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. Experimental study Channel: - length 2 m, width 0.11 m
heigth: H = 0.08 m 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. Experimental Diagnostics (pairs): - 4 piezoquartz pressure transducers
- 4 ion probes
Ignition:
- weak spark plug
Data acquisition:
- amplifier
- 8 cards (10MHz each)
- computer
H = 80 mm

8. Parameters of CJ Detonation
VCJ [m/s]
aCP [m/s]
 [mm]
0.6
1709
974 40
0.8
1866
1045 13
1.0
1971
1092 8
VCJ – detonation velocity
aCP – sound speed in combustion products
 - detonation cell size

9. Results – BR = 0.25  L = 0.08 m L = 0.16 m L = 0.32 m 0.6 FD 500 m/s
0.8
DDT
1000 m/s
1.0
DET
1900 m/s
FD – Fast Deflagration
DDT – Deflagration to Detonation Transition
DET - Detonation

10. Results – BR = 0.5  L = 0.08 m L = 0.16 m L = 0.32 m 0.6 FD 650 m/s
0.8
900 m/s
DDT
1.0
DET
2000 m/s
FD – Fast Deflagration
DDT – Deflagration to Detonation Transition
DET - Detonation

11. Results – BR = 0.75  L = 0.08 m L = 0.16 m L = 0.32 m 0.6 FD 550 m/s
0.8
600 m/s
650 m/s
900 m/s
1.0
700 m/s
950 m/s
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. Results – L = 0.32 m, BR = 0.25,  = 1 P1 P2 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:  7
Lch for the present study BR
L = 0.08 m
L = 0.16 m
L = 0.32 m
0.25
0.48 m
0.8 m
0.5
0.24 m
0.4 m
0.75
0.107 m
0.16 m
0.2 m  7
0.6
0.28 m
0.8
0.091 m
1.0
0.056 m

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. Conclusions
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?)