Four Types of Chaotic Dynamics
in Cellular Flames

Experimental Observations of Pulsating-Cellular States

The pulsating-cellular state occurs at parameters near the onset of the cellular instability in both isobutane-air and propane-air flames. Five sequential frames of the pulsating-cellular state are shown in Figure ld. In frame 1 a single central cell is surrounded by seven distinct cells whose boundaries appear distorted into leaf-like shapes due to the radial motion. As the flame front contracts in frames 2 and 3, the bright spots evolve into six wedge-shaped outer cells in the maximum of the next oscillation cycle (frame 5).

The periodic nature of this mode can be seen in the rhythmic nature of the expansions and contractions. The nonperiodic nature of the mode manifests itself by the varying position and the changing number of bright regions that appear on successive expansions. The power spectrum of this mode shows both sharp peaks due to the radial pulsation as well a broad background due to the chaotic motion of the cells .

At larger values of the flow rate a 9/1 ordered state of cellular flames is observed with no pulsations. At lower values of the flow rate, the cellular structure is not present, and the flat flame front pulsates in the radial mode in which it periodically and uniformly changes its radial extent. At still lower values the flame front extinguishes. The occurrence of these states with increasing flow rate is shown in Figure 6 a-c. A steady flame front is not observed at equivalence ratios exhibiting the pulsating-cellular interaction.

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