Influence of atomization on particle synthesis in spray flames

前驱体溶液的雾化程度对喷雾火焰合成纳米颗粒有重要影响。喷嘴附近的特征液滴和气相是在火焰中形成沿颗粒形成轨迹的局部合成条件的必要输入条件。因此，雾化的任何变化都会直接影响到颗粒的性质。在这种情况下，喷嘴的设计代表了一个基本的自由度，可以用来更好地了解喷雾火焰和颗粒形成机制的耦合，并在此基础上实现对颗粒特性的长期有针对性的控制。喷嘴几何形状对喷雾火焰合成的高度重要性通过本项目第一阶段的工作得到证明。结果表明，不适当的雾化可能会导致不希望看到的火焰脉动。由于这种脉动阻碍了对喷雾特性对颗粒形成过程链的影响的严格调查，因此开发了一种改进的雾化器设计，显著减少了火焰脉动。在此基础上，通过数值模拟和实验研究，定性和定量地研究了雾化器设计对颗粒尺寸分布的影响。然而，还需要进一步的研究来澄清喷雾特性和颗粒特性之间是否以及在哪些条件下存在直接关联。基于这一认识，本研究项目旨在通过有针对性地改变喷雾特性和高分辨率的实验和数值方法，从根本上理解局部合成条件对喷雾火焰形成机制的影响。在这方面，我们将量化个别喷嘴相关的雾化过程和随后的液滴-火焰相互作用如何以及在多大程度上影响局部反应和合成条件的形成。在此基础上，将对颗粒形成机制和喷雾火焰机制之间的相互敏感性有一个基本的了解。将引入和使用新的雾化器设计，允许通过对喷雾特性的特定操作来系统地改变相关的喷雾火焰机制。

The spray flame synthesis of nanoparticles is significantly influenced by the atomization of the precursor solutions. The characteristic droplet and gas phase in the vicinity of the nozzle is an essential input condition for the formation of local synthesis conditions in the flame along the trajectories of particles during their formation. Thus, any change of the atomization will directly affect the particle properties. In this context, the nozzle design represents an essential degree of freedom, which can be used to gain a better understanding of the coupling of spray flame and particle formation mechanisms and, on this basis, to enable a targeted manipulation of particle properties in the long term.The high importance of the nozzle geometry for spray flame synthesis was demonstrated by work in the first phase of the current project. It was revealed that an unsuitable atomization can lead to undesired flame pulsations. Since such pulsations prevent a rigorous investigation of the influence of spray characteristics on the process chain of particle formation, an adapted atomizer design was developed which significantly reduces flame pulsations. On this basis and with the help of numerical and experimental investigations, it was shown qualitatively and quantitatively that the particle size distribution can be significantly affected by the selected atomizer design. However, further research is needed to clarify whether and under which conditions a direct correlation between spray characteristics and particle properties exists. Furthermore, it is unknown how the responsible individual mechanisms of particle formation are influenced by the nozzle-dependent local synthesis conditions along the trajectory.Based on this knowledge, this research project aims to provide a fundamental understanding of the influence of local synthesis conditions on spray flame mechanisms by means of a targeted variation of spray characteristics and high-resolution experimental and numerical methods. In this context, we will quantify how and to what extent the formation of local reaction and synthesis conditions is affected by individual nozzle-dependent atomization processes and subsequent droplet-flame interactions. On this basis, a fundamental understanding of the mutual sensitivity of particle formation mechanisms and spray flame mechanisms will be achieved. New atomizer designs will be introduced and used, which allow a systematic variation of the relevant spray flame mechanisms by a specific manipulation of the spray characteristics.