Planar laser-induced incandescence of turbulent sooting flames: the influence of beam steering and signal trapping

Sun, Zhiwei; Alwahabi, Zeyad T.; Gu, Dahe; Mahmoud, Saleh; Nathan, Graham J.; Dally, Bassam B.

doi:10.1007/s00340-015-6080-6

Cited by 31 publications

(19 citation statements)

References 40 publications

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“…Asymmetric soot volume fraction profiles have been reported in several previous studies [24,35]. Recent study by Nathan, Dally, and coworkers [36] suggested that beam steering can alter the distribution of local fluence in the laser beam sheet and thus cause this asymmetry, although we can observe asymmetry in the visible luminosity at the flame base, which does suggest there is a natural asymmetry in the soot formation. Soot is predominantly formed within the temperature band of 1100-1500 K on the fuel-rich side and peak f v is formed between the temperature bands of 1300-1400 K. Previous work by others in pure C 2 H 4 jet flames has shown that soot exists in the temperature range of 1200-1800 K, with the peak f v occurring in the temperature range of 1500-1600 K [37,38].…”

Section: Resultssupporting

confidence: 64%

Mixture fraction, soot volume fraction, and velocity imaging in the soot-inception region of a turbulent non-premixed jet flame

Park

Burns

Buxton

et al. 2017

Proceedings of the Combustion Institute

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An experimental study is performed to investigate the feasibility of conducting simultaneous mixture fraction, soot volume fraction and velocity imaging in sooting jet flames. The measurements are performed in the soot-inception region of ethylene jet flames, where the yellow luminous region first appears in the flame. Three-component velocity and soot volume fraction are measured by stereoscopic particle image velocimetry and laser-induced incandescence, respectively. The mixture fraction is inferred from laser-induced fluorescence of krypton gas seeded into the fuel stream. To obtain mixture fraction from the fluorescence signal, the signal must be corrected for density and fluorescence quenching effects. This correction is accomplished by invoking an assumed state relationship that is derived from a laminar strained-flame calculation. Once properly calibrated, the krypton planar laserinduced fluorescence data give the mixture fraction, temperature and major species near the regions of soot formation. The krypton is seeded into the fuel jet at a mole fraction of approximately 4%. The fluorescence of krypton is achieved by two-photon absorption at 214.7 nm and the resulting fluorescence is collected at 760.2 nm. The krypton fluorescence signal is rather weak, particularly near the reaction zones where density is lowest, and so adequate signal-to-noise ratios could be achieved in a sheet only about 1 mm in height, which effectively limited this study to a line measurement of mixture fraction. The temperature field derived from the mixture fraction field was compared to temperatures obtained from thermocouple measurements. The mean radial temperature profiles using the different techniques show excellent agreement and this serves to validate the methodology used to map from fluorescence signal to mixture fraction and temperature. The resulting data are of high enough quality as to allow the investigation of the kinematics, thermo-chemical state and even the dissipation fields near regions of soot formation.

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Section: Resultssupporting

confidence: 64%

Mixture fraction, soot volume fraction, and velocity imaging in the soot-inception region of a turbulent non-premixed jet flame

Park

Burns

Buxton

et al. 2017

Proceedings of the Combustion Institute

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“…The laser fluence was kept above 0.5 J/cm 2 , in the plateau region of the LII response curve, to minimize any influence on the LII signal due to fluence variation from attenuation or from beam "steering". The influence of beam steering and signal trapping on the accuracy of soot volume fraction has been fully investigated in turbulent non-premixed sooting flames by Sun et al [15]. The maximum "steering" of the laser beams in the flames was measured to be 2 milli-rad, corresponding to a 50% increase in the laser sheet thickness from one side of the flame to the other.…”

Section: Laser Induced Incandescence (Lii)mentioning

confidence: 99%

The effect of exit strain rate on soot volume fraction in turbulent non-premixed jet flames

Mahmoud

Nathan

Alwahabi

et al. 2017

Proceedings of the Combustion Institute

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Section: Introductionmentioning

confidence: 87%

“…The extent of beam steering in LII measurements has been reported in depth by Zerbs et al [18] and Sun et al [19] for turbulent ethylene jet flames, reporting that f v can be underestimated by 30% because of variation in the local fluence. This effect even occurs in the plateau excitation regime [19], where the effect could be expected to be less significant due to the reduced impact of the fluence. Furthermore, the impact of beam steering is significant in both reacting and non-reacting flows [19] and is substantial at higher pressures, because the gradient in the refractive index becomes steeper [18].…”

Section: Introductionmentioning

confidence: 87%

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The significance of beam steering on laser-induced incandescence measurements in laminar counterflow flames

et al. 2018

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Beam steering is often encountered in laser diagnostic measurements, especially in flame environments, due to changes in refractive index caused by thermal and species gradients. It can negatively affect the accuracy of the results. In this work, the effects of beam steering on laser-induced incandescence (LII) measurements of pre-vaporized-liquid counterflow flames are assessed. The focus on counterflow flames is to facilitate future detailed experimental campaigns on one-dimensional nonpremixed sooty flames. It is found that the temperature and species gradients in the counterflow configuration have a much more significant impact on the beam profile than in laminar flat flames, especially for heavier fuels. As a result of the changes in the beam profile, for the same applied laser energy, the local fluence shifts markedly with fuel type, therefore, having a direct impact on the LII measurements. A procedure is developed for ensuring accurate measurements and it is shown that, for a specific fuel, it is possible to tailor the laser energy, such that the collected LII signal in the counterflow flames is nearly independent of beam-steering effects.

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Planar laser-induced incandescence of turbulent sooting flames: the influence of beam steering and signal trapping

Cited by 31 publications

References 40 publications

Mixture fraction, soot volume fraction, and velocity imaging in the soot-inception region of a turbulent non-premixed jet flame

Mixture fraction, soot volume fraction, and velocity imaging in the soot-inception region of a turbulent non-premixed jet flame

The effect of exit strain rate on soot volume fraction in turbulent non-premixed jet flames

The significance of beam steering on laser-induced incandescence measurements in laminar counterflow flames

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