Flame Quenching/Re-Ignition Behavior

Flame Quenching/Re-Ignition Behavior

Details

Flame quenching/re-ignition behavior, as one of the flame dynamic features, can be further elucidated from the high-speed OH-PLIF images shown in the upper Figure. A sequence of 4 consecutive images with 0.2 ms time interval is shown. The downstream part of RZ is quenched (red circle) with disappearing OH signal. Small isolated pockets (circled in white) of OH show a propagating nature and eventually merge to a larger flame. These images imply that the downstream part of the flame from RZ is maintained by small flame elements detached from RZ, and subsequent propagation eventually catches up the downstream flame formed by the previous event (see dotted line). With excessive quenching, a flame is confined to the cavity region of RZ.
Velocity vectors obtained from PIV tend to align tangentially with flame in many parts of flame front in the lower Figure, which could affect straining of the flame surface. Such alignment becomes less conspicuous as Re increases. This can be partially attributed to the competition of disturbances by turbulence and thermal expansion.​