HYDROGEN FLAMES IN TUBES: CRITICAL RUN-UP DISTANCES

Sergey DorofeevFM Global

2nd ICHS, San Sebastian, Spain, 2007

Motivation

• H2 releases and transport of H2-containing mixtures in confined geometries represent a significant safety problem Tubes / ducts

– Ventilation systems– Exhaust pipes– Production facilities

Tunnels• Promoting role of confinement for FA and pressure

build-up• Hydrogen: special attention because of high sensitivity

to FA

Hydrogen Safety Applications

Motivation

• Fast flames (supersonic relative to a fixed observer) represent a serious hazard to confining structures

• In cases of supersonic flames, DDT becomes possible further increase of pressure loads

• Possibility of FA to supersonic speeds limits implementation of mitigation techniques explosion suppression explosion venting

Hazard

4 8 12t, s

0.00.40.81.2

0.6 0.8 1.0t, s

02468

10

0.2 0.210102030

P, bar

t, s

Detonation

Fast Flame

Slow Flame

Motivation

• There are several limitations on the possibility of FA to supersonic flames and DDT mixture composition geometry scale … sufficiently large run-up distance

• Important to have reliable estimates for run-up distances

Limitations

Background

• Historically, run-up distances to DDT were addressed in most of studies Starting from Lafitte, Egerton, 1920th Shchelkin, 30th Followed by Jones, Soloukhin et al., Bollinger et. al.,

Nettleton, Campbell et al., Powel et al, Bartknecht, Fitt, Moen et al., Lee et al., Knystautas et al., Chan et al, Lindsted et al., Kuznetsov et al., Ciccarelli et al., Sorin et al….

• Run up distances were studied in Smooth tubes Tubes with obstacles

Run-up distances to DDT

Background

• Substantial experimental data accumulated Mixture composition Tube diameter Initial temperature and pressure

• Ambiguous data on the effect of tube diameter and pressure (detonation cell size) XDDT 15 – 40 D ?

XDDT independent on D ?

XDDT proportional to the cell size ?

• There is no universal and/or satisfactory model for the run-up distances

Run-up distances in smooth tubes

Background

• Effect of tube length Pre-compression or

pressure piling

• Effect of tube roughness Not always

characterized

• Difference in governing mechanisms Flame acceleration Onset of detonation

Ambiguity of run-up distances

V

X

Csp

DCJ

XS XDDT

Background

• Tube wall roughness and obstacles play an important role in FA and DDT Chapman and Wheeler (1926) used orifice plates to

promote FA Shchelkin proposed a wire coil helix inside the tube DDT in tubes with obstacles studied at McGill and by

many other teams

• XDDT and XS are often different in tubes with obstacles

Run-up distances in tubes with obstacles

Objectives

• Present a set of approximate models for evaluation of the run-up distances to supersonic flames Relatively smooth tubes Tubes with obstacles

• On the basis of these models, evaluate the critical run-up distances for FA in hydrogen mixtures Mixture composition Tube size BR and/or roughness Other parameters

Tubes with Obstacles

• Obstacles control FA: Strong increase

of flame surface Fast

development of highly turbulent flame

Flame evolution

105 ms

112

118.3

Shadow photos of Matsukov, et al.

Tubes with Obstacles

• Flame shape is given by obstacle field

• XS is the distance where the speed of the flame head approaches Csp

• XS D for given mixture, BR, and initial T, p

• Accuracy 25% over a representative range of data

Run-up distance Xs (Veser et al. 2002)

X

R

Turbulent flame brush

ST

U

BRb

BRa

c

S

R

X

sp

LS

1

1)1(10

Smooth Tubes

FA in smooth tubes

Shadow photos of Kuznetsov, et al.

Boundary layer

• Different from tubes with obstacles

• Boundary layer plays an important role

• Thickness of b.l. at flame positions increases during FA

Smooth Tubes

• Mass balance

• Burning velocity ST

• Boundary layer thickness

• Xs: V+ST = Csp

Model for Xs

V

ST + V

D

X d

Boundary layer

m

T DDS

DV

)1(4

2

6/12/1'

T

LL

T L

S

u

S

S

Kd

XC

ln1

Kd

D

CD

X S

ln

1

3/72

13/1

2)1(

m

L

sp

DS

c

= /D:

Two unknown parameters: m and

Smooth Tubes

Accuracy 25%

Correlation of model and experimental data

0

20

40

60

80

0 20 40 60 80XS/D experiment

XS/D

mo

de

lH2/Air D=0.174m

H2/Air D=0.52m

H2/O2/Ar D=0.174m

H2/O2/He D=0.174m

H2/O2 D=0.105m

H2/O2 D=0.015m

H2/O2 D=0.05m smooth

H2/O2 D=0.05m rough

C2H4/Air D=0.051m

model = test

BR: 0.002 – 0.1; SL: 0.6 – 11 m/s Csp: 790 -1890 m/s; D: 0.015 – 0.5 mXS/D: 10 - 80

