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

2nd International Conference on Hydrogen Safety, San Sebastian, 11-13 September 2007 A.Teodorczyk, WUT

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

A.Teodorczyk, P.Drobniak, A.DabkowskiWarsaw 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

H2HH/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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Channel:Channel:

- length 2 m,

- width 0.11 m

- heigth: H = 0.08 m

Experimental study

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

L Hh


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Experimental

DiagnosticsDiagnostics (pairs)):

- 4 piezoquartz pressure transducers

- 4 ion probes

Ignition:Ignition: - weak spark plug

Data acquisition:Data acquisition:- amplifier- 8 cards (10MHz each)- computer

H = 80 mmH = 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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DET - Detonation

L = 0.08 m L = 0.16 m L = 0.32 m

0.6 FD650 m/s

FD600 m/s

0.8 FD900 m/s

DDT

1.0 DDT DET2000 m/s


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DET - Detonation

L = 0.08 m L = 0.16 m L = 0.32 m

0.6 FD550 m/s

FD500 m/s

FD500 m/s

0.8 FD600 m/s

FD650 m/s

FD900 m/s

1.0 FD700 m/s

FD700 m/s

FD950 m/s


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

Results – L = 0.16 m

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

Ve

loci

ty (

m/s

)

1000 1200 1400 1600 1800D istance from the ignition point (m m )

P ressure transducer h=00m m


Ion probe h=20m m


Ion probe h=40m m


Ion probe h=60m m

L-160m m_fi=1.0


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

Results – L = 0.32 m

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

Ve

loci

ty

(m/s

)

1000 1200 1400 1600 1800D istance from the ignition point (m m )



Ion P robe h=20m m


Ion P robe h=40m m


Ion P robe h=60m m

L-320m m_fi=1.0


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Results – L = 0.32 m, BR = 0.25, = 1

0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re

(MP

a)0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (m s)

Pressure transducer

Ion probe

L320mm_h20mm_fi-1.0_exp5-01

0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re (

MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (m s)

Pressure transducer

Ion probe


0

1000

2000

3000

4000

5000V

olt

ag

e (

mV

)

0

2

4

6

8

Pre

ssu

re

(MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (m s)

Pressure transducer

Ion probe


0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re (

MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8Time (m s)

Pressure transducer

Ion probe


P1 P2

P3 P4


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Results – P3, L = 0.16 m, BR = 0.5

=0.8 =1.0

0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re (

MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (m s)

Pressure transducer

Ion probe


0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re (

MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (ms)

Pressure transducer

Ion probe



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Results – P4, L = 0.16 m, BR = 0.25

=0.6 =0.8

0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re (

MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (m s)

Pressure transducer

Ion probe


0

1000

2000

3000

4000

5000

Vo

lta

ge

(m

V)

0

2

4

6

8

Pre

ssu

re (

MP

a)

0 0.4 0.8 1.2 1.6 2 2.4 2.8

Time (ms)

Pressure transducer

Ion probe



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Run-up distance for DDT

S.Dorofeev

In tubes at 0.1 MPa, H2-air

600

800

1000

1200

1400

1600

1800

2000

2200

odle

głoś

ć od

pun

ktu

zapł

onu

[m

m]

0.2 0.4 0.6 0.8

BR

L=320m m _fi=1.0

L=320m m _fi=0.8

L=160m m _fi=1.0

L=160m m _fi=0.8

L=160m m _fi=0.6

In our channel


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DDT limits

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

7chL

Characteristic dimension:

1

1LLch

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HLL

H

hH

Lch for the present study

Dorofeev criterion for DDT:

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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)

S.Dorofeev

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


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• 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

Documents

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