Paper 221 - THE STRUCTURE AND FLAME PROPAGATION

THE STRUCTURE AND FLAME PROPAGATION REGIMES
IN TURBULENT HYDROGEN JETS
A. Veser, G. Stern, N. Kotchourko, A. Friedrich
ProScience GmbH
M. Schwall, G. Fast, M. Kuznetsov*, W. Breitung
IKET, FZK
1
Background
icefuel®
integrated cable energy system for fuel and power
(R&D-Project)
• ICEFUEL – Energy System of the Future:
School
Shopping center
Houses
Office center
CO2-free primery energy sources:
Windmills
NPP
Information
Industry
LH2
Power
2
Accident scenarios
• Free release from Icefuel - cable
•
Effective leak
diameter 1-4 mm
Proposed operating conditions of the
Icefuel-cable: p = 15-30 bar, T = 20-33K
• Depending on the initial hydrogen
state we will have two phase flow, one
phase liquid flow or one phase gas flow
under iso-entropic hydrogen release
• Simplest case of high pressure
hydrogen release at temperature
T = 293K has to be investigated as a
reference scenario
3
• Diagram of state of para-H2
Objectives
•
In current work we consider an accident scenario in which the hydrogen
pipeline is broken and the released hydrogen jet is ignited
• In order to estimate the hazard potential we have to study the properties of
unburned and burned hydrogen jets released from a pressurized pipeline at an
ambient temperature to compare in further work the same properties for a
hydrogen jet at cryogenic temperatures 30K and 80K
4
High momentum jet characteristics
•
106
Temperature
300K
105
80K
104
Frden
Momentum
Dominated
300K
80K
35K
1000
•
100
Transient
10
Buoyant
Dominated
1
0.001
•
0.01
0.1
1
We can use Chen-Rodi correlations
for high momentum jet:
C(r)
u(r)
dr
x = x3
10
d (mm)
Axial concentration:
1/ 2
•
The buoyancy to inertia ratio is
expressed by densimetric Froude
number:
ρ 0 ⋅ u02
Fr =
(ρ ∞ − ρ 0 ) ⋅ g ⋅ d 0
d ef ⎛ ρ a ⎞
⎜
⎟
C ( x ) = A ⋅ C0 ⋅
⎜
x + x0 ⎝ ρ H 2 ⎟⎠
Axial velocity:
⎛ x + x0 ⎞
⎟⎟
u ( x) = u0 ⋅ B ⋅ ⎜⎜
d
⎝ 0 ⎠
x = x2
H2LFL
H2LFL
Radius r
x = x1
−1
x=0
5
Experimental set-up and variables
•
•
•
•
•
Pressure
Temperature
Nozzle diameter
Hydrogen mass flow rate
Ignition positions
5-60 bar
30-298 K
0.5, 1, 2 and 4 mm
0.3 – 6.5 gH2/s
0-2.5 m from the nozzle
• FZK experimental test site HYKA
Sampling probes
Nozzle
Spark-electrodes
BOS-Background
0
6
xign
x
2230mm
• Room dimensions:
5.5 x 8.5 x 3.4 m
(V = 160 m3)
Measurements
• Structure and characteristics of free hydrogen jet:
- Laser velocimetry - PIV (Particle Image Velocimetry - tracer: oil drops Ø2 μm
- H2 distribution - Background Oriented Schlieren (BOS) up to 1000 fr.p.s
- Hydrogen concentration (sampling probes)
Sampling probe array
single PIV image
Σ50 PIV image
BOS image
•Ignition and flame propagation regimes:
- Ignition position
- flame velocity (BOS up to 1000 fr.p.s)
- flame temperature (IR camera 25 fr.p.s)
- pressure
BOS image
7
IR image
Radial hydrogen concentration profile CH2(r)
Sampling probes - measurements
IF177, d=2 mm, m=3.3 g/s, T=290K
IF177, d=2 mm, m=3.3 g/s, T=290K
7
7
Hydrogen Concentration, C [mol.%]
Hydrogen Concentration, C [mol.%]
8
6
5
4
3
2
1
⎛ (r − μ ) 2 ⎞
⎟
exp ⎜ −
C H 2 (r ) =
⎜
σ 2π
2σ 2 ⎟⎠
⎝
A
0
-1
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
Radial Coordinate, r [m]
6
5
4
3
2
1
0
C H 2 (r ) =
z = 1.2 m
0.3
0.4
0.5
-1
-0.4
-0.3
-0.2
-0.1
⎛ (r − μ ) 2
exp ⎜ −
⎜
σ 2π
2σ 2
⎝
A
0
0.1
0.2
⎞
⎟
⎟
⎠
z = 1.4 m
0.3
0.4
Radial Coordinate, r [m]
H2-free jet, 290K, distances from the nozzle x = 1.2 and x =1.4 m
•
8
Gaussian profile of radial hydrogen concentration
0.5
Axial hydrogen concentration profile u(x)
H2- jet (30K, 80K, 298K)
Sampling probes – measurements
0.35
2mm T=298K
1mm T=298K
0.3
2mm T=80K
1mm T=80K
0.25
1mm T=65K
1/Vol%H2
1mm T=30K
0.2
0.15
0.1
0.05
0
0
200
400
600
800
1000
1200
(x/d)·(ρ a/ρ 0)1/2
• Hyperbolic decay of axial H2 concentration with distance
• Dependence can be easily linearized in consistency with Chen-Rodi correlation
• 30K data deviate from higher temperature data due to two-phase flow effect
9
