Temporally Resolved Two-Dimensional Spectroscopic Study on the Effect of Highly Preheated and Low Oxygen Concentration Air on Combustion

Spontaneous emission spectroscopy has been applied to measure the time-resolved temperature profiles of gaseous fuel flames using high temperature and low oxygen concentration combustion air. Two emission peaks of C2 radical species have been observed at visible wavelengths from propane-air flames. The ratio of these two peaks depends on the flame temperature. The relationship between the ratios of these peaks was correlated with the thermocouple output using a premixed flat flame burner and a multichannel CCD spectrometer. Using this relationship, the flame temperature was determined from the ratio of the C2 peaks. Time-resolved emission intensity profiles of the two C2 bands (two-wavelength image) were observed simultaneously with a high sensitivity video camera fitted with an optical system. The time-resolved temperature profiles were constructed from these intensity profiles by utilizing the previously determined relationship at each pixel. To evaluate fluctuations of flame temperatures, the standard deviation profiles for the temperature profiles have been constructed. This spectroscopic diagnostic technique has been used to measure the profiles of mean flame temperature and temperature fluctuation produced from a concentric diffusion flame using propane as the fuel and high temperature and low oxygen concentration combustion air. In this study, the effect of air-preheat and low oxygen concentration in the combustion air on the subsequent flame temperature and temperature fluctuations has been determined by analyzing the spectra of spontaneous emission from the C2 radicals.