Explosions in Methane O2 N2 Mixtures in Vessels

H.-P. Schildberg, 41st UKELG meeting, 13 May 2008, Shell Technology Centre Thornton1

Course of explosions in Propene/O2/N2 and Methane/O2/N2mixtures in vessels of 20 l to 2500 l

and load on the walls

Dr. Hans-Peter SchildbergBASF-AG

GCT/S - L511D-67056 Ludwigshafen

Email: [email protected]: +49 621 60-56049

H.-P. Schildberg, 41st UKELG meeting, 13 May 2008, Shell Technology Centre Thornton 2

Outline of talk

Explosion characteristics

Introduction

Course of explosion in 20 l sphere

Comparison: detonative regimesin 20 l vessels ↔ 100, 500, 2500 l vessels

Predetonation distances of Propene/O2 in tubes

Pressure load Pdet on the wall of the vessel- quantification of Pdet for four scenarios occuring in a pipe (no precompression)- quantification of Pdet for four scenarios occuring in a pipe (with precompression)- quantification of Pdet for Propene/O2/N2 in vessel at Pinitial = 5 bar abs, Tinitial = 20 °C

Did ignition source directly trigger a spherical detonation?


Information available in literature on explosive gas mixtures of type combustible/O2/N2

Explosion characteristics(explosion limits, pex, (dp/dt)ex)

Course of explosion(deflagrative, detonative, heat explosion)

=> Much work needed to better understand combustible/air/O2 mixtures

- -- -pex, (dp/dt)ex

- -oexplosion limitscombustible / air /O2

-+pex, (dp/dt)ex

o+ +explosion limitscombustible / air /N2

pinitial > 1 barapinitial ≤ 1 bara

- -- -vessel (L/D ≅ 1)

- --pipe (L/D > 100)combustible / air /O2

- -+vessel (L/D ≅ 1)

++ +pipe (L/D > 100)combustible / air /N2

pinitial > 1 barapinitial ≤ 1 bara 0 10 20 30 40 50 60 70 80 90 100combustible [vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2

[vol.-%]

0

10

20

30

40

50

60

70

80

90

100

N 2[v

ol.-%

]

combustible/air mixtures

0 10 20 30 40 50 60 70 80 90 100combustible [vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2

[vol.-%]

0

10

20

30

40

50

60

70

80

90

100

N 2[v

ol.-%

]

combustible/air mixtures

explosive range ofcombustible/air/N2

explosive range ofcombustible/air/O2


Motivation for this work

Trend in partial oxidation reactions:

Advantages:- increase of yield in space and time

- lower operating pressures

Critical Issue when dealing with combustible/air/O2-mixtures: Process Safety

- course of explosion (deflagration, detonation)

- explosion characteristics- vessel-like geometry

- bubble column geometry (explosive gaseous bubbles dispersed in liquid)

- course of explosion (deflagration, detonation)

- mechanisms of flame propagation

- replacing air or diluted air as oxidant by oxygen enriched air or by pure oxygen

Focus of this work


Gaseous mixtures investigated

Propene / O2 / N2,

Methane / O2 / N2

Cyclohexane / NO2

Cyclohexane / NO

Cyclohexane / N2O

Hydrogen / O2

very detailed exp. investigations

only for one value of Pinitial and Tinitial



Introduction







Experimental setup

20 l sphere, Pmax=600 bar, Tmax=500°CTest vessel:20 l sphere

Ignition source:exploding wire according to EN1839,Bomb method, section 4.2.3.3.3(arc discharge, ca. 200 A over ca. 3 ms)

Ignition energy:ca. 20 J

Mixture preparation:partial pressure method, ideal gas characteristics assumed


References for complete documentation of explosion characteristics

H.P. Schildberg in deliverables no. 8 and no. 13 of EU-Research Project SAFEKINEX, Contract No. EVG1-CT-2002-00072; download possible from www.safekinex.org

“Explosion characteristics of Propene/O2/N2 at 1, 5, 10 and 30 bar abs, 25 °C and 200 °C”,Hans-Peter Schildberg in „Process Safety and Industrial Explosion Protection“,editor: ESMG – European Safety Management Group e. V. , Hamm, Germany (2005), ISBN 3-9807567-4-2 (proceedings of the International ESMG Symposium 2005 in Nürnberg, Germany, 32 pages )

