Application of Resonant and Non-Resonant Laser-Induced Plasmas for Quantitative Fuel-to-Air Ratio and Gas-Phase Temperature Measurements

In this work, two laser-induced plasma techniques are used for gas-phase chemical and temperature measurements. The first technique, laser-induced breakdown spectroscopy (LIBS) is applied for fuel-to-air ratio (FAR) measurements in a well calibrated Hencken flame. In Chapter I, relevant technical and background information for each technique is provided. In Chapter II, measurements are first performed for high-pressure (1-11 Bar) methane-air flames, for which calibration curves are generated using the emission ratio of hydrogen at 656 nm and ionic nitrogen at 568 nm. The effect of pressure on the sensitivity and precision of the resulting calibrated curves is evaluated. Results indicate a degradation of measurement precision as environmental pressure increases, with data indicating that fluctuations of the plasma play a major part in this behavior. Expanding upon this work with LIBS, a comparison of FAR calibration curve results for atmospheric methane-air Hencken flame using three different laser pulse widths, femto-, pico-, and nanosecond regimes, is done in Chapter III. The results are discussed in the context of potential advantages for high-pressure LIBS-based FAR measurements. Results indicate that while nanosecond duration pulses provide better precision at 1 Bar conditions, femtosecond duration pulses might be better suited for high-pressure measurements.In Chapter IV, the radar REMPI technique, which uses microwave scattering from a plasma created by selective multiphoton ionization of molecular oxygen, is used for gas-phase temperature measurements through the wall of ceramic-enclosed environments. Specifically, measurements are done through the wall of a heated laboratory flow reactor and through the wall of a ceramic well-stirred reactor. Results show good agreement with thermocouple and/or computational modeling and the effectiveness of radar REMPI for through-the-wall measurements.In Chapter V, a new technique is discussed, namely acoustic REMPI, which utilizes the pressure wave generated from the creation of the REMPI plasma for diagnostics. The acoustic emission from the plasma is characterized and used for gas-phase temperature measurements. Comparison, with radar REMPI shows a high-level of agreement.Finally, in Chapter VI, a summary of the work in this dissertation is provided along with a discussion of potential for work in the future.