Impact of atomization on particle synthesis in spray flamesWSA
An essential part in the process of spray flame synthesis of nanoparticles is the atomization of precursor solutions. This provides the droplet phase, whose characteristics are a crucial initial condition for the subsequent evaporation, turbulent mixing, and combustion. Through this, the atomization process directly or indirectly influences local conditions in the spray flame including temperatures, gas compositions, velocity fluctuations, and residence times. The local conditions in turn determine the individual mechanisms leading to particle synthesis, and consequently, there is a direct link between the atomization close to the nozzle and the properties of the final nanoparticles. Despite of this, the influence of the injection system and the properties of the primary droplet phase on spray flame synthesis have not been sufficiently investigated, and only few studies with partly contradictory findings are available in the literature. This is mostly because of the fact that primarily coaxial atomizers have been used in previous studies, which do not offer the possibility of a broad variation of the characteristics of the primary droplet phase. However, such variations are an important prerequisite for developing a sound understanding of the entire particle-generation chain. For given process conditions, the configuration of the atomizer is one of only few possibilities to control and to optimize the final product quality. This fact underlines the importance of the questions considered in the present proposal. The aim of this research project is to provide a fundamental understanding of the influence of atomization on particle formation in turbulent spray flames. Specifically, the goals are to clarify whether and how a change in characteristics of the primary droplet phase influence the local conditions of the reaction of the spray flame and how these conditions affect the individual steps in the process of particle formation. An essential means for the analysis of these interrelations is a wide and systematic variation of the primary droplet dynamics. Such a variation is not possible by just using the nozzle specified in the SPP 1980. Therefore, within the proposed research, different types of atomizers (full cone nozzle, hollow cone nozzle, swirl nozzle) shall be used and adapted to the SpraySyn burner. In this way, not only the average drop size can be influenced, but also the spatial distribution of the droplet number density, the droplet size, and the droplet speed. The collaboration of three research groups from different disciplines allows for a detailed experimental and numerical investigation of important mechanisms (inner nozzle flow, atomization, particle formation, etc.) along the entire process chain.
DFG, SPP 1980
- Prof. Heinz Pitsch, Institut für Technische Verbrennung der RWTH Aachen
- Prof. Hans-Joachim Schmid, Lehrstuhl für Partikelverfahrenstechnik, Universität Paderborn