title: Experimental Investigations of Solid Fuel Combustion with Multi-dimensional and Multi-parameter Laser Diagnostics
Creators: name: Li, Tao
Publisher: name: UNSPECIFIED
Year: 2021

description: In the 21st century, climate change is one of the main challenges for the sustainable development of human society and global economics. With worldwide increasing primary energy consumption, reduction of greenhouse gas emissions is pursued by most countries to limit the global warming. Oxy-fuel combustion, among other carbon capture and storage technologies, is a promising technical solution for CO2 reduction with retrofitting of the existing fossil-fuel-fired power plants for future power supply. For industry-scale employment of oxy-fuel combustion technology, a thorough understanding of the flame characteristics of solid fuel particles is desired, requiring fundamental investigations in laboratory experiments. In this work, solid fuel combustion in laminar flows is comprehensively investigated in generic experiments by using advanced non-intrusive measurement techniques. The investigations emphasize ignition and the early-stage volatile combustion of fuel particles, which play an essential role in flame stabilization and propagation for industrial boilers. Oxy-fuel combustion is a complex multi-phase phenomenon with numerous interactive sub-processes involved, demanding in-situ data acquisition of multiple essential scalars and vectors. Thus, this thesis presents the efforts that are made (1) to develop methodology aiming for performing multi-parameter volumetric optical measurements in combustion research, and (2) to study the ignition and flame behavior of high-volatile bituminous coal particles by applying the developed laser diagnostics and further to deepen the fundamental understanding of solid fuel combustion. This thesis is structured in a cumulative dissertation framework, in which six peer-reviewed publications are accommodated in two major parts. Part one underlines the methodological development of high-speed volumetric laser measurements by introducing three major contributions. In a single-shot 3D measurement (paper I), the reaction zone of laminar and turbulent flames is visualized by using volumetric laser illumination. It extends to a quasi-4D flame laser-induced fluorescence (LIF) imaging measurement by combining a 100 kHz pulse-burst laser with a rapid acousto-optic deflector (paper II). By performing tomographic particle image velocimetry (Tomo-PIV) measurements, laser scanning and volumetric illumination methods are simultaneously utilized to analyze the flame-flow interactions of a turbulent flame (paper III). These experimental studies demonstrate the novelty and capability of multi-parameter, volumetric imaging techniques applicable to study solid fuel combustion. In part two, the above-mentioned optical diagnostics are applied in laminar flow reactor experiments with emphasis on a fundamental understanding of ignition and volatile combustion of solid fuel in oxy-fuel conditions. Following a step-wise increase in complexity, single-particle ignition and flame evolution are comprehensively investigated using 2D, multi-parameter diagnostics (paper IV), which simultaneously address geometric properties, e.g., particle size and shape, and reaction relevant quantities, e.g., OH species and flame luminescence. Extending to 3D (paper V), the topology of single-particle volatile flame and its temporal and spatial revolution are explored by the laser scanning OH-LIF. A fundamental understanding of single-particle volatile flame is obtained by evaluating the spherical volatile flame's stand-off distance. Finally, ignition and stabilization of a volatile flame seeded with particle groups are investigated (paper VI). Multi-parameter and multi-dimensional measurements contribute to interpreting particle-particle and particle-flame interactions and their importance in solid fuel combustion. Overall, significant progress is achieved in both methodology development and phenomena analysis. Acquired data provide a solid basement for validation of advanced numerical simulations.