Ghent University - UGent Department of Flow, Heat and Combustion Mechanics Simulations of hydrogen...

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

www.FloHeaCom.UGent.be

Simulations of hydrogen auto-ignitionIvana Stanković1 and Bart Merci 1

1Ghent University, Belgium; contact: Ivana.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

LES CMC

Mesh (cells) 192 x 48 x 48 80 x 8 x 8

Solution domain [mm] 67.5 x 25 x 25

Fuel composition Y(H2) = 0.13; Y(N2) = 0.87

Co-flow (cf) Air

Velocities [m/s] ufuel = 120; ucf = 20-35

Temperatures [K] Tfuel= 691; Tcf = 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 - 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:

• 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

• 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.

Lign – Ignition length; Lmin – 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.