Soot volume fraction fields in unsteady axis-symmetric flames by continuous laser extinction technique

Abstract

A Laser Extinction Method has been set up to provide two-dimensional soot volume fraction field time history at a tunable frequency up to 70 Hz inside an axis-symmetric diffusion flame experiencing slow unsteady phenomena preserving the symmetry. The use of a continuous wave laser as the light source enables this repetition rate, which is an incremental advance in the laser extinction technique. The technique is shown to allow a fine description of the soot volume fraction field in a flickering flame exhibiting a 12.6 Hz flickering phenomenon. Within this range of repetition rate, the technique and its subsequent post-processing require neither any method for time-domain reconstruction nor any correction for energy intrusion. Possibly complemented by such a reconstruction method, the technique should support further soot volume fraction database in oscillating flames that exhibit characteristic times relevant to the current efforts in the validation of soot processes modeling.

Sooting propensities of some gasoline surrogate fuels: Combined effects of fuel blending and air vitiation

“…24. The diffusion flames are established over an axis-symmetric coflow burner identical to the one described by Santoro et al [26] and used in previous investigations 6 [24,27,28]. In the following, the axis of symmetry is (Oz) and its origin is located at the burner tip, defining the height above the burner (HAB).…”

“…Kashif et al [27] provides with the two-dimensional soot volume fraction fields f v (r, z) required to evaluate the different kinds of f v,max and input them in Eq. (1).…”

“…A frame grabber records the frames captured by the camera on a 8 computer. As a line-of-sight technique, LEM is combined with a subsequent deconvolution that incorporates a Tikhonov regularization [27]. The local extinction coefficient distribution  ext (r, z) can then be computed from the projected data, i.e.…”

“…the field of extinction coefficient integrated along the lineof-sight. This LEM technique has been shown to provide both fine temporal and spatial resolutions [27].…”

Fire safety in space – Investigating flame spread interaction over wires

“…This provided a sequence of pairs of frames, one imaging the backlighting together with the flame spontaneous emission, the following one capturing only the flame's spontaneous emission. Subtracting the latter from the former allows the absorption field through the flame to be inferred [27]. The LEDs were switched on 5 ms before the CCD exposure was requested, and were then switched off 5 ms after the CCD exposure was terminated.…”