简介:This paper presents observations and analysis of the time-dependent behaviour of a 10 kW
partially pre-mixed, swirl stabilized methane-air flame exhibiting self-excited thermo-acoustic
oscillations. This analysis is ba简介:This paper presents observations and analysis of the time-dependent behaviour of a 10 kW
partially pre-mixed, swirl stabilized methane-air flame exhibiting self-excited thermo-acoustic
oscillations. This analysis is based on a series of measurements wherein particle image
velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical were
performed simultaneously at 5 kHz repetition rate over durations of 0.8s. Chemiluminescence
imaging of the OH* radical was performed separately, also at 5 kHz over 0.8s acquisition
runs. These measurements were of sufficient sampling frequency and duration to extract
usable spatial and temporal frequency information on the medium to large-scale flow-field
and heat-release characteristics of the flame. This analysis is used to more fully characterize
the interaction between the self-excited thermo-acoustic oscillations and the dominant flowfield
structure of this flame, a precessing vortex core (PVC) present in the inner recirculation
zone. Interpretation of individual measurement sequences yielded insight into various
physical phenomena and the underlying mechanisms driving flame dynamics. It is observed
for this flame that location of the reaction zone tracks large-scale fluctuations in axial velocity
and also conforms to the passage of large-scale vortical structures through the flow-field.
Local extinction of the reaction zone in regions of persistently high principal compressive
strain is observed. Such extinctions, however, are seen to be self healing and thus do not
induce blow-out. Indications of auto-ignition in regions of unburned gas near the exit are also
observed. Probable auto-ignition events are frequently observed coincident with the centers of
large-scale vortical structures, suggesting the phenomenon is linked to the enhanced mixing
and longer residence times associated with fluid at the core of the PVC as it moves through
the flame.详细>