“Determination of the Explosion Behaviour of Methane and Propene in Air or Oxygen at Standard and Elevated Conditions”, A.A. Pekalski, H.-P. Schildberg, P.S.D. Smallegange, S.M. Lemkowitz, J.F. Zevenbergen, M. Braithwaite, H.J. Pasman, 11th International Symposium Loss Prevention and Safety Promotion in the Process Industries (2004), Praha Congress Centre 31st May-3rd June 2004;Thematic Section B, page 2118-2138 (ISBN 80-02-01574-6)

“Determination of the Explosion Behaviour of Methane and Propene in Air or Oxygen at Standard and Elevated Conditions”, A.A. Pekalski, H.-P. Schildberg, P.S.D. Smallegange, S.M. Lemkowitz, J.F. Zevenbergen, M. Braithwaite, H.J. Pasman, Process Safety and Environmental Protection, Volume 83, issue B5, 421-429 (2005)



Introduction







Questions to be raised when considering explosions of combustible/air/O2 mixtures in vessel-like geometry

What compositions will undergo a transition from Deflagration to Detonation (DDT) after ignition with a thermal ignition source?

What is the largest conceivable pressure load on the vessel wall?

Will combustible/air mixtures remain deflagrative for higher values of Tinitial and Pinitial?

How about the „obscure“ effects reported mostly only in non-publiccommunication?

(Vessels believed to be explosion pressure proof did sometimesrupture, but when repeating the experiment at same initial pressurewith even the worst case mixture (i.e. what one believed to be worstcase), a mechanically identical vessel did withstand the load).

How does the volume of the vessel affect the detonative range?


Literature data on deflagrative and potentially detonativeexplosion regime of n-Butane/O2/N2 at 1 bar abs, 20 °C

0 10 20 30 40 50 60 70 80 90 100n-Butane [Vol.-%]

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

binary mixture n-Butane/air

stoich

iomet

ric ra

tio n-

Buta

ne : O

2 = 1

: 6.5

0

range of

deflagrative explosionrange

of m

ixture

s, whe

re

trans

ition f

rom de

flagra

tive t

o

deton

ative

explo

sion i

s pos

sible

Characteristic values of the explosive range [1]:

Lower explosion limit in air: 1.4 vol.-% Upper explosion limit in air: 9.4 vol.-%

Lower detonation limit in air: 1.98 vol.-%Upper detonation limit in air: 6.18 vol.-%

Lower detonation limit in O2: 2.05 vol.-%Upper detonation limit in O2: 38 vol.-%

Upper explosion limit in O2: 51 vol.-% Lower explosion limit in O2: 1.4 vol.-%

Characteristic values of the potentially detonative range [2,3]:

Limiting oxygen concentration: 9.4 vol.-%

[1] E. Brandes and W. Möller, Sicherheitstechnische Kenngrößen - Band 1: Brennbare Flüssigkeiten und Gase, Wirtschaftsverlag NW, Bremerhaven (2003), ISBN: 3-89701-745-8; UEL in O2 is an estimate, basis is measured value of 56 Vol-% at 200 °C, ZET-report no. 197.0390.3N

[3] M. A. Nettleton in Gaseous Detonations, p. 76, Chapman and Hall Ltd, New York (1987)

[2] M. A. Nettleton, Fire Prev. Sci. and Tech. No 23, p.29 (1980)


What does „potentially detonative regime“ mean?

If a mixture lies outside the potentially detonative regime, an explosionwill under all circumstances (e.g. type of ignition source, geometry) only bedeflagrative

If the mixture lies inside the potentially detonative regime and a thermal*ignition source triggers an explosion, the flame front will initially propagateas deflagration and the transition to detonation (DDT) will not necessarilyoccur!

There are further conditions that have to be fullfilled to enable the DDT (e. g. geometry of the containment must support flame acceleration). However, in practical applications it is mostly hard to assess to which degreethese conditions are satisfied. There are absolutely no simulation tools (e.g. reactive CFD codes) availablewhich could predict the DDT in vessels at least to some rudimentary extent.

