Image-based in-situ Diagnostics in the Spray Flame Synthesis of Nanoparticles

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In-situ diagnostics imaging is a necessary tool to for the quantitative visualization and a better understanding of the processes taking place in spray flame synthesis, and provide valuable data for validations of chemical-kinetic models and fluid-dynamic simulations of the underlying gas phase and particle formation pathways. The aim of this project is the quantitative (mostly laser-based) single-pulse imaging diagnostics of temperature, intermediate species concentration and particle in the standardized SpraySyn burner under the harsh conditions of spray flame synthesis (turbulent reactive flow, presence of droplets and / or particles). Besides temperature for the liquid and gaseous phase, the measurements concentrate on important chemical intermediate species (progress variables) relevant for model development and simulation of the global particle synthesis process performed in other SPP research groups. Fundamental spectroscopic investigations (excitation/fluorescence spectra, fluorescence lifetimes) of individual atomic / molecular species in a flow system should initially define optimal excitation / detection strategies for later quantitative laser-induced fluorescence (LIF) imaging. Imaging of gas phase temperatures is then performed by single-pulse two-line LIF thermometry on molecular tracers such as NO (external admixture to the fresh gases) or e.g. OH, BaO or Fe (present as a reactive intermediate) in the SpraySyn flame. The instantaneous temperature values then also provide flame statistics in the form of mean values, standard deviation and histograms of the measured scalars. Similar quantities are determined with concentration values of various important intermediates such as OH, Fe, FeO, or Ba recorded in their electronic ground states by two-color single pulse LIF. The combination of two independently tunable laser wavelengths and two camera detectors enables correlated measurements of concentration fluctuations by the simultaneous detection of two different species, e.g., a fuel marker and intermediates indicating the presence of fuel and an intermediate product of precursor decomposition in the probe volume. In addition to the gas phase, planar single-pulse temperature imaging of the liquid phase (fuel jet, droplets) will be carried out for the first time using the two-color LIF method by adding non-evaporating dyes (coumarin, rhodamine). The particle clouds are visualized qualitatively via Rayleigh scattering or laser-induced incandescence (LII), and statistical correlations with reactive species (via LIF) are determined. All results will contribute to further extending the already existing SpraySyn database. This not only provides validation data for projects modeling the processes, but also supports the project Mohri in comparing with results of their tomographic reconstruction of flame chemiluminescence and particle distribution, as well as the project Kaiser dealing with the microscopic examination of drop explosions.