title: Flame-Wall Interactions at Elevated Pressure Studied with Advanced Laser Diagnostics
Creators: name: Johe, Pascal
Publisher: name: UNSPECIFIED
Year: 2024

description: Despite the ongoing progress in electrification driven by the indispensable substitution of fossil fuels with renewable energy sources, the thermochemical conversion of chemical energy carriers is expected to continue playing an important role in the energy transition. This underlines the necessity for continual development of low-emission combustion technologies, grounded in a comprehensive understanding of the underlying physical processes through ongoing fundamental research efforts. Within this cumulative dissertation, the complex phenomenon of flame-wall interaction (FWI), which is an essential aspect of practical combustion systems, is investigated experimentally using advanced laser diagnostics. FWI involves the mutual interaction between chemical reaction, solid surface and fluid flow and is associated with undesired effects, such as reduced efficiency and increased pollutant emissions. The main objective of this thesis, which includes three peer-reviewed publications, is the investigation of fundamental aspects of FWI at elevated pressures and increased Reynolds numbers, mimicking operating conditions of practical combustion systems.
Experiments are carried out within a novel, enclosed test rig - the pressurized side-wall quenching (SWQ) burner - which provides a reproducible, generic configuration of a premixed flame interacting with a cold, solid wall. This test rig was designed, built and commissioned within the scope of this thesis and is presented in detail. The process under investigation is examined at operating pressures ranging between atmospheric and 5 bar absolute and Reynolds numbers up to 20,000 using various laser diagnostics. Limitations of such measurement techniques resulting from the complex test rig design and process-inherent challenges arising with increasing pressure are reported.
First, a characterization of the turbulent flow field and the combustion dynamics is conducted using velocity data and spatial fields of the instantaneous flame front positions, provided by high-speed and low-speed particle image velocimetry measurements and planar, laser-induced fluorescence of the hydroxyl radical (OH-PLIF). This involves the inspection of the inflow and the near-wall flow field under non-reacting and reacting conditions, as well as the examination of the transient flame front motion. Building on this, turbulent flame propagation close to the wall is further analyzed in terms of the flame surface density (FSD), a central quantity in numerical combustion modeling, which is derived from measured flame front positions (OH-PLIF) following two common approaches. Furthermore, the near-wall thermochemistry of the turbulent flame quenching process is explored through simultaneous measurements of the gas-phase temperature and mole fractions of CO2 and CO by means of dual-pump coherent anti-Stokes Raman spectroscopy and laser-induced fluorescence of CO. These measurements represent the first reported attempt to investigate the thermochemistry of FWI at pressures above atmospheric by means of multi-parameter laser diagnostics.
This cumulative dissertation presents novel insights into the impact of elevated pressure and increased Reynolds numbers on turbulent FWI and provides experimental data for model validation. It furthermore, contributes to the FWI research community by exploring the limits of state-of-the-art laser diagnostics for measurements in pressurized, near-wall reactive flows.