Experimental study on flame instabilities of laminar premixed CH4/H2/air non-adiabatic flat flames

Abstract

The intrinsic instability of laminar flame is one of the classic subjects in flame dynamics, which presents the dynamic response of laminar premixed flamelets to weak perturbations. The instabilities of laminar premixed CH4/H2/air flames stabilized on a non-adiabatic McKenna burner were investigated. The quantitative parameters of flame front were measured by OH-PLIF (Planar Laser Induced Fluorescence) technique. Combining theoretical analysis, a non-adiabatic linear dispersion relationship was derived by introducing the effect of heat loss and buoyance. The controlling factors on the cellular scale were further investigated. Heat loss was found to be the dominant factor in determining the cellular scale. High rate of heat loss can result in small cellular scale. On the other hand, the properties of mixtures, Lewis number Le and Markstein number Ma, also played an important role. If Le is more away from unit (Le<1), the thermal-diffusive instability can be enhanced and the cells tend to exhibit a large scale. While with a larger (smaller) Ma, the stretch-induced counteract effect is stronger (weaker), which results in a less (more) irregular flame front and minor (larger) cellular scale. These three main factors were coupled to determine the final structure of cellular flame.