1. Ghent University - UGent Department of Flow, Heat and Combustion Mechanics www.FloHeaCom.UGent.be Simulations of hydrogen auto-ignition Ivana Stanković 1 and Bart Merci 1 1 Ghent University, Belgium; contact: Ivana.Stankovic@UGent.beIvana.Stankovic@UGent.be 5. Results 2. LES - CMC 3. Test case: hydrogen auto-ignition [1] 1. Introduction Schematic of the interface of the LES and CMC codes Large Eddy Simulation (LES) – for accurate turbulence representation. Conditional Moment Closure (CMC) – combustion model, allows us to include detailed chemistry mechanism and turbulence- chemistry interactions. Goals: to couple LES and CMC; to apply it to hydrogen auto- ignition case; to investigate stabilization mechanism and influence of different chemical mechanisms. 4. Numerical set-up and boundary conditions 6. Conclusions LESCMC Mesh (cells)192 x 48 x 4880 x 8 x 8 Solution domain [mm]67.5 x 25 x 25 Fuel compositionY(H 2 ) = 0.13; Y(N 2 ) = 0.87 Co-flow (cf)Air Velocities [m/s]u fuel = 120; u cf = 20-35 Temperatures [K] T fuel = 691; T cf = 935-980 References [1] C.N. Markides and E. Mastorakos, Proc. Combust. Inst. 30 (2005) 883-891. [2] I. Stanković, A. Triantafyllidis, E. Mastorakos, C. Lacor, B. Merci, Flow Turbul. Combust. (2010), doi: 10.1007/s10494-010-9277-0 [3] J. Li, Z. Zhao, A. Kazakov and F.L. Dryer, Int. J. Chem. Kinet. 36 (2004) 566-575. [4] R.A. Yetter, F.L. Dryer and H. Rabitz, Combust. Sci. and Tech. 79 (1991) 97-128. [5] M.A. Mueller, T.J. Kim, R.A. Yetter and F.L. Dryer, Int. J. Chem. Kinet. 31 (1999) 113-125. Instantaneous resolved temperature (T) and mass fraction (Y) fields [2]. Outer isoline: most reactive mixture fraction - η mr ; Inner isoline: stoichiometric - η st (T cf = 960K, Li et al. [3]): Auto-ignition length for different chemical mechanisms (Li et al. [3], Yetter et al. [4] and Mueller et al. [5]), experimental data shifted by 60K: LES-CMC approach is successful in reproducing hydrogen auto-ignition case where turbulence and chemistry are of equal importance. The results are qualitatively consistent with experimental data. The auto-ignition length decreases with an increase in T cf and increases with increase in u cf. Different chemical mechanism are tested: they exhibit a similar qualitative behaviour but require different boundary conditions in order to yield the same lift-off height. Stabilization mechanism: auto-ignition – shown by the build up of HO 2 ahead of the reaction zone at the lean side. Acknowledgments:This project is in collaboration with Vrije Universiteit Brussel – VUB and Department of Engineering – Hopkinson Laboratory, Cambrige University Further development of combustion devices (e.g. low NOx diesel, homogeneous charge compression engines) depends on ability to understand auto-ignition and its stabilization in turbulent flows. Any method for accurately predicting auto-ignition phenomena must incorporate turbulence, unsteady chemistry and detailed mechanisms. L ign – Ignition length; L min – minimum ignition length Flow field: velocities, mixture fraction, mixture fraction variance, conditional or unconditional scalar dissipation rate. Based on composition and temperature conditional density is calculated. Coupling between LES and CMC is done thorough density. Knowing density, the flow field in LES can be updated.