*: in process plants almost all ignition sources are thermal. The initial stage of the explosion theycan trigger is always deflagrative

If the mixture lies inside the potentially detonative regime and a detonative ignition source triggers an explosion, the flame front will propagate as detonation right from the beginning


Literature data on deflagrative and potentially detonativeexplosion regime of Propen/O2/N2 at 1 bar abs, 20 °C

Characteristic values of the explosive range [1,2]:

Lower explosion limit in air: 2 vol.-% Upper explosion limit in air: 11 vol.-%


Lower detonation limit in O2: 2.50 vol.-%Upper detonation limit in O2: 50 vol.-%

Upper explosion limit in O2: 58 vol.-% Lower explosion limit in O2: 2 vol.-%

Characteristic values of the potentially detonative range [3]:


[1] E. Brandes and W. Möller, Sicherheitstechnische Kenngrößen - Band 1: Brennbare Flüssigkeiten und Gase, Wirtschaftsverlag NW, Bremerhaven (2003), ISBN: 3-89701-745-8;


[2] H.P. Schildberg in „Process Safety and Industrial Explosion Protection“, editor: ESMG European Safety Management Group e. V. , Hamm, Germany (2005), ISBN 3-9807567-4-2 (proceedings of the International ESMG Symposium 2005 in Nürnberg, Germany, 32 pages )

0 10 20 30 40 50 60 70 80 90 100Propene [Vol.-%]

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

binary mixture Propene/air

stoich

iometr

ic ra

tio P

rope

ne : O

2 = 1

: 4.5

0

range of

deflagrative explosion

range o

f mixt

ures,

where

transiti

on fro

m deflag

rative

to

detona

tive e

xplosio

n is po

ssible


Literature data on deflagrative and potentially detonativeexplosion regime of H2/O2/N2 at 1 bar abs, 20 °C

0 10 20 30 40 50 60 70 80 90 100H2 [Vol.-%]

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

binary mixture H2/air

stoichiometric ratio H2:O2 = 2:1

0

ra

nge

of

defla

grat

ive e

xplo

sion

range of mixtures, wheretransition from deflagrative to

detonative explosion is possible

Characteristic values of the explosive range [1,2]:

Lower explosion limit in air: 4 vol.-% Upper explosion limit in air: 77 vol.-%


Lower detonation limit in O2: 15 vol.-%Upper detonation limit in O2: 90 vol.-%

Upper explosion limit in O2: 95.2 vol.-% Lower explosion limit in O2: 4 vol.-%

Characteristic values of the potentially detonative range [3]:


[1] E. Brandes and W. Möller, Sicherheitstechnische Kenngrößen - Band 1: Brennbare Flüssigkeiten und Gase, Wirtschaftsverlag NW, Bremerhaven (2003), ISBN: 3-89701-745-8


[2] V. Schröder in „Process Safety and Industrial Explosion Protection“, editor: ESMG European Safety Management Group e. V. , Hamm, Germany (2005), ISBN 3-9807567-4-2 (proceedings of the International ESMG Symposium 2005 in Nürnberg, Germany)


Experimental setup to determine the potentiallydetonative range of explosive gas mixtures

location of thermal ignition source forbooster mixture

Signals of pressure and/or flame sensors give evidence whether a stable detonation could be

triggered in the mixture

„Booster-mixture“, Acetylene/O2, stoichiometric with respect to formation of CO and H2O. It transits to detonation after a few millimeters and acts upon the mixture to be tested with a stronger detonation front than the one that occurs in the mixture whenit undergoes a detontive explosion

mixture to be tested for potential detonability (i.e. ability to propagate a detonation which was onceinitiated either by an external source or by an initially deflagrative explosion in the mixture to be tested, which succeeded in running up to a detonation)

thin membrane or nothing(after injecting the mixtureto be tested the boostermixture is injected close to the ignition source and propagates almost as plugflow into the pipe)

Note:Pipe must be long enough for to allow that the initial state of the overdriven detonation canpass over to a stable final state, which can be either a stable detonation or a deflagration in the mixture to be tested.

