Experimental determination of the flow field velocity and strain rate in a laminar opposed flow H₂/air diffusion flame, via laser doppler anemometry

Abstract

An experimental investigation of an opposed flow hydrogen-air diffusion flame was conducted. The purpose was to experimentally determine the flow field velocity and corresponding strain rate under different operating flow conditions. An axisymmetric opposed jet burner was employed in this experiment where air was supplied to one circular tube, while fuel and diluent were supplied to the opposing circular tube. Velocity measurements were made under two different operating flow rates, via the laser Doppler anemometer. The experimental results are used to assess current counterflow diffusion flame modeling approximations.

The data shows that the radial velocity is approximately linear with radial coordinate, as assumed by most modelings. The boundary conditions (uniform axial velocity, and linear radial velocity) assumed by the potential flow model are appropriate at a particular location upstream of the boundary layer region; and the supply air strain rate approximates the potential flow strain rate, going into the flame boundary layer region. Qualitatively, the plug flow model is a better approximation to the velocity distribution for both flow cases.