DISPERSION TESTS ON CONCENTRATION AND ITS FLUCTUATIONS FOR 40MPa PRESSURIZED HYDROGEN A. Kouchi, K. Okabayashi, K. Takeno, K. Chitose Mitsubishi Heavy

DISPERSION TESTS ON CONCENTRATION AND ITS FLUCTUATIONS FOR 40MPa PRESSURIZED HYDROGEN

A. Kouchi, K. Okabayashi, K. Takeno, K. Chitose

Mitsubishi Heavy Industries, Ltd.

2nd International Conference on Hydrogen Safety, September 12, 2007, San Sebastian, Spain

BackgroundHydrogen refueling stations which are being planned at the present will store high-pressure hydrogen gas at 40 MPa.

The acquisition of basic data on the influence of high-pressure hydrogen gas on the surroundings has become an urgent task.

We focused on a typical leakage scenario, i.e., leakage from a pinhole occurring in equipment, resulting in continuous leakage at a constant mass flow rate (steady leakage)

Purposes of this Study and Basic Methodology To comprehend the basic behavior of the dispersion of high-

pressure hydrogen gas where there is steady leakage from a pinhole.

Field dispersion experiments :Data sets of time-averaged concentrations were obtained.

However, to investigate the safety of flammable gas dispersion, time-averaged concentrations are insufficient.

Because concentration fluctuates due to turbulence.

To study the relationships among the concentration fluctuation, the occurrence probability of flammable concentration and the features of the flame propagation.

Dispersion and Spark-Ignition Experiments:

-Measurements of instantaneous concentration fluctuations

-Spark-ignitions were also applied at the same point simultaneously

-Characteristics of the flame propagation were analyzed

Dispersion Experiments for Time-averaged Concentrations

Experimental Apparatus and Test Field

(in Akita pref.) Tashiro experimental facility

放出口

Concentration Measurement　 Poles

Release Nozzle-High-pressure Hydrogen gas was released horizontally. -1m above the ground.

Nozzle


Release conditions

Concentration Measurement

Stagnation Pressure P0= 40 MPa, Nozzle Diameter D = 0.25, 0.5, 1.0 , 2.0 mm

P0= 20 MPa , D = 2.0 mm

10

0 10 20 30 50

-5

0

5

10 20 30 50

X: Distance from the nozzle

[m]

5

Z: H

eigh

t fr

om t

he

grou

nd [m

] L

ater

al d

ista

nce

[m

]

X: Distance from the nozzle [m]Lat

eral

Dis

tan

ce

[m]

Hei

gh

t [

m]

10

10

20 30 50

5030

Time-averaged concentration was measured at each point


Results(1) A typical example of concentration contour [ P0=40MPa, D=2.0mm] Unit[％]

×

5

30 X[m] 20 0 10

4 2

1

10

Z[m

]

Nozzle

The gas plume: Almost horizontal near the nozzle -The momentum effect is more dominant than the buoyancy effect in a high concentration area

Using an analogy from the turbulent jet characteristics of incompressible jet flow

Time-averaged concentration along the axis of the plume was plotted against X/θ: - θ : Equivalent release diameter

a

D

0 ρa: Density of ambient air

ρ0: Density of hydrogen at nozzle throat

0.1

1

10

100

10 100 1000 10000 100000

Nondimentional distance from nozzle X/ θ

Con

cent

ratio

n C

m (

)％

φ 0.25mm 40MPa、φ 0.5mm 40MPa、φ 1.0mm 40MPa、φ 2.0mm 40MPa、φ 2.0mm 20MPa、Formula(2): a1=6000


Results(2) Time-averaged concentration along the axis of the plume

Far from the release point : -Scattering is relatively larger due to the fluctuation of meteorological conditions and smaller momentum of hydrogen jet.

At a short distance: -Scattering becomes smaller. -The plotted points are almost in alignment.

- Concentration along the axis of the dispersion plume can be expressed as a simple formula, where a1=6000.

-This formula will enables us to estimate the axial concentration easily in case the release diameter and initial pressure are given.

1

1

X

aCm

Dispersion and Spark-Ignition Experiments for Concentration Fluctuations

-To study the relationships among the concentration fluctuation, the occurrence probability of flammable concentration and the features of the flame propagation.

Experimental Apparatus and the Method of the ExperimentsNozzle Flame size

Hydrogen supply(40MPa)

Including 1.5% Methane

Spark controller

Methane concentration sensor

Spark plugSampling for concentration measurement

Anemometer High speed camera Pressure sensor

-Hydrogen release: horizontally as pinhole leakage.-Methane gas was mixed into hydrogen gas to a concentration of 1.5vol% as a tracer gas, for the purpose of measuring concentration fluctuation using a fast response flame ionization detector.

-Electric spark-ignition also applied simultaneously.-The phenomena of flame generation and propagation were recorded with a high speed video camera.

Sampling tube for concentration measurement

Ignition plug

Dispersion and Spark-Ignition Experiments for Concentration FluctuationsExperimental Apparatus and the Method of the Experiments

- Concentration : Fast response FID (HFR400) ,Sampling rate : 200Hz.- Electric spark-ignition :10 Hz, the electrode gap:1.5 mm, spark energy :120 mJ - High speed video camera : 500 flames/sec. An UV band-pass filter (313 ± 7 nm) was attached for taking images of the hydrogen flame ( a spectrum peak : around 310 nm)

- Pressure sensor : Ambient pressure change due to ignition 2.5m away from the ignition point.

