INVESTIGATION OF FLAME-FRONT INSTABILITY MECHANISM BY PREFERENTIAL DIFFUSION EFFECT FOR TURBULENT COMBUSTION AT ELEVATED PRESSURE

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This study was carried out comprehension of turbulent combustion and its local combustion characteristics experimentally for more various mixtures and elevated-pressure conditions. Their characteristics were also examined by the concept of the sensitivity of flame stretch or curvature on the burning velocity as well as the preferential diffusion effect, in order to investigate the mechanism of flame-front instabilities on turbulent flames. Additionally, an attempt was made to establish a general-purpose model of turbulent burning velocity. The main conclusions are as follows.・ In order to investigate the local burning velocity characteristics of the turbulent flame of hydrogen added methane or propane mixtures, the local flame displacement velocity S_F was measured directly with using two-dimensional sequential tomograms. S_F plays clearly an important role in the turbulent burning velocity. The burning velocity of turbulent flames S_<Lt> estimated by using the Markstein number attempted to be estimated. A quantitative relationship between S_F and S_<Lt> can be observed only for rich hydrogen or methane and lean propane mixtures.・ Turbulent burning velocity and local burning velocity characteristics for various hydrogen mixtures were examined experimentally. The mean local burning velocities S_L, estimated by taking account of preferential diffusion effect, were estimated. Quantitative accuracy of the proposed simple model for hydrogen mixtures can be clearly more improved by using S_L taking account of u'/S_<L0> as well as φ.・ Finally, effects of the initial pressure on local burning velocities and local flame configurations were examined. There is a possibility that the increase in the initial pressure does not increase the local burning velocity but increase the flame-surface area of turbulent flames.