Experimental and numerical investigation of the binary droplet-film-interaction

• Applicants: Dr.-Ing. Grazia Lamanna; Professor Dr.-Ing. Bernhard Weigand
• Subject Area: Technical Thermodynamics
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 284229203

The study of single droplet impact onto thin wall-films of a different liquid (two-component droplet wall-film interaction) has a great number of industrial applications. One example is the reduction of emissions in diesel engines by late post-injections. During post-injection diesel droplets can impinge onto the lubricating oil film, covering the combustion chamber walls. It is here that a better understanding of the two-component splashing dynamics can be beneficial for the minimization of engine emissions. To gain a better understanding of the underlying physics, the influence of the liquid properties on the dynamics and the mixing process during the interaction needs to be investigated. In the first funding period, considerable progress was made in the understanding of two-component droplet wall-film interaction. Nevertheless, many questions still remain unanswered with respect to the generalization of the results to different fluids and to realistic engine conditions. Both aspects are investigated in the present proposal that comprises both an experimental and numerical part.Experimentally, a thorough investigation is foreseen to analyze the effects of liquid properties on the crown topology (e.g. shape, height, number of fingers etc.) and on the distribution of secondary droplets (number, size and velocity) formed during impact. For this purpose, both the liquids viscosity and surface tension are varied systematically. These experimental findings, supported by theoretical considerations, will then be employed to derive a generalized semi-empirical model, capable of describing the impact process of two-component droplet wall-film interactions. The numerical simulations, instead, will focus on the analysis of the mixing process upon drop impact. Special emphasis will be given to the understanding of the mechanism responsible for the formation of holes in the crown wall, which is a specific feature of two-component interactions. Concerning the extension to realistic chamber conditions, two aspects are considered: heated wall chambers and non-Newtonian effects. The former is investigated mainly experimentally by employing a heatable wall-film generation system. Changes in liquid properties due to temperature variations will be characterized and compared to the results of the previously performed investigations. The influence of non-Newtonian liquid properties on the two-component droplet wall-film interaction will be investigated numerically. In both cases, the results from this analysis will be included in the generalized semi-empirical model.

• DFG Programme: Research Grants