Analysis of Barrel-Stratified Lean-Burn Flame Structure by Two-Dimensional Chemiluminescence Measurement

The postflame reaction zone structure of a lean-burn flame was studied by two-dimensional consecutive imaging of flame chemiluminescence using an image intensifier with short-decay phosphor. Quantitative and statistical analyses were performed to elucidate the effect of tumble and charge stratification on the flame behavior. It was found that in the early stage of combustion, significant air entrainment enhancement was realized by tumble but its effect on eddy burning was small. After the completion of flame propagation, however, tumble activated the eddy burning process. Charge stratification activated both air entrainment and eddy burning. These phenomena could be related to the flow field structure after the collapse of tumble. A procedure to derive the tomographic image of the reaction zone was proposed. It was found that under a uniform mixing condition, no reaction-zone structure was observed. When charge was stratified, however, an annular postflame reaction zone was observed behind the flame front.