Hydrogen and CH Fuels

• XS/D decreases with BR for given D

• FA is strongly promoted by obstructions

Run-up distances as a function of BR

D = 1 m

0

10

20

30

40

50

60

70

80

90

0.01 0.1 1

BR

XS/D

mo

de

lH2 BR<0.1

C2H4 BR<0.1

C3H8 BR<0.1

CH4 BR<0.1

H2 BR>0.3

C2H4 BR>0.3

C3H8 BR>0.3

CH4 BR>0.3

Obstructed tube

BR>0.3

Smooth tube

Hydrogen

• XS/D slightly decreases with D

• At sufficiently large d (so that BR>0.1) XS/D drops

Run-up distances versus tube roughness, d

H2/air

0

10

20

30

40

50

60

70

0.01 0.1 1 10 100 1000 10000

d, mm

XS/D

mo

de

lD=0.01m BR<0.1

D=0.1m BR<0.1

D=1m BR<0.1

D=10m BR<0.1

D=0.01m BR>0.3

D=0.1m BR>0.3

D=1m BR>0.3

D=10m BR>0.3

Hydrogen

• Smooth tubes: XS/D slightly decreases with D

• Obstructed tubes (BR>0.3): XS/D independent of D

Run-up distances for various D

H2/air

0

10

20

30

40

50

60

70

0.01 0.1 1

BR

XS/D

mo

de

lD=0.01m BR<0.1

D=0.1m BR<0.1

D=1m BR<0.1

D=10m BR<0.1

D=0.01m BR>0.3

D=0.1m BR>0.3

D=1m BR>0.3

D=10m BR>0.3

Hydrogen

• Decrease of the H2 from 30 to 12% leads to the increase of the run-up distances by a factor of 5

Effect of mixture composition

D = 0.1 m

0

50

100

150

200

250

300

0.01 0.1 1

BR

XS/D

mo

de

l"30% H2, BR<0.1"

20% H2, BR<0.1

15% H2, BR<0.1

12% H2, BR<0.1

30% H2, BR>0.3

20% H2, BR>0.3

15% H2, BR>0.3

12% H2, BR>0.3

Hydrogen

• Initial T and p affect SL, Csp, and • Changes are specific to particular mixture

Effect of T and P on run-up distances

D = 0.1 m

0

5

10

15

20

25

30

35

40

45

0.01 0.1 1

BR

XS/D

mo

de

l298 K, 1 bar, BR<0.1

353 K, 1 bar, BR<0.1

353 K, 2 bar, BR<0.1

498 K, 1 bar, BR<0.1

298 K, 1 bar, BR>0.3

353 K, 1 bar, BR>0.3

353 K, 2 bar, BR>0.3

498 K, 1 bar, BR>0.3

Concluding Remarks• A set of approximate models for the run-up

distances to supersonic flames in relatively smooth and obstructed tubes has been presented

These models attempt to capture physics relevant to FA in smooth and obstructed tubes

Show good agreement with the data in a wide range of mixture properties and tube wall roughness (or BR)

• The run-up distances depend significantly on:

mixture composition initial T and P tube size, and BR (or tube roughness)

• Each of these parameters should be taken into account in practical applications

Questions?

Smooth Tubes

• Different from tubes with obstacles

• Boundary layer plays an important role

• Thickness of b.l. at flame positions increases during FA

Mechanism of FA

Flame

Flame

Flame

V(x)

V(x)

V(x)

SW

SW

Flame(t1) Flame(t2) Flame(t3)

b. l.

b. l.

b. l.

(t1)b. l.

(t2)b. l.

(t3)

(t1) (t2)(t3)

(x)

Smooth Tubes

• Data with V(X) Kuznetsov et al.,

1999, 2003, 2005 Lindstedt and

Michels 1989

• BR: 0.002 – 0.1

• SL: 0.6 – 11 m/s

• Csp: 790 -1890 m/s

• D: 0.015 – 0.5 m

• XS/D: 10 - 80

Experimental data

0

10

20

30

40

50

60

70

80

90

0.001 0.01 0.1

BR

XS/D

exp

erim

en

t

H2/Air D=0.174m

H2/Air D=0.52m

H2/O2/Ar D=0.174m

H2/O2/He D=0.174m

H2/O2 D=0.105m

H2/O2 D=0.015m

H2/O2 D=0.05m smooth

H2/O2 D=0.05m rough

C2H4/Air D=0.051m

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10 12

SL, m/s

XS/D

exp

erim

en

t

H2/Air D=0.174m

H2/Air D=0.52m

H2/O2/Ar D=0.174m

H2/O2/He D=0.174m

H2/O2 D=0.105m

H2/O2 D=0.015m

H2/O2 D=0.05m smooth

H2/O2 D=0.05m rough

C2H4/Air D=0.051m

Fuels

• XS/D slightly decreases with D for given BR

• Large XS /D for C3H8 and CH4 – no data on XS and XDDT in smooth tubes

Run-up distances as a function of D

BR = 0.01

0

20

40

60

80

100

120

140

160

180

200

0.01 0.1 1 10

D, m

XS/D

mo

de

l

H2 BR<0.1

C2H4 BR<0.1

C3H8 BR<0.1

CH4 BR<0.1

Fuels

• Only XS /D-data with initial turbulence for propane and methane are available

• Correlate with effective SL: SLeff = 2.5SL

Run-up distances in “turbulent mixtures”

0

20

40

60

80

100

120

0 20 40 60 80 100 120XS/D experiment

XS/D

mo

de

lBartknecht, H2, C3H8, CH4, D=0.2-0.4 m

model = test