Suppression of cellular structure in slot-burner flames

The mechanisms responsible for suppression of corrugated (cellular) structure in premixed flames have been investigated for slot-burner flames. Employing a novel variable-width slot burner, the effects of rim temperature, aerodynamics at the rim, and slot width were isolated. The results reveal that the dominant mechanism responsible for suppression of corrugated structure with increasing flow rate or decreasing slot width is time along the flame front. The results also suggest that stretch-induced stability due to positive strain rate and curvature at the base of rim-stabilized flames is essential for suppression of corrugated structure. Additionally, the suppression process, previously thought to be abrupt, was identified to occur over a distinct range of velocities, and this range was found to increase with increasing slot width. This new regime, defined as the transition regime, was characterized by a smooth, two-dimensional structure in the lower region near the rim and a corrugated, multi-dimensional structure in the upper region near the tip. A critical slot width, defined as w_c, was also identified beyond which the corrugated structure could not be suppressed throughout the entire flame with increasing velocity. By examining the time available for growth of the instability, a simple model was developed that qualitatively describes the experimental results. For the 1-butene/air/CO₂ mixture analyzed, particle-tracking measurements yielded a characteristic time for growth of 22 ms and a critical slot width of w_c = 0.7 cm, which agrees well with the model prediction of w_c = 0.75 cm.