Simultaneous Raman and Rayleigh measurements of temperature in a premixed methane-air flame at kilohertz sampling rates

Abstract

A data analysis technique has been developed for reducing two-channel, spontaneous rotational Raman measurements of temperature taken at high sampling rates using a cw laser. The temperature is computed from the ratio of the Raman signals in the two channels. This measurement scheme is especially valuable because it is virtually immune to laser beam steering effects and the presence of LDA seed. This makes it possible to carry out simultaneous temperature and velocity measurements at high data rates. The analysis technique utilizes the fact that the only pairs of data which represent possible valid temperature measurements are those for which the observed counts in the two channels are consistent with the temperature calculated from the ratio. This selection process effectively identifies those pairs of data in which the two signals are correlated to some specified degree. Simultaneous Raman and Rayleigh studies were carried out to provide a reasonable comparison of this “correlated” Raman technique to an accepted high-sampling-rate technique. Temperature pdf’s along the flow axis as well as joint pdf’s of simultaneous temperature and velocity measurements are presented which illustrate the utility of this Raman technique.A data analysis technique has been developed for reducing two-channel, spontaneous rotational Raman measurements of temperature taken at high sampling rates using a cw laser. The temperature is computed from the ratio of the Raman signals in the two channels. This measurement scheme is especially valuable because it is virtually immune to laser beam steering effects and the presence of LDA seed. This makes it possible to carry out simultaneous temperature and velocity measurements at high data rates. The analysis technique utilizes the fact that the only pairs of data which represent possible valid temperature measurements are those for which the observed counts in the two channels are consistent with the temperature calculated from the ratio. This selection process effectively identifies those pairs of data in which the two signals are correlated to some specified degree. Simultaneous Raman and Rayleigh studies were carried out to provide a reasonable comparison of this “correlated” Raman technique to an...