HYDROGEN FLAMES IN TUBES: CRITICAL RUN-UP DISTANCES Sergey Dorofeev FM Global 2 nd ICHS, San Sebastian, Spain, 2007
Dec 17, 2015
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
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