ca. 15*pipe diameters


Different explosion regimes (deflagration, heat explosion, detonation) found for Propene/O2/N2 in a 20 l sphere at 5 bar abs, 25 °C

yellow range:possibly heat explosion

0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

range of deflagrative explosion, 5 bar abs, 25 °C

range of detonative

explosion

stoich

iometric C 3H 6 +

1.5 O 2 -> 3 CO + 3 H 2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO + 3 H 2O

stoich

iometr

ic C 3H

6 +

4.5 O

2 ->

3 CO 2 +

3 H 2O

soot is formed here

(43 vol.-% up to 69 vol.-%

)

propene/air-mixtures


Different explosion regimes (deflagration, heat explosion, detonation) of Propene/O2/N2 in a 20 l sphere at Pinitial = 1, 5 and 10 bar abs, 25 °C

0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]




range of detonative

explosion

stoichiometric

C 3H 6 + 1.5 O 2 -

> 3 CO + 3 H 2sto

ichiom

etric

C 3H6 +

3 O 2 -

> 3 CO + 3

H 2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 ->

3 CO 2 +

3 H 2O


0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoichiometric

C 3H 6 + 1.5 O 2 -

> 3 CO + 3 H 2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO + 3 H 2O

stoich

iometr

ic C 3H

6 +

4.5 O 2

-> 3

CO 2 + 3

H 2O

soot is formed here

(43 vol.-% up to 69 vol.-%

)



0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

30

40

50

60

70

80

90

100

Propene C3H6 [Vol.-%]

N 2 [V

ol.-%

]

O2 [Vol.-%

]stoich

iometr

ic ra

tio P

ropen

e : O 2

= 1 :

4.5



range of detonative

explosion

(boundary at propene

conc. > 10 vol.-% only

estimated)

1 bar abs 5 bar abs

10 bar abs 30 bar abs

(Heat explosion range and detonative range were notdetermined. It might bethat the detonative rangeeven extends down to theair line)


Different explosion regimes (deflagration, heat explosion, detonation) of Propene/O2/N2 in a 20 l sphere at 1, 5 and 10 bar abs, 200 °C

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100


N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40

stoichiometric C 3H 6 +

1.5 O 2 -> 3 CO + 3 H 2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO + 3 H 2O

stoich

iometr

ic C 3

H 6 + 4.

5 O2 -

> 3 C

O 2 +

3 H 2

O


r

ange of

deflagrative explosion,

5 bar abs, 200 °C

range of detonative explosion


0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

30

40

100


N 2 [V

ol.-%

] O2 [Vol.-%

]stoich

iometric C 3H 6 +

1.5 O 2 -> 3 CO + 3 H 2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO + 3 H 2O

stoich

iometr

ic C 3H

6 +

4.5 O 2

-> 3

CO 2 + 3

H 2O


range of detonative

explosion

soot is formed here

(41 vol.-% up to 75 vol.-%

)


90

50

60

70

80

20

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

30

40

100


N 2 [V

ol.-%

] O2 [Vol.-%

]

stoichiometric

C 3H 6 + 1.5 O2 -

> 3 CO + 3 H 2

stoich

iometr

ic C 3

H 6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3

H 6 + 4.

5 O2 -

> 3 C

O 2 +

3 H2O



90

50

60

70

80

20

range of detonative

explosion

yellow range:possibly heat explosion (Heat explosion range and

detonative range were notdetermined. It might bethat the detonative rangeeven extends down to theair line)

1 bar abs 5 bar abs

10 bar abs 30 bar abs


Different explosion regimes (deflagration, heat explosion, detonation) of Methane/O2/N2 in a 20 l sphere at 1 and 5 bar abs, 25 °C and 200 °C

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100

Methane CH4 [Vol.-%]

N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40

methane/air-mixtures

range of


1 bar abs, 25 °Csto

ichiom

etric CH 4

+ 2O2 -

> CO 2 + 2H

2O

stoich

iometric CH4 + 1.5O 2 -

> CO + 2H2O

stoichiometric CH4 + 0.5O2 -> CO + 2H2

soot formation starts

at 55 vol.-% CH

4

mixture reacts sometimesdetonative and sometimesas heat explosion

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100


N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40


stoich

iometric

CH4 + 2O

2 -> CO2 +

2H2O

stoich

iometric CH4 + 1.5O2 -

> CO + 2H2O


at 55 vol.-% CH

4


range of


5 bar abs, 200 °C


0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100


N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40


stoich

iometric

CH 4 + 2O

2 -> CO2 +

2H2O

stoich

iometric CH4 + 1.5O2 ->

CO + 2H2O


at 55 vol.-% CH

4


range of


5 bar abs, 25 °C


1 bar abs, 25 °C 5 bar abs, 25 °C

5 bar abs, 200 °C


0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


Pressure-time traces of Propene/O2 at 5 bar, 25 °C (1)

