LES of Spray Combustion using Flamelet Generated Manifolds Armin Wehrfritz, Ville Vuorinen, Ossi Kaario and Martti Larmi armin.wehrfritz@aalto.fi Aalto University Thermodynamics and Combustion technology April 07, 2014
Part I: Non-reacting spray study Objectives 1. Mesh resolution effects in Large Eddy Simulation 2. Influence of droplet breakup modeling on the local and global flow characteristics Spray case Non-reacting Spray A baseline: P inj = 150 MPa T = 900 K P amb = 6 MPa 0 % O 2 Reference, V. Vuorinen, O. Kaario, and M. Larmi., Large Eddy Simulation of High-Velocity Fuel Sprays: Studying Mesh Resolution and Breakup Model Effects for Spray A. Atomization and Sprays, 23(5):419 442, 2013. LES of Spray Combustion using FGM 2/15
Computational Methods Gas phase Large Eddy Simulation (LES) Turbulence modeling based on the implicit LES approach [2] No explicit subgrid scale model Finite Volume, open source CFD code OpenFOAM 2.0.x (2nd order accurate in space and time) Liquid phase Lagrangian Particle Tracking (LPT) No explicit primary break-up model Initial droplet size distribution (Rosin-Rammler) Secondary break-up models: 1. Enhance Taylor Analogy Breakup (ETAB) 2. Kelvin-Helmholtz Rayleigh-Taylor (KHRT) LES of Spray Combustion using FGM 3/15
Computational mesh Fully hexahedral Refinement in the spray region by 2:1 cell splitting Applied cell sizes: dx [µm] N cells [-] 250 0.8M 125 1.2M 62.5 4.8M 41.67 16.2M Constant time step: t = 1 10 8 s LES of Spray Combustion using FGM 4/15
Results Liquid length Poor results for 250 µm cell size meshes, regardless of breakup model 125 µm cell size: ETAB: Good agreement with experiments KHRT: Significantly over-predicted Good results for 62.5 and 41.67 µm cell size meshes, regardless of breakup model (a) ETAB (b) KHRT Liquid penetration [mm] Liquid penetration [mm] 30 25 20 15 10 Experiments 250 µm 5 125 µm 62.5 µm 41.67 µm 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time [ms] 30 25 20 15 10 Experiments 250 µm 5 125 µm 62.5 µm 41.67 µm 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time [ms]
Results Mixture fraction distribution (KHRT model) 250 µm cell size mesh not able to capture the turbulent motion correctly 125 µm cell size mesh able to capture a significant part of the turbulent motion Increasing level of detail for 62.5 and 41.67 µm cell size meshes 250 µm 125 µm 62.5 µm 41.67 µm
Results Vapor penetration (KHRT:, ETAB: no marker) Slight under-prediction for all cell sizes and both breakup models Vapor penetration [mm] 60 50 40 30 20 10 Experiments 125 µm 62.5 µm 41.67 µm Radial mixture fraction profile (KHRT:, ETAB: no marker; z = 25 mm) 125 and 62.5 µm mesh: Values in the the center is under- and spreading over-predict 41.67 µm mesh: Good agreement with experiments Vapor mass frac. [-] 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time [ms] 0.15 0.10 0.05 0.00 Experiments 125 µm 62.5 µm 41.67 µm 0 2 4 6 8 10 r [mm]
Results PDF of droplet diameter 0.12 0.10 ETAB 125 µm 62.5 µm 41.67 µm ETAB model Uniform distribution SMD = 0.3 µm... 0.4 µm PDF 0.08 0.06 0.04 0.02 KHRT KHRT model Broad range of droplet sizes SMD = 1.1 µm... 1.4 µm 0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 d [µm] Probability density function of droplet diameter at t = 1.4 ms
Part II: Non-reacting spray study Objectives: Investigate the ignition characteristics and and early flame structure using Large Eddy Simulation and Flamelet Generated Manifold (FGM) Spray case Reacting Spray A cases: P inj = 150 MPa T = 900 K P amb 6 MPa ρ amb = 22.8 kg/m 3 15 % O 2 LES of Spray Combustion using FGM 9/15
