A new experimental database for the investigation of soot in a model scale swirled combustor under perfectly premixed rich conditions M. Roussillo , P. Scouflaire S. Candel, B. Franzelli Proceedings of the Combustion Institute Dublin, 2018 EM2C lab, CNRS, CentraleSupélec,Université Paris-Saclay, 91192 Gif-sur-Yvette, France 1
Introduction Introduction 1) Soot are dangerous and harmful: Environment [2] TEM images of a soot Human health [3] particle [1] 2) But crucial role of soot in industrial burners Thermal radiation of soot is highly effective for glass or metal melting in large industrial applications Need for a better understanding of soot production to guide modeling efforts But there are numerous difficulties: Experimentally: small particles with high intermittency; optical properties not perfectly known and highly [1] Li, W., & Shao, L . (2009). Transmission electron microscopy study of aerosol particles from dependent on fuel and operating conditions the brown hazes in northern China . J. Geophys. Res. Atmos , 114 (D9). [2] T.C Bond et al. (2013) Bounding the role of black carbon in the climate system: A scientific assessment. J. Numerically: multi-physics and multi-scale Geophys. Res. Atmos ., 118, 5380–5552, [3] Pascal M et al. (2016) Impacts de l’exposition chronique aux particules fines sur la mortalité en France phenomenon continentale et analyse des gains en santé de plusieurs scénarios de réduction de la pollution atmosphérique Santé publique France
Introduction Numerous studies already exist on soot characterization: A) Laminar diffusion flame [1] /good predictability [1] B) Laminar premixed flame [2] /good predictability [3] C) Turbulent diffusion flame [4] /difficult challenge (f v ) [5] B C A D) Turbulent premixed flame: no experimental data and a single LES of a turbulent premixed sooting flame [6] But this configuration presents several advantages: No air/fuel mixing effect direct study of effects such as equivalence ratio or turbulence on soot production Perfectly premixed condition is interesting for numerical validation Useful for Rich-Quench-Lean concepts for NOx reduction [4] Geigle, K. P.et al, 2011. Experimental analysis of [1] Smooke, M., et al , 2005. Soot formation in laminar diffusion flame. soot formation and oxidation in a gas turbine model Combust. Flame , 143 (4), pp. 613–628. combustor using laser diagnostics. [2] Betrancourt, C. et al , 2017. Investigation of the size of the incandescent incipient J. Eng. Gas Turbines Power , 133 (12). soot particles in premixed sooting and nucleation flames [5] Rodrigues, P. et al, 2018. Coupling an LES approach and a soot of n-butane using LII, HIM, and 1 nm-SMPS. Aerosol Sci. sectional model for the study of sooting turbulent non-premixed flames. Technol. , 51 (8), pp. 916–935. Combust. Flame , 190, 477-499. [3] Abid, A.D. , et al, 2009. Quantitative measurement of soot particle size distribution in 3 premixed flames–the burner-stabilized stagnation flame approach. Combust. Flame [6] El-Asrag, H. et al, 2007. Simulation of soot formation in turbulent premixed flames. Combust. Flame , 150 (1-2), 108-126. 156.10 : 1862-1870.
Contet Introduction 1) EM2Soot configuration 2) Study of a typical operating point 3) Effects of operating conditions on soot production 4
EM2Soot configuraton Characteristics: Perfectly premixed (ethylene/air) swirled flame Quartz confinement 12 thermocouples for wall and gas temperature measurements Several challenges: 105 Stabilization of a rich premixed swirled flame with a new injector design Important role of the combustion chamber temperature (issue for repeatability) Fast obscuration of quartz (< 2 min) Relatively low soot volume fraction (detection issues) Injector design 5
Content 1) EM2Soot configuration 2) Study of a typical point (P =15 kW, φ =2.1) Laser Induced Incandescence (LII) for soot volume fraction Light scattering for soot imaging PIV for flow velocity measurements OH chemiluminescence for flame reaction zone 3) Effects of operating conditions on soot production 6
Soot volume fraction measurements (LII) [1] Δ x = 0.1 mm/pixel f v [ppb] 40 35 30 25 20 15 10 Wrinkled filament of soot visible along the wall with large-scale soot structure High temporal and spatial intermittency Δ x = 0.05 mm/pixel Strong interaction with turbulent eddies Ligamentary structure (thickness ≈ 1 mm) [1] Roussillo, M. et al. , 2018. “Experimental investigation of soot production in a confined swirled flame operating under perfectly premixed rich conditions ”. Proc. Combust. Inst (2018) 7 -4 -3 -2 -1 0
