Rotational Temperature Measurement of NO Molecule in a Flame through Laser-Induced Fluorescence Spectrum

Abstract

Rotational temperature of NO molecule in methane/air premixed flame was estimated by a spectral matching method. A tunable narrow band ArF excimer laser was used to excite the D²Σ⁺←X²Π(0, 1) band system of NO. Laser beam was introduced in a flame, and the laser-induced fluorescence was resolved into a spectrum by using a spectrograph. On this spectrum, ε and δ bands of upper vibrational level of v´=0 were analyzed. In order to use a spectral matching method, profiles of ε and δ band spectra were calculated theoretically in detail with reliable molecular constants and exact equations, and they were modulated by an experimental slit function. Since the profile of band spectrum was determined as a function of a rotational temperature, a rotational temperature could be estimated using the temperature where the profile of every band spectrum obtained theoretically is fitted to that of experimentally obtained. Applying a spectral matching method on the ε(0, 3), ε(0, 4) and δ(0, 2) band of NO, it was obtained that the rotational temperature is about 1000K. The obtained rotational temperature is almost agreed with the thermocouple temperature.