Ghent University - UGent Department of Flow, Heat and Combustion Mechanics FloHeaCom.UGent.be

1. Simulations of hydrogen auto-ignitionIvana Stanković1 and Bart Merci 1 1Ghent University, Belgium; contact: Ivana.Stankovic@UGent.be 1. Introduction 2. LES - CMC • 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. 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. • 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. 3. Test case: hydrogen auto-ignition [1] 4. Numerical set-up and boundary conditions Lign – Ignition length; Lmin – minimum ignition length 5. Results Instantaneous resolved temperature (T) and mass fraction (Y) fields [2]. Outer isoline: most reactivemixture fraction - ηmr ; Inner isoline: stoichiometric - ηst (Tcf = 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: 6. Conclusions • 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 Tcf and increases with increase in ucf. • 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 HO2 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 Ghent University - UGent Department of Flow, Heat and Combustion Mechanics www.FloHeaCom.UGent.be