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Fast Turbulent Deflagration and DDT of Hydrogen-Air Mixtures in Small Obstructed Channels

Fast Turbulent Deflagration and DDT of Hydrogen-Air Mixtures in Small Obstructed Channels A.Teodorczyk, P.Drobniak, A.Dabkowski Warsaw University of Technology, Poland. DDT simulations. V.Gamezo et al ., 31st Symposium International on Combustion, Heidelberg 2006

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Fast Turbulent Deflagration and DDT of Hydrogen-Air Mixtures in Small Obstructed Channels

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  1. Fast Turbulent Deflagration and DDT of Hydrogen-Air Mixtures in Small Obstructed Channels A.Teodorczyk, P.Drobniak, A.Dabkowski Warsaw University of Technology, Poland

  2. DDT simulations V.Gamezo et al., 31st Symposium International on Combustion, Heidelberg 2006 • stoichiometric hydrogen-air mixture at 0.1 MPa • Reactive Navier-Stokes equations with one-step Arrhenius kinetics • 2D channel with obstacles: length = 2m; height H = 1, 2, 4, 8 cm • Grid: 2 m (min)

  3. DDT simulations V.Gamezo et al., 31st Symposium International on Combustion, Heidelberg 2006 2H H H/2

  4. DDT simulations Source: Gamezo et al.. 21st ICDERS, July 23-27, 2007, Poitiers

  5. Objectives • Generate experimental data for the validation of CFD simulations • Determine flame propagation regimes and velocities as a function of: • blockage ratio • Obstacle spacing • Hydrogen-air mixture stoichiometry

  6. Channel: - length 2 m, • width 0.11 m • heigth: H = 0.08 m Experimental study L H h Obstacle heigth: h = 0.0, 0.02, 0.04, 0.06 m Blockage ratio: BR = 0.0, 0.25, 0.5, 0.75 Obstacle spacing: L = 0.08, 0.16, 0.32 m Stoichiometry:  = 0.6, 0.8, 1.0 Initial conditions: 0.1 MPa, 293 K

  7. Diagnostics (pairs): - 4 piezoquartz pressure transducers - 4 ion probes • Ignition: - weak spark plug • Data acquisition: - amplifier - 8 cards (10MHz each) - computer Experimental H = 80 mm

  8. Parameters of CJ Detonation VCJ – detonation velocity aCP – sound speed in combustion products  - detonation cell size

  9. Results – BR = 0.25 FD – Fast Deflagration DDT – Deflagration to Detonation Transition DET - Detonation

  10. Results – BR = 0.5 FD – Fast Deflagration DDT – Deflagration to Detonation Transition DET - Detonation

  11. Results – BR = 0.75 FD – Fast Deflagration DDT – Deflagration to Detonation Transition DET - Detonation

  12. Results – L = 0.16 m Average velocity of flame (open) and pressure wave (solid) for L = 160 mm

  13. Results – L = 0.32 m Average velocity of flame (open) and pressure wave (solid) for L = 320 mm

  14. P1 P2 Results – L = 0.32 m, BR = 0.25,  = 1 P3 P4

  15. Results – P3, L = 0.16 m, BR = 0.5 =0.8 =1.0

  16. Results – P4, L = 0.16 m, BR = 0.25 =0.6 =0.8

  17. Run-up distance for DDT S.Dorofeev In tubes at 0.1 MPa, H2-air In our channel

  18. DDT limits Characteristic dimension: Dorofeev criterion for DDT: Lch for the present study

  19. DDT limits in obstructed channels (H2-air) w – our studies L320mm w4 - h40mm, Ø-1.0 w5 - h40mm, Ø-0.8 w7 - h20mm, Ø-1.0 L160mm w13 - h40mm, Ø-1.0 w16 - h20mm, Ø-1.0 w17 - h20mm, Ø-0.8 S.Dorofeev

  20. Obstacles giving high channel blockage ratio are destructive for the flame propagation (large momentum losses) and regardless turbulizing effect they decrease hazard of DDT The importance of blockage ratio changes with the obstacle density. The higher blockage ratio the larger is optimum obstacle separation distance resulting in highest hazard for DDT. The obstacle density is less important for the lean mixtures ( = 0.6) for which no detonation was observed in the experiments. The predictions were found to be in general agreement with the correlation developed by Dorofeev et al. Advanced simulations show DDT very well qualitatively but still are not able to predict it quantitatively (transition distance ?, transition probability?) Conclusions

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