Raman–Rayleigh scattering measurements in reacting and non‐reacting dilute two‐phase flows

Simultaneous space‐ and time‐resolved measurements of scalars were made in reacting and non‐reacting dilute, two‐phase, jet flows of methanol. The spontaneous Raman–Rayleigh scattering technique was used to measure temperature and the concentrations of CH₃OH, O₂, N₂, H₂, H₂O, CO and CO₂. In the reacting case, laserinduced fluorescence from the hydroxyl radical was jointly measured. The two‐phase flow is formed at atmospheric pressure at the exit of an axisymmetric jet centered in a co‐flowing stream of air. At the measurement location of ten fuel jet diameters downstream of the nozzle exit plane the volume percentage of liquid in the center of the jet is estimated at about 0.015%. The Rayleigh‐scattered signal can only be used as a marker for the existence of liquid in the measurement volume as it is overhwlemed by Mie and possibly geometrical scattering from droplets. The methanol Raman signal from the liquid–gas mixture increases, mainly owing to the increase in the number density of molecules and the local field effect. Raman signals from other gaseous species are not affected by the existence of droplets in the measurement volume. Gas‐phase temperature is obtained from the sum of the species number densities. The fluorescence from OH shows occasional unrealistic overshoots for rich mixtures, which indicates some interference due to the existence of droplets.