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This study focuses on the thermal-diffusive oscillations of the full spectrum of co-flow laminar flames-from premixed to non-premixed through partially premixed flames for Lewis numbers sufficiently greater than unity. A premixedness parameter is identified using the analytical solution to the mixing field downstream of a splitter plate. Different premixedness levels ranging from zero (fully non-premixed) to unity (fully premixed) are then used as Dirichlet data for inlet concentrations of the reactants to the flame. The initial value problem is numerically solved by adopting a thermo-diffusive model and single-step finite rate chemical reaction and using higher-order compact schemes. A thumb-shaped region in the Damk�hler number - premixedness parameter space is identified as corresponding to limit cycle oscillations of the flame. This fills the gap between what is reported for the pulsating instability of non-premixed edge flames recently and fully premixed flames earlier. The thumb-shaped region enlarges with increase in the Lewis number in the range of 1.5-1.7, with marked increase in the oscillatory amplitude of the total heat release. A subcritical Hopf bifurcation is seen to occur at the boundary of this region in the above parametric space. The mechanism of oscillations is studied: hysteresis is found between the upstream and downstream propagation of the flame due to the thermal-diffusive imbalance. The oscillations are plotted in the phase space of the domain-integrated mass and heat diffusive fluxes of and to the reactants. The area of the limit cycle peaks at a particular Damk�hler number and premixedness parameter and drops to zero on both sides in this parametric space. � 2012 The Combustion Institute.

This paper reports the production of nanoaluminum particles using the wire explosion process at our laboratory. Electrical energy is applied to the aluminum wire in an argon atmosphere to yield spherical particles around 50 nm in size. The material is also characterized by a number of methods. The nano-Al is included in bimodal ammonium Perchlorate composite solid propellants, and their burning rates are compared with those containing normal micron- sized aluminum and nonaluminized propellants in a total of 21 formulations in the 1-12 MPa pressure range. Nanoaluminized propellants show ?100% increase in burning rate relative to nonaluminized or microaluminized ones, but only when large-sized coarse ammonium Perchlorate particles are used. Burning-rate plateaus observed in non- and microaluminized propellants are washed out with the addition of nano-Al, but the burning rates of nanoaluminized propellants register low pressure exponents in the elevated pressure range. The results suggest that the heat feedback from the diffusion-limited combustion of nano-Al particles near the propellant burning surface controls the propellant burning rate when sufficiently large parts of the burning surface are made up of the nanoaluminized fine ammonium-perchlorate/binder matrix.