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 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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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?)