EXPLOSIONEXPLOSION HAZARD OF HAZARD OF HYDROGEN-AIR MIXTURES IN HYDROGEN-AIR MIXTURES IN

THE LARGE VOLUMESTHE LARGE VOLUMES

V.A. Petukhov, I.M. Naboko, and V.E. Fortov

Joint Institute for High Temperatures of Russian Academy of Sciences,

Institute for High Energy Densities

Izhorskaya 13/19, Moscow, 127512, Russia

petukhov@ihed.ras.ru

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Intention - investigation of non-stationary combustion of hydrogen-air mixtures that is important to the problems of safety

The conditions of occurrence and development of non-stationary combustion of hydrogen-air mixtures were studied:

in the tubes in the conic element in the spherical 12-m diameter chamber

On formation of non-stationary combustion in conic element the pressure in the cone top can reach 1000 atm

Investigations showed that in large closed volumes the non-stationary combustion of hydrogen-air mixtures can develop from a small energy source and pressure can exceed the Chapman-Jouguet pressure

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Total volume of experimental setup is 190 l.

Along the cone generatrix, 5 pressure sensors (1 – 5; M113A33 PCB) are located and one more (6; M109B11 PCB) is placed at the cone top.

Window-slot for high-speed photography is located along the generatrix.

The mixture was kept for about an hour. Its composition was monitored by gas analyzer IVA-IV (Chimavtomatika, Russia).

The mixture initiation was caused by blasting a RDX charge with the mass from 0.4 to 4.2 g. The charge was blasted by exploding copper wire 0.1mm in diameter.

Scheme of experimental conic setupScheme of experimental conic setup JIHT of RAS

600

1

2

3

4

5

6

x

80

400

680

543

Air + H2

Air

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a

Rubberenvelope

Metalcone

Initiationpoint

*

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Experimental conic setupExperimental conic setup

Rubber envelope

Window-slot

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Metal cone

The processes of combustion

investigated on the installation can be

conventionally divided into 3 types depending

on initiation energy and mixture

composition

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Front of primary combustion

Explosion luminescence in the cone top

timeInitiation of combustion

direction along

the axis of the cone

Streak photograph of combustion process in the Cone

Typical of the first regime results for Typical of the first regime results for combustion of stoichiometric Hcombustion of stoichiometric H22+air mixture +air mixture

initiated by 3.5 g RDXinitiated by 3.5 g RDX

The front of primary combustion comes to the

cone top after the explosion and

registration of the maximum pressure in the

cone top.

The front of secondary combustion interacts

with the front of primary combustion near the

cone top.

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P, atm t, s

625 560

1028 534

810 531

582 539

978 537

766 530

830 551

Maximum pressure at the cone top (P) and the time lapse

between moments of initiation and registration of maximum

pressure (t)

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Typical of the first regime results for combustion of Typical of the first regime results for combustion of stostoiichiometricchiometric H H22+air mixture +air mixture

initiated by 3.5 g RDXinitiated by 3.5 g RDX

The values of pressure in the cone top exceeding 1000 atmospheres result from the explosion caused by the cumulative

collapse of disturbances, which were spread before the front of the primary

combustion.

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Initiation of combustion

Front of primary combustion

Front of secondarycombustion

Streak photograph of combustion

Typical of the second regime results for Typical of the second regime results for combustion of Hcombustion of H22+air mixture in the Cone+air mixture in the Cone

With weaker initiation (under 2 g of RDX for stoichiometric H2+air

mixture ) as well as for poorer mixtures

the second regime is realized.

In this regime, ignition takes place in the cone top, and the secondary

flame front moves downwards. The

interaction with the primary front happens

at the cone base.

direction along

the axis of the cone

time

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Maximum pressure at the cone top (P) and the time lapse between the moment of initiation and the moment of registration of maximum

pressure (t)

Concen-tration of

Н2,

% vol.

RDX mass, g2.0 2.5 3.0 3.5 3.5

P, atm

t, s P, atm t, s P, atm t, s P, atm t, sP,

atmt, s

20 101.2 1500 166.7 1230 213.3 1150 173 1170

29 251 1112

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Typical of the second regime results for Typical of the second regime results for combustion of Hcombustion of H22+air mixture in the Cone+air mixture in the Cone

This regime is characterized by smaller values of pressure and slower process development as compared with the first regime

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Streak photograph of combustion

Typical of the third regime results for Typical of the third regime results for combustion of Hcombustion of H22+air mixture in the Cone +air mixture in the Cone

With even weaker initiation and poorer mixtures the third regime takes place. In this regime no ignition in the focusing area is

registered, no explosion takes place and no luminescence occurs in the cone top at the maximum pressures.

