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Flow, Turbulence and Combustion

, Volume 98, Issue 4, pp 1153–1172

First Online: 15 February 2017Received: 30 August 2016Accepted: 11 January 2017DOI: 10.1007-s10494-017-9801-6

Cite this article as: Lipatnikov, A.N., Li, W.Y., Jiang, L.J. et al. Flow Turbulence Combust 2017 98: 1153. doi:10.1007-s10494-017-9801-6

Abstract

In order to experimentally study whether or not the density ratio σ substantially affects flame displacement speed at low and moderate turbulent intensities, two stoichiometric methane-oxygen-nitrogen mixtures characterized by the same laminar flame speed SL = 0.36 m-s, but substantially different σ were designed using i preheating from Tu = 298 to 423 K in order to increase SL, but to decrease σ, and ii dilution with nitrogen in order to further decrease σ and to reduce SL back to the initial value. As a result, the density ratio was reduced from 7.52 to 4.95. In both reference and preheated-diluted cases, direct images of statistically spherical laminar and turbulent flames that expanded after spark ignition in the center of a large 3D cruciform burner were recorded and processed in order to evaluate the mean flame radius \\bar {R} {f}\left t ight \ and flame displacement speed \S {t}=\sigma ^{-1}{d\bar {R} {f}} \left - ight . {dt}\ with respect to unburned gas. The use of two counter-rotating fans and perforated plates for near-isotropic turbulence generation allowed us to vary the rms turbulent velocity \u^{\prime }\ by changing the fan frequency. In this study, \u^{\prime }\ was varied from 0.14 to 1.39 m-s. For each set of initial conditions two different mixture compositions, two different temperatures Tu, and six different \u^{\prime }\, five respectively, three statistically equivalent runs were performed in turbulent respectively, laminar environment. The obtained experimental data do not show any significant effect of the density ratio on St. Moreover, the flame displacement speeds measured at u′-SL = 0.4 are close to the laminar flame speeds in all investigated cases. These results imply, in particular, a minor effect of the density ratio on flame displacement speed in spark ignition engines and support simulations of the engine combustion using models that i do not allow for effects of the density ratio on St and ii have been validated against experimental data obtained under the room conditions, i.e. at higher σ.

KeywordsTurbulent flame speed Density ratio Expanding spherical flame Thermal expansion Low Turbulent Intensity Darrieus-Landau instability Experiment 



Autor: A. N. Lipatnikov - W. Y. Li - L. J. Jiang - S. S. Shy

Fuente: https://link.springer.com/



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