Cavity Enhanced Magneto Optic Rotation for Measurement of HO[2

Abstract

The goal of reduced emissions and increased efficiency in transportation has required investigation into advanced engine designs. Some of these advanced engines use charge reactivity to closely control the engine ignition and combustion process and thus the overall engine operation. Reactivity controlled operation requires models of the chemical kinetics at the low end of operating temperatures. The current models are lacking detail in the low and intermediate temperature region where hydroxyl (OH), hydroperoxy (HO2), and alkylperoxy (RO2) radicals play an important role in the oxidation chemistry. Measurement of these radicals is made difficult in combustion systems because of the strongly absorbing stable products of combustion, such as CO2 and H2O, which obscure the absorption features of HO2 and RO2. Therefore, there is a need for sensitive and selective diagnostics which can quantitatively measure these weakly absorbing small peroxy radicals in combustion systems. This work advances the development and application of a sensitive and selective laser diagnostic technique called Cavity Enhanced Magneto-Optic Rotation (CEMOR) for quantitative measurement of paramagnetic species, specifically HO2 radicals. CEMOR combines the sensitivity of cavity ringdown spectroscopy (CRDS) and the selectivity of magneto-optic rotation (MOR) spectroscopy. This work presents a novel design of CEMOR with a continuous wave laser source for measurement of HO2. The narrower bandwidth of continuous wave lasers offers increased spectroscopic resolution over the pulsed Nd:YAG/OPO laser used for previous CEMOR development. Continuous wave cavity ringdown spectroscopy (cw-CRDS) is integrated with MOR in order to make high resolution scans of HO2 in a flash photolysis cell. Modeling results of the magnetic field strength in studies of MOR and CEMOR with a slot burner using permanent magnets, and of CEMOR in a flash photolysis cell using a solenoid are presented. Magnetic field strength effect is shown to have a linear relationship with MOR signal and a mechanism for measurement of its effect on CEMOR signal is described. The objective of this dissertation is to demonstrate that CEMOR can be used to make measurements of HO2 by increasing its resolution through the incorporation of a continuous wave distributed feedback (DFB) diode laser. The intellectual merit of this work is found in the design of a novel laser spectroscopy technique which is capable of sensitive and selective detection of paramagnetic species. This initial work did not demonstrate successful application of continuous wave CEMOR to measurement of HO2, yet it provides a path forward for this goal in a flash photolysis cell and cool flame burner. The present work also provides a method which can easily be adapted to measurement of alkyl peroxy (RO2) radicals.%%%%Ph.D., Mechanical Engineering and Mechanics – Drexel University, 2016