Optical Diagnostics of Reactive Flows : Application of 3D emission tomography and laser-based methods

Sammanfattning: Nowadays, numerous specialized systems, ranging from electronics to energy production processes can be found both in science and industry. However due to their specialized nature they often exhibit high sensitivity to intrusive measurements, which can potentially perturb the sought-after characteristics or quantity and consequently compromise overall accuracy. In these scenarios, optical measurements can offer a potential solution owing to their often-non-intrusive nature based on the photon-in-photon-out concept. The application of different optical techniques does not only enable the achievement of non-invasiveness but can also offer the capability to measure and quantify observable phenomena that may not always be accessible through conventional probing methods.The work within this thesis centers on three-dimensional (3D) emission tomography and its application in the context of reactive flows. Many reactive flows, such as those found in combustion processes, inherently exhibit three-dimensional characteristics, benefitting from measurement techniques that can perform measurements in all three dimensions. The work covers the fundamentals of emission tomography and showcases the techniques application in both combustion and plasma research. The application in combustion diagnostics yielded volumetric flame reconstructions and investigated the use of arbitrary sensor positions to overcome limitations in optical access. Similarly, plasma diagnostic application allowed for volumetric gliding arc reconstructions facilitating quantification of 3D characteristics such as 3D arc length and arc volume. This is followed by stereoscopic 3D particle tracking applied in iron combustion, looking at particle micro explosions and 3D velocities.Subsequently, various optical laser-based techniques applied in the work within this thesis are presented, each accompanied by an experimental application. These techniques include particle image velocimetry (PIV), for flow field analysis, and laser-induced fluorescence (LIF), for hydroxide (OH) analysis, both applied in a model lab-scale gas turbine swirl combustor. Additionally, fluorescence lifetime imaging (FLI) was utilized in gliding arc plasma investigations in combination with 3D emission tomography to investigate OH fluorescence lifetimes.Investigation of potential nanoparticle release during iron combustion was carried out using shadowgraphy, enabling the visualization of release trails produced by individual iron particles. Moreover, work within phosphor thermometry was performed, investigating the impact of PMT non-linearity effects on measured phosphorescence lifetimes and applied for in-situ surface temperature measurements on heat exchanger pipes in a multi-fuel Stirling engine.