Improvement of rotational CARS thermometry in fuel‐rich hydrocarbon flames by inclusion of N₂‐H₂ Raman line widths

Abstract

Abstract In rotational coherent anti‐Stokes Raman spectroscopy (CARS) thermometry applied to air‐fed flames, the temperature sensitivity mainly depends on the intensity distribution of the nitrogen spectral lines. Temperatures are estimated by numerical fitting of theoretical spectra to experimental ones, and one uncertainty in the calculation of theoretical CARS spectra for specific flame conditions is the accuracy in utilized line‐broadening coefficients. In a previous article, self‐broadened N 2 ‐N 2 line widths were considered in the spectral calculations as well as those of N 2 ‐CO, N 2 ‐CO 2 , N 2 ‐H 2 O, and N 2 ‐O 2 . In the present article, we also include N 2 ‐H 2 line widths calculated from a newly developed model, and it is shown that the evaluated temperature from flame spectra increases with increasing mole fractions of hydrogen. For example, in a very rich flame at Φ = 2.5, the use of available line‐width data for all major species gives a temperature raise of 72 K at a temperature of ∼1700 K, in comparison with using self‐broadened N 2 ‐N 2 line widths only. Half of this temperature raise is related to the inclusion of N 2 ‐H 2 line widths. This article emphasizes the importance of using adequate line‐broadening models for rotational CARS thermometry in flames. Copyright © 2009 John Wiley & Sons, Ltd.