Flame Behavior in Micro channels with Narrowing
Understanding of features of dynamical behavior of flame front in micro channels is necessary for developing of new gas burning technologies, such as burning of lean mixtures in porous media or micro combustion. It is necessary to create adequate models of flame propagation in channels with variable cross sections, nonhomogeneous temperature in walls and nonhomogeneous gas flow to develop small-size energy-transducing devices. It is well-known that flame can only propagate in channels with transverse diameter more than critical diameter. Critical diameter is usually considered as minimal diameter of indefinite channel where the flame propagation is possible. Critical diameter is usually considered as minimal diameter of indefinite channel where flame propagation is possible. Not only transverse size of a channel influences on flame propagation in micro devices, but its geometry and flow speed as well. The problem about flame propagation in the flow of inflammable mixture is solved in the present study. It is assumed that flame can freely propagate far from narrowing zone because diameter of the channel is more that critical diameter there. Diameter of narrowing zone is less than critical diameter. Data about gas flow velocity, length and diameter of narrowing, which influence on flame propagation limit, are gotten. It is shown that flame can pass through the narrowing even if transverse size is less than critical one, because time of heat exchange between chemical reaction zone and channel walls is limited and depends on the gas flow velocity. Critical diameter of narrowing depending on flow velocity and longitudinal size was constructed. Calculations are made in the frame of two-dimensional model with one-step chemical kinetics, which take into account structure of viscous flow and heat exchange between gas and channel walls.