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Title: Laser-based temperature pressure & species concentration measurements in combusting and non-combusting flows
Author: Luers, Andrew
ISNI:       0000 0004 7232 6608
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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The development of Laser Induced Thermal Grating Spectroscopy (LITGS) and Degenerate Four-Wave Mixing (DFWM) techniques for measurements in combusting and non-combusting flows is presented. The two techniques are used simultaneously with nitric oxide (NO) as an absorbing species. Signals generated by degenerate and non-degenerate probes are studied for NO in N2 buffer gas up to 4 bar, using a pulsed laser system to excite the (0, 0)γ-bands of NO at 226.21 nm. Contributions to the signal from scattering off the coherent or population grating of DFWM are distinguished from the scattering off the thermal grating of LITGS. A systematic study of LITGS in NO is presented as a means of thermometry in air-fed combustion. LITGS signals from combustion-generated NO in a laminar, pre-mixed CH4/O2/N2 flame on an in-house constructed slot burner are used to derive temperature values as a function of O2 concentration and position in the flame at 1 bar and 2.5 bar total pressure. Temperature values, consistent with the calculated adiabatic flame temperature, are derived from averaged LITGS signals over 50-100 single shots at 10 Hz repetition rate in the range of 1600 K - 2400 K with a pressure-dependent uncertainty of ±1.8% at 1 bar to ±1.4% at 2.5 bar. Based on observed signal-to-noise ratios the minimum detectable concentration of NO in the flame is estimated to be 80 ppm for a 5 second measurement time at 10 Hz repetition rate. LITGS signal shape is used to simultaneously derive pressure and temperature. Pressures are found to match measured gauge pressure well at ambient conditions along the full range of pressures measured from 1 to 5 bar and an extension of the technique is discussed for use in a high pressure combustion environment.
Supervisor: Gregori, Gianluca Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
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