Simultaneous Imaging of Temperature and OH Number Density in Turbulent Diffusion Flames

Abstract

A single laser source and a single intensified CCD camera have been used to image temperature and the hydroxyl radical, OH in turbulent nonpremixed flames. Images are simultaneous and quantitative. Temperature is derived from Rayleigh scattering. Laser Induced Fluorescence (LlF) is used to image OH. Correction of the LIF image for quenching effects is done using a combination of laminar flame calculations and the temperature measurements. Images for flames of the following fuels are presented: CH₃OH, C₂H₅OH, CNG (91% CH₄ by volume) and CNG-H₂(31% CNG, 69% H₂ by volume). The OH profile is used as a measure of reaction zone thickness. Number densities of OH are found to be in superflamelet levels for all flames investigated here. Temperatures agree well with laminar flame computations. Flames show evidence of partial or full premixing of the fluid in the reignition zone at high velocities downstream of regions of high local extinction. The OH profiles are seen to increase in width and this is consistant with an increase in calculated reaction zone width and an increase in stoichiometric mixture fraction. An increase in Reynolds number alone does not change the OH profile thickness.

Keywords:

• Laser imaging
• temperature
• OH
• Rayleigh
• turbulent diffusion flames