Investigation of differential diffusion in turbulent jet flows using planar laser Rayleigh scattering

In 1979, Professor Bilger was among the first faculty to have a sabbatical visit at the new Combustion Research Facility (CRF) at Sandia Laboratories, in Livermore, California. During this sabbatical, Professor Bilger received from Dr. Mike Drake, then at General Electric Corporate Research and Development, an advance copy of the pioneering paper of Raman scattering in a turbulent flame of H2 into air, later published as Drake et al. [1]. Bilger recognized that the laser Raman data were showing the effects of differential diffusion of H2 relative to diffusion of oxygen, nitrogen, and water. In the turbulent jet flame of H2, the effects of differential diffusion were convolved with chemical reaction and heat transfer. A seminal paper emerged [2]. Bilger’s early interest in differential diffusion led to other experimental [3] and computational [4] investigations of the topic as well. In an effort to isolate the effect of differential diffusion without the added complication of chemical reaction with heat release, a nonreacting experiment was proposed at the end of the theoretical paper by Bilger and Dibble [5]. That paper presented a numerical model of a turbulent jet of a binary mixture, into air. The binary mixture, henceforth called “fuel,” consisted of 7 mol% Freon in 93% H2. In the numerical model, a turbulent diffusivity was added to the molecular diffusivity of each species, H2, Freon, and air.