Nozzle

High speed camera Pressure sensor

Release Condition

Stagnation Pressure : P0 40MPa

Nozzle Diameter : D 0.2mm

Measurements Points

Distance from the nozzle: X0.15m 、 0.3m 、 0.35m 、 0.4m 、 0.45m 、 0.7m 、 0.8m 、 0.9m 、 1.0m 、 1.5m 、 2.5m

Experimental Conditions



Data analysis method (1) Concentration time-history data analysis

Concentration time-history of Hydrogen

0

2

4

6

8

10

12

14

30.0 31.0 32.0 33.0 34.0 35.0

Time [sec]

Hyg

roge

n co

ncen

trat

ion

[%]

Time-averaged concentration: Cm

ex) Cm = 4.1%

Example: X=0.9m

Probability density function of concentration: PDF

0.0

1.0

2.0

3.0

4.0

5.0

0 5 10 15 20Concentration [%]

Pro

babi

lity

of o

ccur

renc

e[%]

Concentration [%]

Pro

ba

bili

ty o

f o

ccu

rre

nce

[%

]

Cm=4.1%

Occurrence probability of flammable concentration: PC

ex) PC= 57%

300mm

Ignition Spark

Hydrogen Flame

Dispersion and Spark-Ignition Experiments for Concentration FluctuationsData analysis method (2) Image data analysis

Each image from the high speed video camera

Example: X=0.3m

-Occurrence probability of hydrogen flame: PF

(= number of times flame was generated/ number of times sparks were generated)- Flame size : LF (Maximum size during one spark)- Flame propagation distance : LD

Flame size: LF

Flame propagation distance: LDElectrode for spark

Dispersion and Spark-Ignition Experiments for Concentration FluctuationsResults

Time-mean concentration

0

5

10

15

20

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Distance from the nozzleX[m]

Tim

e-av

erag

ed c

once

ntra

tion

Cm

[%]

Distance from the nozzle [m]

Tim

e-m

ea

n c

on

cen

tra

tion

Cm[%

]

Relationship between Cm and PC

0

20

40

60

80

100

120

0 4 8 12 16Time- averaged concentration Cm[%]

Pc[

%]

Time-averaged Concentration Cm [%]

Occ

urre

nce

pro

babi

lity

of

flam

mab

le c

once

ntra

tion

PC[%

]

(1) Concentration time-history data analysis

-Cm is larger than about 7% Pc is near 100%. -The concentration is always higher than LFL, i.e. 4%.

-As Cm becomes smaller, Pc decreases and almost zero at around Cm =2%. -This implies that there is no possibility of ignition in an area where time-averaged concentration is lower than 2% even if concentration fluctuation is considered.

Dispersion and Spark-Ignition Experiments for Concentration FluctuationsResults (2) Image data analysis

0

100

200

300

400

500

0 2 4 6 8 10 12 14 16Cm（％）

LF [m

m]

Mean valueMaximum value

3系列

Time-averaged Concentration Cm [%]

Fla

me

siz

e L F

[mm

]

100mm100mm

Spark (not hydrogen flame)

X=0.9m (Cm=4.1%, PC=57%)

100mm

X=0.6m (Cm=5.4%, PC=88%) X=0.3m (Cm=8.7%, PC=99.8%)

X=0.15m Cm=15.2%, PC=100%)

100mmSteady jet flame

-Cm is 4.1% Hydrogen flame cannot be recognized. -As Cm larger, LF becomes larger.-X=0.15m, Cm is 15.2%, the flame was generated at the first spark and it grew to a steady jet flame.

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16Cm[%]

PF [%]

Dispersion and Spark-Ignition Experiments for Concentration FluctuationsResults (2) Image data analysis

100mm100mm

Spark (not hydrogen flame)

X=0.9m (Cm=4.1%, PC=57%)

100mm

X=0.6m (Cm=5.4%, PC=88%) X=0.3m (Cm=8.7%, PC=99.8%)

Occ

urre

nce

pro

babi

lity

of

hydr

ogen

fla

me

PF [

%]

-As Cm decreases, PF become smaller, approaching zero around at Cm=5%.

-This phenomenon is consistent with the fact that Pc is almost zero when Cm is around 2%, i.e., when there is no possibility of ignition.

(3) Pressure Measurement

-Ambient pressure change caused by flame generation an undetectable level ( i.e. less than 100 Pa)

Conclusions Time-averaged hydrogen concentration can be expressed by a simple

formula. This formula will enable us to estimate axial concentration at each distance easily. 1

1

X

aCm

The occurrence probability of flammable concentration Pc decreases with decrease in the time-averaged concentration and becomes almost zero and no significant flame propagation occurs, where Cm is around 2% or less.

Thus, there is a clear correlation between the time-mean concentration, the occurrence probability of flammable concentration, flame length and occurrence probability of hydrogen flame.

However, these results were derived from experimental data under regulated conditions. Further data acquisition under various conditions such as larger leakage diameter or where there are obstacles is to be expected and this will be our future task.

Documents

DISPERSION TESTS ON CONCENTRATION AND ITS FLUCTUATIONS FOR 40MPa PRESSURIZED HYDROGEN A. Kouchi, K. Okabayashi, K. Takeno, K. Chitose Mitsubishi Heavy