Challenges in Ambient Intelligence

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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
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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)

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DDT simulations
V.Gamezo et al., 31st Symposium International on
Combustion, Heidelberg 2006
2H
H
H/2
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DDT simulations
Source Gamezo et al.. 21st ICDERS, July 23-27,
2007, Poitiers
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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

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• 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
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• 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
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• 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
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Results BR 0.25
? L 0.08 m L 0.16 m L 0.32 m
0.6 FD 500 m/s FD 600 m/s
0.8 DDT FD 1000 m/s
1.0 DET 1900 m/s DDT
FD Fast Deflagration DDT Deflagration to
Detonation Transition DET - Detonation
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Results BR 0.5
? L 0.08 m L 0.16 m L 0.32 m
0.6 FD 650 m/s FD 600 m/s
0.8 FD 900 m/s DDT
1.0 DDT DET 2000 m/s
FD Fast Deflagration DDT Deflagration to
Detonation Transition DET - Detonation
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Results BR 0.75
? L 0.08 m L 0.16 m L 0.32 m
0.6 FD 550 m/s FD 500 m/s FD 500 m/s
0.8 FD 600 m/s FD 650 m/s FD 900 m/s
1.0 FD 700 m/s FD 700 m/s FD 950 m/s
FD Fast Deflagration DDT Deflagration to
Detonation Transition DET - Detonation
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• Results L 0.16 m

Average velocity of flame (open) and pressure
wave (solid) for L 160 mm
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• Results L 0.32 m

Average velocity of flame (open) and pressure
wave (solid) for L 320 mm
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• Results L 0.32 m, BR 0.25, ? 1

P1
P2
P3
P4
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• Results P3, L 0.16 m, BR 0.5

?0.8
?1.0
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• Results P4, L 0.16 m, BR 0.25

?0.6
?0.8
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Run-up distance for DDT
S.Dorofeev
In tubes at 0.1 MPa, H2-air
In our channel
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DDT limits
Characteristic dimension
Dorofeev criterion for DDT
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
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DDT limits in obstructed channels (H2-air)
w our studies L320mm w4 - h40mm, Ř-1.0 w5 -
h40mm, Ř-0.8 w7 - h20mm, Ř-1.0 L160mm w13 -
h40mm, Ř-1.0 w16 - h20mm, Ř-1.0 w17 - h20mm, Ř-0.8
S.Dorofeev
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• 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?)