| Summary: | <p> Combustion is widely used for materials processing, propulsion, and power production. Understanding the temporal and spatial variations within practical combustion systems can help to optimize their stability, uniformity, emissions, and/or efficiency. Wavelength modulation spectroscopy (WMS) provides quantitative, non-intrusive, time-resolved measurements of line-of-sight thermodynamic properties in a gas sample. This dissertation describes the development and application of novel WMS sensors for measurements in industrial flame environments. After an overview of WMS, we describe the development of the first WMS sensor to measure OH radical near 1491 nm. We perform the first dual-comb spectroscopy measurement above a premixed flame in order to develop accurate models for the H<sub>2</sub>O absorption that interferes with OH absorption at elevated temperatures. The model improves the absolute OH measurement accuracy. We apply the OH sensor in conjunction with temperature and H<sub>2</sub>O mole fraction WMS sensors to characterize a premixed ribbon burner interacting with an industrial chilled-roller polymer-treatment system. Measurements at the surface of the polymer, together with post analysis of the surface oxidation, provides the first experimental demonstration of the connection between concentrations of OH radical in a premixed flame and the level of oxidation of polypropylene film in flame processing. The WMS sensors are used to probe the temporal, vertical and 2D variation in the heated, buoyant jet above an iron-chromium alloy catalytic combustor, which could be used for industrial materials processing. We develop a new pathlength correction method that uses computational fluid dynamics simulations to account for the effect of the narrowing and billowing of the heated gases on the measured water vapor mole fraction. The vertical profiles of temperature and H<sub>2</sub>O mole fraction show a high likelihood of additional combustion above the catalytic surface under certain operating conditions. Finally, we extend the WMS technique to measure high-density gases by performing the first large amplitude wavelength modulation spectroscopy with a MEMS-Tunable Vertical Cavity Surface-Emitting Laser (MEMS-VCSEL). We demonstrate the technique on high-pressure mixtures of CO<sub>2</sub> in air that are 2.5 times higher density than previously published WMS measurements (equivalent to greater than 255 atm at 1500 K). Together, these measurements demonstrate the utility of WMS sensors in optimizing and characterizing industrial combustion systems.</p><p>
|
|---|
