简介:This article concerns the flame dynamics of a bluff body stabilized turbulent premixed flame as it
approaches lean blowoff. Time resolved chemiluminescence imaging along with simultaneous particle
image velocimetry and简介:This article concerns the flame dynamics of a bluff body stabilized turbulent premixed flame as it
approaches lean blowoff. Time resolved chemiluminescence imaging along with simultaneous particle
image velocimetry and OH planar laser-induced fluorescence were utilized in an axisymmetric bluff body
stabilized, propane-air flame to determine the sequence of events leading to blowoff and provide a quantitative
analysis of the experimental results. It was found that as lean blowoff is approached by reduction
of equivalence ratio, flame speed decreases and the flame shape progressively changes from a conical to a
columnar shape. For a stably burning conical flame away from blowoff, the flame front envelopes the
shear layer vortices. Near blowoff, the columnar flame front and shear layer vortices overlap to induce
high local stretch rates that exceed the extinction stretch rates instantaneously and in the mean, resulting
in local flame extinction along the shear layers. Following shear layer extinction, fresh reactants can pass
through the shear layers to react within the recirculation zone with all other parts of the flame extinguished.
This flame kernel within the recirculation zone may survive for a few milliseconds and can reignite
the shear layers such that the entire flame is reestablished for a short period. This extinction and
reignition event can happen several times before final blowoff which occurs when the flame kernel fails
to reignite the shear layers and ultimately leads to total flame extinguishment.详细>