Laser Raman scattering measurements of differential molecular diffusion in turbulent nonpremixed jet flames of H2CO2 fuel

In this paper the authors 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 H[sub 2]/CO[sub 2] 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 H[sub 2] and CO[sub 2] produces differences between the hydrogen element mixture fraction (f[sub H]) and the carbon element mixture reaction (f[sub C]). The greatest effects occur on the rich side of stoichiometric, where f[sub H] is observed to be smaller than f[sub C] at all Reynolds numbers. Differential diffusion between H[sub 2] and H[sub 2]O creates a net flux of hydrogen element toward the stoichiometric contour and causes a local maximum in f[sub H] that occurs near the stoichiometric condition. A differential diffusion variable z[sub H] is defined at the difference between f[sub H] and f[sub C]. The variance of z[sub H] conditional on f[sub C] also shows that differential diffusion effects are greatest on the rich side of the flame. Conditional variances of z[sub H] are largestmore » at intermediate Reynolds numbers.« less