Soot volume fraction measurements (LII) [1] 16 Light scattering signal in the middle is But …. detected 14 f v [ppb] 40 12 Simultaneous 35 LII (red)/light 10 HAB [cm] scattering 30 (black) 8 experiments 25 at 532 nm 6 20 4 15 Soot is also present in the central region, two possibilities: 10 2 Small number of large particles 0 Big number of nuclei -4 -2 0 2 4 Soot volume fraction measurements (LII) r [cm] [1] What about mean soot volume fraction LII signal (soot volume fraction) is along the wall ? mainly detected close to the wall 8
Soot volume fraction measurements (LII) [1] 1000 f v = 7 . 7 ppb Mean soot volume fraction • Small intermittency 100 σ = 6 . 1 ppb distribution is monotonic along HAB? -1 ] 18 PDF [ppm 10 • High intermittency • Small f v variability 1 • Highest f v variability 16 0.1 f v [ppb] • Most probable value of f v 0.01 0.00 0.00 0.05 0.10 0.15 0.20 14 f v [ppm] ε =7.5 ppb 1000 10 f v = 6 . 6 ppb 12 100 σ = 7 . 1 ppb • High intermittency -1 ] HAB [cm] 1000 PDF [ppm 10 10 f v = 9 . 1 ppb 8 • Small f v variability 1 100 σ = 13 . 6 ppb 8 0.1 -1 ] 6 0.01 0.00 0.00 0.05 0.10 0.15 0.20 PDF [ppm 10 f v [ppm] 6 1000 • High intermittency f v = 9 . 1 ppb 4 4 1 100 σ = 13 . 6 ppb • Highest f v variability -1 ] PDF [ppm 10 2 0.1 1 2 0.1 0 0.01 -4 -2 0 2 4 0.01 0.00 0.05 0.10 0.15 0.20 r [cm] 0.00 0.05 0.10 0.15 0.20 f v [ppm] f v [ppm] Mean soot volume fraction from 300 uncorrelated images 9
Intermi,ency affects results interpreta5on 18 Weighted mean to account for the intermittency index I ε =7.5 ppb 16 ˜ f v [ppb] P N t 14 t =1 f v ( x, y, t ) I ( x, y, t ) e f v ( x, y ) = P N t 16 12 t =1 I ( x, y, t ) HAB [cm] 14 ⇢ 0 10 if f v ( x, y, t ) < ✏ I ( x, y, t ) = 12 8 1 if f v ( x, y, t ) ≥ ✏ 6 10 Intermittency has a major impact on 4 8 soot production è the weighted mean 2 is evolving monotonically in the axial 6 direction 0 -4 -2 0 2 4 r [cm] 10
PIV results PIV measurements under reactive conditions are carried out using soot particles as tracers A narrow band filter is used to filter out high flame luminosity on the second frame f Adaptive algorithm with Δ =75 µ s Two recirculation zones are present that correspond to the area of high soot volume fraction Flow is characteristic of a toroidal swirled flame that expands in the lateral direction and occupies a region located near the combustor bottom plane [1] [1] Degeneve, A. et al, 2018. ASME 2018 (2018) 11
Information on the flame reaction zone OH OH * (UA) ϕ =1.48 (non sooting) 12 3500 10 3000 Reaction zone close to the injector 8 2500 backplane with this injector design [1] HAB [cm] 2000 6 1500 4 OH detection is no longer possible due to : 1000 2 500 0 Low OH concentration for rich 0 -4 -2 0 2 4 r [cm] conditions ϕ =1.7 (sooting) Black body radiation of soot particles riche phi=1.672 and filter parasitic transmission in 12 infrared (rebound) 1] 2500 10 2000 Hypothesis: OH reaction zone remains 8 HAB [cm] 1500 close to the injector backplane for all the 6 1000 operating conditions 4 2 [1] Jourdaine, P et al “Effect of quarl on N2 -and 500 CO2 -diluted methane oxy-flames stabilized by an axialplus- tangential swirler”. In ASME Turbo Expo 2016: Turbomachinery 0 Technical Conference and Exposition [2] Panoutsos, C.et al. , 2009. “Numerical evaluation of equivalence ratio -4 -2 0 2 4 measurement using OH and CH chemiluminescence in premixed and nonpremixed methane–air r [cm] flames”. Combust. Flame , 156 (2), pp. 273–291 12
Content 1) EM2Soot configuration 2) Study of a typical operating point 3) Effects of operating conditions on soot production 13
Effect of wall temperature [1] Effect of wall temperature [1] Temperature (T c ) is reached after preheating of the chamber with a lean flame T c [K] T c [K] 270 320 370 420 470 520 570 620 670 Strong link between the wall temperature on soot production detected both qualitatively and quantitatively All experiments are then carried out with an initial temperature of T c =570 K, assuring a good repeatability, a sufficient soot production and a quasi-steady thermal state during experiments Δ T= 15 K [1] Roussillo, M. et al, 2017. “A new experimental database for the investigation of soot in a model scale swirled combustor under perfectly premixed rich conditions”. 14 ASME 2018 (2018)
Effect of equivalence ratio ϕ A critical equivalence ratio for maximum soot production close to 2.1 is measured Fair agreement between LII measurements and visual aspect of flame evolution with the equivalence ratio Scalable for all studied powers ϕ 15
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