1. Experimental study of the spontaneous ignition of partly confined hydrogen jets Brian Maxwell, Patrick Tawagi, and Matei Radulescu Department of Mechanical Engineering University of Ottawa International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA ID: 216

2. Diffusion-Ignition International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA Previous experiments[2-7] have shown that when pressurized H2 is suddenly released into air, spontaneous ignition of the jet can occur through shock induced diffusion-ignition. 2.Wolanski & Wojcicki (1973) 3.Dryer et al. (2007) 4. Golovastov et al. (2009) 5.Mogi et al. (2009) 6. Oleszczak & Wolanksi (2010) 7. Lee et al. (2011)

3. Diffusion-Ignition Several numerical investigations[8-16] have identified this mechanism as responsible for generating localized combustion 'hot spots'. International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA Temperature (K)OHSource: Wen et al. (2009)

4. Confined Releases The experiments [3-7] have only been able to identify ignition limits for releases providing the H 2 is first released through some partly confining tube. International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA Source: Mogi et al. (2009)

5. Confined Releases Confined releases are believed to be more likely to ignite due to: Release in a tube prevents global expansion (cooling) of the the gas Local heating in the boundary layer of the tube Richtmyer-Meshkov instability in the tube International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA Source: Dryer et al. (2007)

6. Objective To examine the role of turbulent mixing on the jet and how it influences ignition Experimental approach (which scales up the release to examine what happens inside a tube for example) Results may also be useful for benchmarking future numerical studies Preliminary Numerical investigation International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

7. Experimental Setup International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA Schlieren photography setup to capture flow-field evolution Direct time resolved self-luminosity photographs to capture combustion d=20mm or 67mm

8. Experimental Results International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA a)Schlieren photograph of igniting jet. b)Direct photograph capturing ignition. c)Combustion at a later time...

9. Experimental Results International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA Ignition limit (shock in O2): d=67mm, M=4.6+/-0.4 d=20mm, M=5.1+/-0.3

10. Numerical Simulation Numerical reconstruction of the flow-field (Video) Perfect gas Euler Equations (Inviscid, non-reactive) International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

11. Numerical Simulation International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

12. Numerical Simulation International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

13. Ignition Limits International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA More details can be found in Maxwell B. M., and Radulescu M.I. (2011). Combustion and Flame doi:10.1016/j.combustflame.2011.03.001 (In press) Ignition limits are estimated for unconfined release using a one dimensional model that follows the diffusion layer at the head of the jet as it is convected away from the release point.

14. Ignition Limits International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

15. Ignition Limits International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

16. Conclusions Ignition limits of partially confined releases depend strongly on: Strength of shock wave Size of release hole Confinement does not have a major impact on whether or not local ignition spots will form on the jet surface. International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

17. Conclusions RM and KH instabilities lead to increased turbulent mixing causing much more gas to be ignited than previously predicted by CFD. Reflected shock waves play a major role influencing turbulent mixing (i.e. how ignition 'hot spots' interact leading to full jet ignition) International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

18. Acknowledgment The present work was sponsored by – NSERC Discovery grant – NSERC Hydrogen Canada (H2CAN) Strategic Research Network – Ontario Graduate Scholarship International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA

19. References International Conference on Hydrogen Safety September 12-14, 2011 San Francisco, USA 1. Groethe M., Merilo E., Colton J., Chiba S., Sato Y., and Iwabuchi H. (2007) Int. J. Hydrogen Energy 32: 2125-2133. 2. Wolanski P. and Wojcicki S. (1973). 14th Symp. (Int.) on Combustion, Pittsburg, PA 1217-1223. 3. Dryer F. L., Chaos M., Zhao Z., Stein J. N., Alpert J. Y., and Homer C. J. (2007). Combust. Sci. Tech. 179: 663-694. 4. Golovastov S. V., Baklanov D. I., Volodin V. V., Golub V. V., and Ivanov K. V. (2009). Russ. J. Phys. Chem. B 3 No. 3: 348-355. 5. Mogi T., Wada Y., Ogata Y., and Hayashi A. K. (2009). Int. J. Hydrogen Energy 34: 5810-5816. 6. Oleszczak P. and Wolanski P. (2010). Shock Waves 20:539-550. 7. Lee H.J., Kim Y.R., Kim S.H., and Jeung I.S. (2011). Proceedings of the Combustion Institute 33: 2351-2358. 8. Maxwell B. M., and Radulescu M.I. (2011). Combust. Flame doi: 10.1016/j.combustflame.2011.03.001 (In press) 9. Liu Y. F., Tsuboi F. N., Sato H., Higashino F, and Hayashi A. K. (2005). 20th Intl Colloquium on the Dynamics of Explosions and Reactive Systems, Montreal, Canada. 10. Liu Y. L., Zheng J. Y., Xu P., Zhao Y. Z., Bei H. Y., Chen H. G., and Dryver H. (2009). Journal of Loss Prevention in the Process Industries 22: 265-270. 11. Xu B. P., Hima L. E. L., Wen J. X., and Tam V. H. Y. (2009). Int. J. Hydrogen Energy 34 No. 14: 5954-5960. 12. Wen J. X., Xu B. P., and Tam V. H. Y. (2009). Combust. Flame 156: 2173-2189. 13. Xu B. P., Hima L. E., Wen J. X., Dembele S., Tam V. H. Y., and Donchev T. (2008). Journal of Loss Prevention in the Process Industries 21: 205-213. 14. Yamada E., Kitabayashi N., Hayashi A. K., and Tsuboi N. (2011). Int. J. Hydrogen Energy 36: 2560-2566. 15. Lee B.J., and Jeung I. (2009). Int. J. Hydrogen Energy 34: 8763-8769. 16. Bragin M.V., and Molkov V.V. (2011). Int. J. Hydrogen Energy 36: 2589-2596.