Roles of thermal and radical quenching in emissions of wall‐stabilized hydrogen flames

A CFD study of propane/air microflame stability

“…His work was followed by many other groups, whose work confirmed that depending on geometry, composition, and flow rate, hydrocarbon/air flames are typically quenched when confined within spaces with critical dimensions < 1-2 mm [5][6][7][8][9]. The two primary mechanisms for quenching in these systems are thermal and radical quenching [2,10,11]. Increased heat-transfer coefficients are inherent to microscales, because for a fixed Nusselt number, the heat-transfer coefficient scales with the inverse of the length scale.…”

“…The small scales in microburners result in lower combustion temperatures due to enhanced heat-transfer coefficients. Thus, we propose that microburners could possibly reduce the gas-phase production of NO [2]. Finally, microburners can also serve as efficient sources of heat for endothermic reactions, such as steam reforming and ammonia decomposition, in integrated microchemical systems for the production of hydrogen for fuel cell applications [3].…”

The effect of depletion of radicals on freely propagating hydrocarbon flames

“…The main source of uncertainty in such analysis is the sticking coefficient, which takes the values from 0 to 1. It depends on the material of the solid wall and in some models is deliberately overestimated in order to understand the maximum extent of the role of radical quenching [11,12]. Recent experimental observations show that the sticking coefficients for typical surface of micro-flow reactors are relatively small and it was found that the radical interaction with the surface has some influence on the combustion characteristics in the case of hot walls and decreased pressures [15][16][17].…”

“…Thus it is important to consider two processes: radical quenching and heat release [11]. Numerical modelling reveals that radical termination mechanism can affect the properties of the flames, and shift the limits of ignition and extinction in the case of radical species interaction with hot walls [11][12][13][14]. The main source of uncertainty in such analysis is the sticking coefficient, which takes the values from 0 to 1.…”

“…It is known that such processes as Soret diffusion [2][3][4][5][6][7][8], radical-wall interaction [9][10][11][12][13][14][15][16][17], adding of flame inhibitors/flame suppressants [18,19] can affect the concentration of radicals in the In hydrocarbon flames the inclusion of Soret diffusion affects the mass fluxes of light components of reacting mixtures, mainly, H and H 2 [2][3][4][5][6][7]. In freely propagating flames it is sufficient to consider the thermal diffusion of H radicals, which causes the additional flux of H atoms in the downstream direction.…”