• Journal of the Korean Society of Combustion
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• v.18 no.4
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• pp.37-43
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• 2013

The effects of preferential diffusion of hydrogen in interacting counterflow $H_2$-air and CO-air premixed flames were investigated numerically. The global strain rate was varied in the range $30-5917s^{-1}$, where the upper bound of this range corresponds to the flame-stretch limit. Preferential diffusion of hydrogen was studied by comparing flame structures for a mixed average diffusivity with those where the diffusivities of H, $H_2$ and $N_2$ were assumed to be equal. Flame stability diagrams are presented, which show the mapping of the limits of the concentrations of $H_2$ and CO as a function of the strain rate. The main oxidation route for CO is $CO+O_2{\rightarrow}CO_2+O$, which is characterized by relatively slow chemical kinetics; however, a much faster route, namely $CO+OH{\rightarrow}CO_2+H$, can be significant, provided that hydrogen from the $H_2$-air flame is penetrated and then participates in the CO-oxidation. This modifies the flame characteristics in the downstream interaction between the $H_2$-air and CO-air flames, and can cause the interaction characteristics at the rich and lean extinction boundaries not to depend on the Lewis number of the deficient reactant, but rather to depend on chemical interaction between the two flames. Such anomalous behaviors include a partial opening of the upper lean extinction boundary in the interaction between a lean $H_2$-air flame and a lean CO-air flame, as well as the formation of two islands of flame sustainability in a partially premixed configuration with a rich $H_2$-air flame and a lean CO-air flame. At large strain rates, there are two islands where the flame can survive, depending on the nature of the interaction between the two flames. Furthermore, the preferential diffusion of hydrogen extends both the lean and the rich extinction boundaries.

• Economic and Environmental Geology
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• v.39 no.2 s.177
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• pp.151-162
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• 2006

Characteristics and changes of groundwater qualify were investigated in a riverbank filtration area at Daesan-myeon, Changwon City, Korea. The total dissolved solids (TDS) in groundwater samples collected in October were much less than that in March, indicating the mixing with recharged water from precipitation, as well as the changes of dissolved oxygen profiles at monitoring wells from March to October. Redox processes at depths appeared to trigger Fe and Mn contamination of groundwater in riverbank deposits. Amorphous oxyhydroxides md carbonate minerals such as $MnCO_3$ were probably the reactive phases for dissolved Fe and Mn, respectively. Groundwater contamination by nitrate-nitrogen $(NO_3-N)$ was controlled by the redox processes and subsequent denitrification at the sampled depths. Distribution of $NO_3-N$ concentrations at monitoring wells suggested that the nitrate contaminants were originated from agricultural facilities on the riverbank deposits. Some of monitoring wells, DS-2, D-2, DS-3, SJ-1, and SJ-3, were only partially penetrated into the sand/gravel aquifer, and subsequently, could not fully function to detect the water quality changes for the pumping wells. Proper measures, with regulating agricultural activities in the riverbank deposits, should be carried out to prevent groundwater contamination of the riverbank filtration area.