Kazumi Iwai

Flame propagation through mixtures with concentration gradient

The effect of the concentration gradient on the characterstics of flame propagation when the direction of flame propagation is normal to that of the concentration gradient was studied. The velocity of flame propagation through a mixture with a known concentration distribution established over methanol or ethanol was measured by using high-speed schlieren photography. The concentration distributions in the combustion chamber were predicted theoretically and confirmed using gas chromatagraphy. The shape of a propagating flame appeared to depend on the concentration distribution before ignition. The leading flame front usually propagated through a layer where the mixture composition before ignition was closer to that for the maximum flame velocity in a homogeneous mixture. The propagation velocity of the leading flame front was found to decrease as the difference between the mixture composition of the layer along which the leading flame front propagated and the composition for maximum flame velocity in a homogeneous mixture increased, or as the absolute value of the concentration gradient at the layer increased. The experimental results indicate that the product of the height of the combustion chamber and the absolute value of the concentration gradient is an important parameter for characterizing flame propagation through a mixture with concentration gradient. The propagation velocity of the leading flame front decreased as the value of this parameter increased.