, with a minimal influence of We. Splashing angle typically ranges from 30°to 50°, while splashing velocity increases with T_w and We. The count of secondary droplets, while influenced by Oh values, increases with We, gradually converging to a constant value for increasing T_w. The energy ratio of the total secondary droplets exhibits a parabolic behavior as a function of the product of We and Oh. The results demonstrate that a 50 % mixture of the camellia oil-gasoline still exhibits good splashing behavior (secondary atomization), while the optimal mixing ratio is about 25 %. These founding get valuable insights into the heat transfer mechanism involved in the impact, gasification and combustion of GCO.