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Abstract: Important role of chemical interaction in flame extinction is numerically investigated in downstream interaction among lean (rich) and lean (rich) premixed as well as partially premixed H2- and CO-air flames. The strain rate varies from 30 to 5917 s−1 until interacting flames cannot be sustained anymore. Flame stability diagrams mapping lower and upper limit fuel concentrations for flame extinction as a function of strain rate are presented. Highly stretched interacting flames are survived only within two islands in the flame stability map where partially premixed mixture consists of rich H2-air flame, extremely lean CO-air flame, and a diffusion flame. Further increase in strain rate finally converges to two points. It is found that hydrogen penetrated from H2-air flame (even at lean flame condition) participates in CO oxidation vigorously due to the high diffusivity such that it modifies the slow main reaction route CO + O2 → CO2 + O into the fast cyclic reaction route involving CO + OH → CO2 + H. These chemical interactions force even rich extinction boundaries with deficient reactant Lewis numbers larger than unity to be slanted at high strain rate. Appreciable amount of hydrogen in the side of lean H2-air flame also oxidizes the CO penetrated from CO-air flame, and this reduces flame speed of the H2-air flame, leading to flame extinction. At extremely high strain rates, interacting flames are survived only by a partially premixed flame such that it consists of a very rich H2-air flame, an extremely lean CO-air flame, and a diffusion flame. In such a situation, both the weaker H2- and CO-air flames are parasite on the stronger diffusion flame such that it can lead to flame extinction in the situation of weakening the stronger diffusion flame. Important role of chemical interaction in flame extinction is discussed in detail. [Copyright &y& Elsevier]

Abstract: Numerical study is conducted to understand the impact of fuel composition and flame radiation in flame structure and their oxidation process in H2/CO synthetic gas diffusion flame with and without CO2 dilution. The models of Sun et al. and David et al., which have been well known to be best-fitted for H2/CO synthetic mixture flames, are evaluated for H2/CO synthetic mixture flames diluted with CO2. Effects of radiative heat loss to flame characteristics are also examined in terms of syngas mixture composition. Importantly contributing reaction steps to heat release rate are compared for the synthetic gas mixture flames of high contents of H2 and CO, individually, with and without CO2 dilution. The modification of the oxidation pathways is also addressed. [Copyright &y& Elsevier]