Radial velocity profile u(r)
PIV - measurements
H2-free jet, 290K, different axial positions x/d0
•
•
10
Practically ideal Gaussian profile of radial flow velocity
Flow opening angle is about 22o - 25o
Axial velocity in free hydrogen jet
Mean axial flow velocity [m/s]
2D-PIV measurements of
flow velocity at 290 K
•
•
11
r ⎛u ⎞
v = ⎜⎜ ⎟⎟
⎝v⎠
Hyperbolic decay of axial
flow velocity with distance
−1
⎛ x − x0 ⎞
⎟⎟
ua = u0 B ⎜⎜
d
⎝ 0 ⎠
u0 = 1282 ms d 0 = 2 mm
B = 5.8
x0 = 38.4 mm
Hyperbolic decay of axial flow velocity with distance
Dependence can be easily linearized in consistency with Chen-Rodi correlation
Axial and radial fluctuations of flow velocity
2D-PIV measurements at 290 K
500
1
u [m/s]
Axial velocity u [m/s]
v'/v
0.8
300
0.6
200
0.4
100
0.2
0
Axial and radial velocity
fluctuations u'/u, v'/v
u'/u
400
0
0
200
400
600
800
1000
1200
1400
x/d0
•
•
12
The measured mean axial velocity fluctuations at the center line are remains
practically constant u rms / u ~30% for all measured positions along the jet axis up to
the distance of 25 d0
The averaged radial turbulence level v rms / v increases from 22% at 25d0 to 30% at
1400d0
Flame propagation regimes
Fast flame
30K experiments
d=0.5 mm
P=30 bar
Slow flame
x = 1. 6 m
•
x = 1.5 m
13
Distance :
– no ignition
– slow flames and local quenching
– fast flame acceleration
Flame propagation regimes in hydrogen jet
•
Flame propagation regimes in H2-jet:
– no ignition
– slow flames and local quenching
– fast flame acceleration
xign = 800 mm
xign = 900 mm
H2-jet (5 bar, 290K),
Ønozzle = 4 mm,
tinj=3s (3.5 g/s),
framing time step = 300ms
0.4
1 mm, T=298K
2 mm, T=298K
1/Vol% H 2
no ignition
1 mm, T=80K
0.3
2 mm, T=80K
4%
0.2
slow
0.1
11%
30%
fast
0
0
200
400
600
800
1/2
(x/d0)·(ρ u/ρ a)
Flame
Jet flow
14
1000
1200
1400
Flame propagation regimes in hydrogen jet
Phase diagram of turbulent flame propagation regimes
10000
•
DNS
Well-stirred
Reactor
Re=10000
1000
Re=100
Quenching
11%H2
•
u'/SL
100
Distributed
Reaction
Zone
10
Da=1
Ka=1
•
Flamelet
Regime
1
Re=1
Laminar flamelet regimes (Ka<1, Da >1)
Typical for highly reactive laminar or quasilaminar flames (t < tK). Thin flames zone.
Maximum what turbulence can achieve is to
wrinkle the flame
Distributed reaction zone (Ka>1, Da >1)
Typical for thick flames. Small eddies already
can penetrate into the flame brush to make it
thicker (tT > t > tK). Wrinkled or corrugates
flames. Above the quenching line local
quenching can occur.
Well stirred reactor zone (Ka>1, Da <1)
Turbulence destroy flame brush (tT < t ).
Global quenching can occur.
0.1
0.1
1
10
lT/δ L
100
1000
10000
Critical point characteristics (CH2 = 11%):
•
•
•
•
15
Turbulent pulsations and flow velocity:
Laminar velocity and flame thickness:
Integral scale (large eddies size):
Dimensionless turbulent pulsations :
u’/u = 25%;
u = 57 m/s
SL= 0.2 m/s,
δL = 0.23 mm
lT >= 5 cm (conservative) Î lT /δT~ 200
Î u’/SL = 70
Conclusions
• Horizontal quasi-stationary high-momentum hydrogen jets with
different temperatures, nozzle diameters and different mass flow
rates in the range from 0.3 to 6.5 g/s have been investigated
• An optical PIV method and sampling probe techniques combined
with a gas analyzer have been used for jet structure investigation.
It was shown that the experimental data are in good consistency
with Chen - Rodi scale correlation
• Combustion experiments with variable ignition points showed that
stable flame with maximum flame velocity can only occur if the
hydrogen concentration at the ignition point exceeds 11% of
hydrogen. In this case the flame propagates up- and downstream
the jet, whereas in case of less than 11% of hydrogen the flame
propagates only downstream or quenches
• The data on hydrogen jet combustion are in good consistency with
our previously proposed expansion ratio- or σ-criterion as a flame
acceleration potential
16
Acknowledgements
icefuel®
integrated cable energy system for fuel and power
(R&D-Project)
17