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Shock-initiated ignition for hydrogen mixtures of different concentrations

Shock-initiated ignition for hydrogen mixtures of different concentrations. Josue Melguizo-Gavilanes , & Luc Bauwens University of Calgary. 4 th International Conference on Hydrogen Safety San Francisco, CA USA September 12-14, 2011. Motivation.

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Shock-initiated ignition for hydrogen mixtures of different concentrations

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  1. Shock-initiated ignition for hydrogen mixtures of different concentrations JosueMelguizo-Gavilanes, & Luc Bauwens University of Calgary 4th International Conference on Hydrogen Safety San Francisco, CA USA September 12-14, 2011

  2. Motivation • Possible use of hydrogen as a fuel for transportation. • Hydrogen: burns without releasing CO2 + buoyant + detonates easily = ??? • Hydrogen storage and handling remains an issue (i.e. risk of detonation) • We need: Improved understanding of relevant scientific issues.

  3. Objectives • Relevant Scientific Issues • Clarification of the physics of shock-initiated ignition and detonation waves. • Study how chemical kinetics affect the ignition dynamics of combustible mixtures. • Relationship with deflagration to detonation transition (DDT). • Advance the understanding of the role played by chain-branching and its key features on DDT.

  4. Background • Two modes of combustion: Deflagrations and Detonations. • Deflagration: subsonic combustion wave • Detonation: supersonic combustion wave (reacting shock wave). • First experimental evidence of detonations in 1881 by Berthelot & Vieille and by Mallard & Le Châtelier. • First theory in 1905 by Chapman and Jouguet, independently.

  5. Background • Two means of initiating a detonation • Direct Initiation & deflagration to detonation transition (DDT). • DDT • Ordinary, relatively slow flame, accelerates and suddenly turns into a much destructive detonation wave. • Difficult outstanding problem in combustion science. • Most likely means of initiating a detonation in an accidental explosion.

  6. The Problem • Numerical simulation of ignition behind a shock moving into combustible mixture. • Ignition behind leading shock, evolution and appearance of a detonation Sequence of events identified in many DDT scenarios. • Simulations Short & Dold (1996), Sharpe & Short (2004-2007), Sharpe & Maflahi (2006), Melguizo-Gavilanes et. al (2010) and others.

  7. Formulation: Governing equations & chemistry One dimensional Euler’s equations for reactive, inviscid, non-conducting flows Three-steps: Initiation, branching and termination heat release associated with termination only

  8. Formulation: Initial and Boundary Conditions • Left boundary: Fresh incoming combustible mixture • Conditions ahead of the shock given by: • λ1=1 & λ2=0 • Right boundary: Inert/burnt mixture • λ1=0 & λ2=0

  9. Formulation: Challenges • Initial conditions are singular at t=0, shock separates uniform supersonic flow of unburnt mixture from burnt/inert mixture • Non-existence of initial domain where chemistry takes place (shocked unburnt mixture) on spatial (x) grid

  10. Formulation: Transformation Transforming the problem from x and t as independent variables to and t yields a finite domain at t=0

  11. Formulation: Initial Conditions Normal Grid Transformed grid Normal grid

  12. Formulation: Initial Conditions • Ms=0.7011, ps=ρs=Ts=1.0, us= ub=0, Tb=4.0 • Plot of pressure at t=0 • Plot of temperature at t=0

  13. Formulation: Boundary Conditions • Left Boundary Condition: Fresh incoming combustible mixture • Right Boundary Condition: Burnt/inert mixture • Domain Length: On left, η < 0, smaller than the opposite of the speed of the shock. On right ηmax greater than the local speed of sound. • λ1=1 & λ2=0 • λ1=0 & λ2=0

  14. Numerical Scheme • Shock Capturing Scheme • Essentially Non-Oscillatory for space integration and Runge-Kutta for time integration (2nd Order Accurate) • Flux limiting near shocks • Parallelized using MPI (Message Passing Interface) • Proper implementation requires a careful derivation of the CFL condition • Short-time asymptotics is used to derive our initial conditions

  15. Results: Hot Spot Formation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 1: Hot spot formation for Q=2 at times t = 7.131, 7.727, 8.372, 8.714, and 9.071. Left: Pressure profiles. Right: Temperature profiles.