Initiation of combustion Front of primary combustion

direction along the axis of the cone

time

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Maximum pressure at the cone top (P) and the time lapse between the moment of initiation and the moment of registration of maximum

pressure (t)

Н2,

% vol.

RDX mass, g

1.0 1.5 2.0 2.5 3.0 3.5

P,atm

t, sP,

atmt, s

P, atm

t, sP,

atmt, s

P, atm

t, sP, atm

t, s

10 5.79 2384 13.7 2140 22.5 2040 30.86 1960 61.2 1768

15 26.7 1810 27.5 1700 37.7 1616 51.4 1576 44.28 1408

20 45.9 1590 39.6 1560

29 106.6 1472 124 1348

29 135 1645

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Typical of the third regime results for Typical of the third regime results for combustion of Hcombustion of H22+air mixture in the Cone +air mixture in the Cone

Maximum pressure values in cone top are 5-10 times higher than the pressure of focusing in inert gas at the same charge

of initiation

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1.5

0,076 0,153 0,229 0,305 0,381 0,458 0,534 0,61 0,686 0,763 above H2 , %mRDX , g

P , kbar

010

2030

40

04

812

16

0,40,81,21,6

3.0

1.0

2.0

Maximum pressure recorded in the cone top Maximum pressure recorded in the cone top in relation to the concentration of hydrogen in relation to the concentration of hydrogen

and mass of initiating RDX chargeand mass of initiating RDX charge

The results for all range of the investigated parameters were processed by the least-squares method

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Inside diameter – 12 m; wall thickness – 100 mm; weight – 470 t

Chamber is designed for explosion up to 1000 kg TNT and has been tested for static pressure of 150 atm

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Experimental schemeExperimental scheme

i4

i1 i2 i3

kII

kIII

kI

kIV

2300 2300

4100 4100

6000

1500

1500

450

upper manhole

kI-kIV – crusher membrane transducers

i1 – i4 – ionization sensors

lattice made from wood for turbulization of gas streams

bottom manhole

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all dimensions are in mm

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Inside view of explosive spherical camber before experiment

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29% H2 + 71% air Initial pressure – 1.4 atm

The mixture was held in the chamber during of 100 hours.

Measurements of mixture composition were carried out repeatedly with gas analyzer GT-201 (Gas Tech, Inc., USA).

The initiation of the reaction in the mixture was performed by exploding copper wire in the chamber centre; the discharged energy was about 6 J.

The goal of the experiment was to obtain the maximum possible values of pressure in large closed volumes at combustion of

hydrogen-air mixtures with weak initiation.

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Sensor number

S, m ti, msU(0-i)av. U(i-i+1)av. Uimax

m/s

1 2.0 56.5 35.4 70.8160

2 4.0 69.0 57.9 249.5143

3 5.9 83.0 72.3 34.34 1.7 47.0 36.1 72.0

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Results of measurement of primary flame front velocity Results of measurement of primary flame front velocity by ionizing sensorsby ionizing sensors

S - distance between the sensor and the point of ignitiont - time lapse between flame front arrival to the sensor and the moment of ignitionU(0-i)av. - average velocity of flame front propagation from the initiation point to the location of i-th sensorU(i-i+1)av. - average velocity of flame front propagation between sensors, Uimax - maximal calculated value of the flame front velocity in the vicinity of i-th sensor under the assumption that motion is uniformly accelerated

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Crusher membrane transducer

Measurement limit,

atm

Measured pressure,

atmNotes

kI 30 - 90 > 90Residual deformation of membrane

kII 100 - 300 190

kIII 30 - 90 > 90Residual deformation of membrane

kIV 100 - 300 180

Data ofData of crusher membrane transducerscrusher membrane transducers

Before the installation crusher transducers were calibrated by means of blasting various spherical charges TNT

and RDX. At calibrating the pressure was determined by calculation and by means of piezoelectric transducers.

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Explosive chamberExplosive chamber after experiment…after experiment…

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… … and nowand now

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The results presented are of interest for hydrogen safety.

The results obtained in the Cone are of interest as there is a cumulating device in almost each room (room angles).

It is demonstrated that in large closed volumes non-stationary combustion can develop from a source of small energy. The pressure can exceed the Chapman-Jouguet pressure.

In our opinion such a high pressure in wall area could be the result of explosion when intense shock waves were reflected from the wall.

When the mixture is initiated in the center of the chamber weak shock waves are formed. We suppose there are two mechanisms of the intensification of the waves: first – due to disturbances caused by the primary combustion front; second – due to shock waves passage through flame front.

In our experiment original shock waves could interact with the flame front three times. Estimations showed that for our conditions it was possible to appear such shock waves which reflected from the wall before the front of primary combustion reached the wall and were characterized by the intensity sufficient for initiation an explosion similar to that observed in the shock tube and cone.

ConclusionsConclusions