Laser Raman scattering measurements of differential molecular diffusion in turbulent nonpremixed jet flames of H2/CO2 fuel

In this paper we explore the effects of differential diffusion in nonpremixed turbulent jet flames. Pulsed Raman scattering spectroscopy is used to measure temperature and species concentrations in chemically reacting jets of H2/CO2 into air, over a range of jet Reynolds numbers from 1,000 to 30,000 based on cold jet fluid properties. Results show significant effects of differential diffusion at all jet Reynolds numbers considered. Differential diffusion between H2 and CO2 produces differences between the hydrogen element mixture fraction (ξH) and the carbon element mixture fraction (ξC). The greatest effects occur on the rich side of stoichiometric, where ξH is observed to be smaller than ξC at all Reynolds numbers. Differential diffusion between H2 and H2O creates a net flux of hydrogen element toward the stoichiometric contour and causes a local maximum in ξH that occurs near the stoichiometric condition. A differential diffusion variable zH is defined as the difference between ξH and ξC. The variance of zH conditional on ξC also shows that differential diffusion effects are greatest on the rich side of the flame. Conditional variances of zH are largest at intermediate Reynolds numbers.