Numerical Analysis on Hydrodynamic Stability of Hydrogen Premixed Flames.

Abstract

The instability of hydrogen premixed plane flames has been studied by numerical analysis. The numerical model includes detailed hydrogen-oxygen combustion with 17 elementary reactions of eight reactive species and a nitrogen diluent, compressibility, viscosity, heat conduction, and molecular diffusion. We calculated the evolution of disturbed plane flames in hydrogen-air mixtures of equivalence ratios 0.75, 1.0, and 1.5. Sufficiently small disturbance of the flames growing exponentially with time was numerically reproduced and growth rates of disturbance depending on the wave numbers were obtained. The unstable region in the case of equivalence ratio 1.5 is narrow compared with that in the other cases, although the burning velocity is larger and the preheat zone thickness is thinner, because the diffusive-thermal effects play an important role on the flame instability. Moreover, it was shown that the spacing between cells in cellular flames is equivalent to the characteristic wavelength (wavelength of disturbance having maximum growth rate). The cell size obtained in the simulation is in qualitative agreement with experimental results.