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


  • 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


  • 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


Parameters of CJ Detonation

VCJ – detonation velocity

aCP – sound speed in combustion products

 - detonation cell size


Results – BR = 0.25

FD – Fast Deflagration

DDT – Deflagration to Detonation Transition

DET - Detonation


Results – BR = 0.5

FD – Fast Deflagration

DDT – Deflagration to Detonation Transition

DET - Detonation


Results – BR = 0.75

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


P1

P2

Results – L = 0.32 m, BR = 0.25,  = 1

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:

Lch for the present study


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


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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