Development of dual-broadband rotational CARS for applied flame diagnostics
Sammanfattning: The thesis work involved the further development of the dual-broadband rotational coherent anti-Stokes Raman spectroscopy (DB-RCARS) approach to applied flame diagnostics. This included the development of new experimental approaches, of new theoretical rotational CARS models, and of new evaluation routines as well as exploration of the potential of DB-RCARS to provide reliable thermometric measurements and measurements of concentration under a variety of conditions common in combustion research. A polarization approach for rotational CARS was developed, one shown to completely suppress the non-resonant contribution of the CARS signal. Use of it was demonstrated by thermometry on the fuel side of a laminar methane diffusion flame. Use of DB-RCARS, together with a modeless dye laser that was constructed was also demonstrated. It was shown that under ambient conditions the temperature precision was significantly improved. Rotational CARS models for carbon dioxide and acetylene were developed and improved, respectively. This was done in connection with experiments under well defined conditions aimed at validating the use of these models for thermometry and measurements of concentration. Also, simultaneous multi-species detection (of N2, O2, CO2 and CO) and thermometry were demonstrated by means of rotational CARS in a laminar carbon monoxide diffusion flame. A species-specific weighting routine was developed that enhances importance of weak peaks in the spectral fitting algorithm. Use of the routine was found to improve the precision and the accuracy of measurements of concentration. The routine was applied to evaluation of low concentrations of O2 and CO in spectra recorded in laminar premixed hydrocarbon flames. The routine also improved the temperature precision of high temperature measurements. Thermometry was applied to the product gas of laminar premixed hydrocarbon flames. The effects of collisional broadening on the rotational Raman linewidths of nitrogen brought about by the product gas species involved were shown to be important in quantitative thermometry. Use of single-shot thermometry in high-pressure hydrocarbon flames was also demonstrated. A prerequisite for quantitative measurements was the calibration measurements in air, N2 and O2 under high temperature and pressure conditions in a cell.
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