As a contribution to the decarbonisation of domestic heating, the graduation project investigates the feasibility of the application of UV sensor technology for flame detection and flame monitoring in hydrogen-powered domestic gas boilers. The research includes empirical studies and an analytical approach to describe influences on the sensor signal strength.

The German Aerospace Centre (DLR) has in the past years been performing test runs with their experimental sub-scale combustion chambers to measure and investigate the effects of unstable combustion. Some of these investigations are focused on the heat flux to the chamber walls, changes in which can cause a significant shift in chamber wall strength and even melting, and can thus lead to structural failures. As a continuation of research regarding this phenomenon, the DLR combustion chamber version D (BKD) is used to investigate changes in heat flux, and its test data have been made available for this research. Using the test data, finding a relation between measured steady state heat flux and controlled chamber conditions became feasible, and changes in heat flux related to combustion instabilities can be identified. However, although these changes in heat flux are often observed and are described in literature as a known effect of combustion instabilities, there are currently no validated explanations as to why these effects take place. In an effort to provide this explanation, the results of a previously completed investigation regarding the DLR combustion chamber version H (BKH) are evaluated, as they allowed determination of a relation between combustion length and magnitudes of acoustic pressure oscillations. In this research, the results obtained for combustion length are converted to a model regarding varying heat flux profiles and modified as to implement them for BKD. Finally, the model predicted increases in heat flux during time periods when increases are observed experimentally, showing agreement with the experimental data. Besides this, a conversion in the model allowed reconstruction of a localised heat flux profile, which showed an increase in local heat flux near the injector face plate. This matches effects described in literature and observed in the experimental set-up after a test run with combustion instabilities. With this validation of the model, the theory developed and tested in this thesis work could prove a significant advancement in the understanding of effects of combustion chamber instabilities and their impact on the engine integrity and performance.

Optical measurement techniques are widely used in fluid mechanics to measure quantities like velocity, vorticity, and temperature. They are usually non-intrusive visualization techniques that provide a major advantage by not influencing the flow properties. Most of the developed measurement techniques estimate vorticity by computing the gradients of the measured velocity fields. In this project, the idea is to directly measure the mean vorticity using polarized emission of nanoparticles. The nanoparticles are excited using vertically and horizontally polarized laser. Accordingly, the emission from these nanoparticles is separated into vertical and horizontal polarized emissions respectively. Depending on the percentage of fluorophores in the nanoparticles whose absorption dipole moment is parallel to the excitation electric vector of the laser, the polarized emission is varied. The nanoparticles in the quiescent fluid state have a characteristic polarization (or anisotropy) depending on the chemical composition of the nanoparticle. However, in turbulent flows, depolarization of the particles can occur because of the rotation of the nanoparticles due to vorticity. Based on this idea, the vorticity can be estimated by quantifying the depolarization in turbulent flows. To verify the above phenomena experimentally, steady-state polarization measurements were conducted. An experimental setup was built specifically to measure depolarization from these nanoparticles. Important preliminary tests like lifetime measurements, spectroscopic studies, and photo-bleaching experiments were conducted. Based on these results, hybrid europium based chelated spherical particles were chosen. To further understand the properties of these particles in a quiescent flow, a consolidated set of anisotropy measurements were conducted to study their oxygen sensitivity in the surrounding medium, viscosity dependence and the effect of its concentration in the fluids. Analytical correlations which was developed in-house to translate the depolarization of the nanoparticles to vorticity was used in this thesis. Flow in a square duct was studied to estimate the vorticity along the edges and further compare it with the DNS data.
Two additional non-dimensional numbers ND1 and ND2 were introduced to interpret the underlying physics behind the problem. The variation of synthetic signals was studied for different Re, fundamental anisotropy r0 and the non-dimensional number ND2. These synthetic signals showed a drop in anisotropy near the edges of the square duct that has occurred probably due to vorticity. Emission polarized intensity signals and the anisotropy contours for Re = 0 and Re = 4434 were analyzed. Due to the measurement error, the contours were column averaged and respectively compared their variation along the width of the square duct. A drop in anisotropy was observed for Re = 4434. Using the ratio of emission intensities for each excitation polarization, the vorticity was estimated using the optimization algorithm. The estimated vorticity Ѡy shows similar trends compared to DNS data which is a promising evidence for the proof of concept. However, the results are not overlapping from the repeatability studies due to the high sensitivity of the optimization algorithm and the random error from the measurement equipment. To improve this technique in the future, transient experiments have to be conducted to estimate vorticity accurately and to capture the underlying physics.

Research on laser communication technology for satellites has led to a sufficient understanding of this technology to start working on commercial applications. In this work a design is proposed for a lasercom system for CubeSats, a type of nanosatellites that is used increasingly often for commercial missions. The goal of this design is to offer substantially higher datarates from low earth orbit to ground compared to radio links, without regulatory constraints and at competitive costs. To support the first-order design as proposed in this work, a detailed implementation is described. One component of this design, the sensor that accurately measures the angle of the incoming light, is analysed experimentally.

NOx emissions cause harm to the human body, the world around us and our atmosphere, both directly and indirectly. Flameless combustion is a combustion regime that has the potential to reduce these emissions by more than 95%. Operation in this regime is possible when lowering the availability of oxygen and lowering the combustion temperature in the combustion zone. Key for this operation is the recirculation of flue gases using internal recirculation zones and mixing of these gases with the incoming combustion air and fuel. These aerodynamic characteristics have been researched experimentally and numerically for the DUT flameless combustor. Results show recirculation and mixing can be increased with decreasing the jet size, however with an increase pressure loss. Numerical investigation shows that simulation of this setup is challenging using RANS and that LES might be the only way to go forward.