  16. Results: Hot Spot Formation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 2: Hot spot formation for Q=6 at times t = 7.131, 7.573, 7.727, 7.883, and 8.042. Left: Pressure profiles. Right: Temperature profiles.

  17. Results: Hot Spot Formation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 3: Hot spot formation for Q=8 at times t = 6.989, 7.276, 7.423, 7.573, and 7.727. Left: Pressure profiles. Right: Temperature profiles.

  18. Results: Transition to Detonation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 4: Transition to detonation for Q=2 at times t = 10.649, 11.538, 12.501, 13.545, 14.675, 15.901, 17.228 and 17.932. Left: Pressure profiles. Right: Temperature profiles.

  19. Results: Transition to Detonation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 5: Mass fraction profiles for Q=2 at times t = 10.649, 11.538, 12.501, 13.545, 14.675, 15.901, 17.228 and 17.932.

  20. Results: Transition to Detonation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 6: Transition to detonation for Q=6 at times t = 8.206, 8.372, 8.714, 9.071, 9.442, 10.230, 11.084, 12.009 and 13.012. Left: Pressure profiles. Right: Temperature profiles.

  21. Results: Transition to Detonation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 7: Mass fraction profiles for Q=6 at times t = 8.206, 8.372, 8.714, 9.071, 9.442, 10.230, 11.084, 12.009 and 13.012.

  22. Results: Transition to Detonation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 8: Transition to detonation for Q=8 at times t = 8.043, 8.372, 8.714, 9.442, 10.230, 11.084, and 12.009. Left: Pressure profiles. Right: Temperature profiles.

  23. Results: Transition to Detonation • γ=1.4, TB=0.9, EB=8.0, TI=3.0, EI=20 and 102,400 grid points Figure 9: Mass fraction profiles for Q=8 at times t = 8.043, 8.372, 8.714, 9.442, 10.230, 11.084, and 12.009.

  24. Conclusions • The scenario of shock-induced ignition was analyzed using a three-step chain-branching kinetic scheme which attempts to model properly the key feature of hydrogen mixtures. • Results show that as the heat release is increased: - ignition takes place faster. - the location where the secondary shock forms, and a fully developed detonation appears occurs closer to the contact surface. - The pressure and temperature maxima for both stages of the process, hot spot formation, and transition to detonation, attain higher values. • For all cases simulated, except for Q = 2, transition to detonation took place before merging of the resulting structure with the leading shock.

  25. Conclusions • The approach proposed was shown to be effective to tackle the difficult problem of shock-induced ignition. • The propagation of pressure and temperature disturbances, their steepening into a secondary shock, and subsequent transition to detonation was properly captured by our current framework.

  26. Acknowledgements • Work supported by the Natural Science and Engineering Research Council of Canada and the H2Can Strategic Network

  27. References [1] Sharpe, G.J. and Short, M. (2007) Ignition of thermally Sensitive Explosives between a Contact Surface and a Shock. Physics of Fluids, 19:126102. [2] Short, M. and Quirk, J.J. (1997) On the non-linear stability and detonability limit of a detonation wave for a model three step chain-branching reaction, Journal of Fluid Mechanics, 339:89. [3] Sharpe, G.J., Maflahi, N. (2006) Homogeneous explosion and shock initiation for a three-step chainbranching reaction model, J.Fluid Mech., 566:163. [4] Clarke, J.F., Nikiforakis, N.N. (1999) Remarks on diffusionless combustion, Phil. Trans. R. Soc. Lond. A, 357:3605. [5] Melguizo-Gavilanes, J., Rezaeyan, N., Lopez-Aoyagi, M. and Bauwens, L. (2010) Simulation of shock-initiated ignition, Shock Waves, 20:467. [6] Bedard-Tremblay,L.,Melguizo-Gavilanes,J. and Bauwens, L. (2009) Detonation structure under chain-branching kinetics with small initiation rate, Proceedings of the Combustion Institute, 32:2339. [7] Melguizo-Gavilanes, J., Rezaeyan, N., Tian, M. and Bauwens, L. (2010) Shock-induced ignition with single step Arrhenius kinetics, International Journal of Hydrogen Energy, 36:2374.

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