Computational Methods Flow solver Implicit Large Eddy Simulation Lagrangian Particle Tracking (Secondary breakup: ETAB) OpenFOAM 2.2.x Advanced thermodynamic/transport models (i.e. Wilke/Mathur mixture models) Flamelet Generated Manifolds (FGM) [3] Tabulated chemistry model State of combustion is parametrized by a few control variables (here, mixture fraction and a reaction progress variable) Chemistry data obtained from 1D igniting/steady counterflow diffusion flames (i.e. flamelets) Detailed chemical kinetics (253 species, 1437 reactions [4]) LES of Spray Combustion using FGM 10/15
FGM tables C [-] 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 Z [-] 2000 1750 1500 1250 1000 750 500 C [-] 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 Z [-] 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 Figure : Temperature Figure : CO mass fraction Chemistry parametrized by mixture fraction Z and reaction progress variable C LES of Spray Combustion using FGM 11/15
Results Spray penetration Calculation are carried out on the 62.5 µm mesh Simulated liquid length matches the experimental data Vapor penetration slightly under-predicted Spray penetration [mm] 50 40 30 20 10 Experiments Simulation 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time [ms]
Results Ignition delay Significant over-prediction compared to experiments Consistent ignition delay estimate for both ECN definitions ( dt dt & OH mass fraction) Flame length Lift-off length slightly under-predicted T [K] Spray flame penetration [mm] 2400 2200 2000 1800 1600 1400 1200 1000 Temperature 800 0.0 0.2 0.4 0.6 0.8 1.0 t [ms] 45 40 35 30 25 20 15 10 5 Experiments Lift-off length Jet penetration (Zst = 0.045) Ignition OH Experiments 1e 4 0 0.0 0.2 0.4 0.6 0.8 1.0 t [ms] 8 6 OH [-] 4 2 0
Results Spray A combustion
Questions & Discussion Thank you for your attention! LES of Spray Combustion using FGM 15/15
1 Appendix LES of Spray Combustion using FGM 1/4
1 References [1] Armin Wehrfritz, Ville Vuorinen, Ossi Kaario, and Martti Larmi. Large Eddy Simulation of High-Velocity Fuel Sprays: Studying Mesh Resolution and Breakup Model Effects for Spray A. Atomization and Sprays, 23(5):419 442, 2013. ISSN 1044-5110. doi: 10.1615/AtomizSpr.2013007342. URL http://www.dl.begellhouse.com/journals/ 6a7c7e10642258cc,67b312a93f7dc969, 0a7117ff52a01272.html. [2] F. F. Grinstein, L. G. Margolin, and W. J. Rider. Implicit Large Eddy Simulation. Cambridge University Press, 2007. ISBN 978-0-521-86982-9. LES of Spray Combustion using FGM 2/4
1 References II [3] J. A. van Oijen and L. P. H. de Goey. Modelling of Premixed Laminar Flames using Flamelet-Generated Manifolds. Combustion Science and Technology, 161(1):113 137, December 2000. ISSN 0010-2202, 1563-521X. doi: 10.1080/00102200008935814. URL http://www. tandfonline.com/doi/abs/10.1080/00102200008935814. LES of Spray Combustion using FGM 3/4
1 References III [4] Krithika Narayanaswamy, Perrine Pepiot, and Heinz Pitsch. A chemical mechanism for low to high temperature oxidation of n-dodecane as a component of transportation fuel surrogates. Combustion and Flame, 161(4):866 884, April 2014. ISSN 0010-2180. doi: 10.1016/j.combustflame.2013.10.012. URL http://www.sciencedirect.com/science/article/pii/ S0010218013003866. LES of Spray Combustion using FGM 4/4