Files and links (1)
PDFOpen Access (License Unspecified), Open Access
Dissertation
Development of absorption-based spectroscopic techniques for detection of diatomic and polyatomic radicals in flames
Doctor of Philosophy (Ph.D.), Drexel University
Jan 1998
DOI:
https://doi.org/10.17918/00000454
Abstract
Absorption-based laser diagnostic techniques have been developed and applied in flame environments to measure diatomic and polyatomic transient species. The in situ detection and quantification of radical species improves our understanding of the complex chemical kinetics existing in many combustion systems and provides a data base to aid in the development and evaluation of chemical kinetic models. This research specifically focused on two techniques: degenerate four-wave mixing (DFWM) and cavity ringdown laser absorption spectroscopy (CRLAS). These two methods can be considered complementary due to different spatial, temporal, and minimum detection sensitivities. The development phase of this research program focused primarily on DFWM and stimulated Raman scattering (SRS). A tilted backward pump DFWM (t-DFWM) geometry has been shown to improve the signal-to-noise ratio by an order-of-magnitude. It was found that a small tilting angle (ca. 0.5 [degrees]) increases the signal strength by a factor of 1.5-2.0 due to the replacement of the signal-collecting beamsplitter with a mirror, and decreases the measured noise intensity by a factor of 4-7. A further increase in tilting angle reduces the signal intensity: thus the optimal t-DFWM geometry is for the smallest angle experimentally possible. The application phase of this research program included the detection of CN via the B-X violet band by t-DFWM (the first such measurement reported) in an atmospheric-pressure flame. The transition saturation conditions were determined and allowed for subsequent DFWM CN thermometry measurements. To determine the feasibility of polyatomic spectroscopy in flames, the DFWM and CRLAS absorption intensities for HCO, CH3, HO2, ~ a1A1 CH2, and C3H3 were calculated based on model-predicted radical concentrations and published absorption cross sections. The results indicated that DFWM lacks the sensitivity to measure these radicals, while CRLAS can be used to measure HCO and CH3 in low pressure CH4/O2/N2 flat flames. The cavity ringdown technique was then successfully implemented to detect HCO via the A-X visible band and CH3 via the mid-infrared [nu]_3 fundamental vibrational band in low pressure CH4/O2/N2 flat flames. The detection of CH3 constitutes the first infrared detection of a polyatomic radical species in a high temperature combustion environment. Mid-infrared spectral congestion in flames was found to be significant, and complicated the identification procedure. Further, the many strongly-absorbing features may prohibit the use of this spectral region for monitoring trace species in reacting systems. The height above burner absorption intensity profiles for HCO and CH3 were then measured, converted to absolute number densities, and compared to applicable chemical kinetic models (both the Miller-Bowman and GRI-2.11 mechanisms). (Abstract shortened by UMI.).
Metrics
67 File views/ downloads
16 Record Views
Details
- Title
- Development of absorption-based spectroscopic techniques for detection of diatomic and polyatomic radicals in flames
- Creators
- Kenneth William Aniolek
- Contributors
- Nicholas Peter Cernansky (Advisor)David Leslie Miller (Advisor) - Drexel University, Mechanical Engineering and Mechanics
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xviii, 232 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Engineering (1970-2026); Mechanical Engineering (and Mechanics) [Historical]; Drexel University
- Other Identifier
- 991014970333204721