Development and Application of Laser-Induced Emission Techniques for Combustion Diagnostics -High-Resolution Visualization of Turbulent Reacting Flows

Abstract: Nowadays, more than 90% of our energy comes from combustion processes. Hence, it is very important to perform combustion research to reduce emissions, improve efficiency, find clean and renewable fuels, strengthen safety, etc. The complexity of combustion processes asks for advanced diagnostic tools, among which the laser spectroscopy has been proved to be a powerful one. This thesis is about the application and development of laser-induced emission techniques for combustion diagnostics. Different laser techniques have been adopted, i.e., laser-induced fluorescence (LIF), laser Rayleigh scattering, and laser-induced phosphorescence (LIP). Brief descriptions of these techniques and the main equipment used are given in the thesis. The first part of the thesis deals with application of laser techniques in turbulent combustion. The high spatial resolution of planar LIF (PLIF) and Rayleigh thermometry were performed in premixed and partially premixed laboratory flames. Visualization of flame fronts by CH2O, CH, and OH PLIF as well as temperature fields were achieved to study the interaction between turbulence and chemistry. Simulated results were used to explain the combustion phenomena, and the experimental results were analyzed for model validation The second part focuses on the development of the combustion apparatus and diagnostic techniques. A novel burner, featuring a multi-jet structure, was developed as a temperature calibration source. We can easily achieve a wide range of temperatures from ~1000 K up to ~2000 K in the burned gas region of the burner, which were measured by Rayleigh scattering. Another development is on the Heat Flux burner. By application of LIP technique instead of thermocouples (TC), the temperature distribution along the radius of the burner perforated plate was measured more precisely, which reduces the uncertainty of measured flame burning velocity, e.g., from ±1.5 cm/s (TC-introduced uncertainty) to ±0.25 cm/s (LIP-introduced uncertainty) in a Φ=0.7 methane/air flame. Development was also achieved by extending the technique of photofragmentation LIF (PF-LIF) of H2O2 in an HCCI engine. Quantitative concentration as well as single-shot imaging of H2O2 were acquired. A similar technique like PF-LIF was also carried out for C2H2 measurements under atmospheric pressure.