171 171.5 172 172.5 173 173.5 1740

100

200

300

Time [ms]0 100 200 300

0

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP08A;Propene=3, O2=97 Vol.%; 5bar abs; 25C.DAT

Propene = 3 vol.-%O2 = 97 vol.-%, 5 bar abs, 25 °C

0 20 40 600

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP142A-4%.DAT

26 26.5 27 27.5 28 28.5 290

25

50

75

100

125

150

Time [ms]


0 500 1000 1500 2000 2500 30000

5

10

15

20

25

30

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP76-2.25%.DAT

Propene = 2.25 vol.-%O2 = 97.75 vol.-%, 5 bar abs, 25 °C

topcenterbottom


0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


topcenterbottom


14 14.5 15 15.5 16 16.5 170

50

100

150

200

250

Time [ms]0 5 10 15 20 25 30

0

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]



0 2.5 5 7.5 10 12.5 150

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]


6.5 7 7.5 8 8.5 9 9.50

100

200

300

400

Time [ms]

Propene = 6 vol.-%,O2 = 94 vol.-%, 5 bar abs, 25 °C

0 5 10 15 200

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


5 5.5 6 6.5 7 7.5 80

100

200

300

400

500

Time [ms]



0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


topcenterbottom


3 3.5 4 4.5 5 5.5 60

100

200

300

400

500

Time [ms]0 5 10 15 20

0

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]



0 5 10 15 200

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


1 1.5 2 2.5 3 3.5 40

100

200

300

400

Time [ms]


0 5 10 15 200

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

File:PROP130A-18.2%.DAT

0 0.5 1 1.5 2 2.5 30

100

200

300

400

500

Time [ms]

Propene = 18.18 vol.-%,O2 = 81.82 vol.-%, 5 bar abs, 25 °C


0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


topcenterbottom


0 5 10 150

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


0 0.5 1 1.5 2 2.5 30

50

100

150

200

Time [ms]


0 5 10 150

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: Prope132a.dat, 28 vol.-%


0 0.5 1 1.5 2 2.5 30

200

400

600

800

Time [ms]

0 5 10 15 200

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

2 2.5 3 3.5 4 4.5 50

200

400

600

800

Time [ms]

File:PROP137A-33%.DAT



0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


topcenterbottom


5 10 15 200

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

File:PROP10A;Propene=35.5, O2=64.5 Vol.%; 5bar abs; 25C.DAT

4 4.5 5 5.5 6 6.5 70

100

200

300

400

500

Time [ms]

Propene = 35.5 vol.-%O2 = 64.5 vol.-%, 5 bar abs, 25 °C

10 15 20 250

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


11 11.5 12 12.5 13 13.5 140

100

200

300

400

Time [ms]



15 20 25 30 350

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

17 17.5 18 18.5 19 19.5 200

100

200

300

400

500

Time [ms]

File: Prope11A;Propene=39, O2=61 vol.-%, 5 bar abs, 25C


0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


topcenterbottom


15 20 25 30 350

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


22 22.5 23 23.5 24 24.5 250

100

200

300

400

500

Time [ms]


20 25 30 35 400

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]



26 26.5 27 27.5 28 28.5 290

100

200

300

400

500

Time [ms]

30 35 40 45 500

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


34 34.5 35 35.5 36 36.5 370

100

200

300

400

500

Time [ms]



0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


top



55 60 65 70 750

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]


61 61.5 62 62.5 63 63.5 640

50

100

150

Time [ms]


Pressure-time traces of stoich. Propene/O2/N2 at 5 bar, 25 °C (1)

0 10 20 30 40 500

10

20

30

40

50

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP15A; Propen=5.5, O2=25, N2=69.5 Vol.%;5bar abs;25C.DAT

Propene = 5.5 vol.-%O2 = 24.75 vol.-%, N2= 69.755 bar abs, 25 °C

0 10 20 30 400

25

50

75

100

Time [ms]

Pres

sure

[bar

abs

]

File: PROP208A-27%O2(erster Test).DAT

18 18.5 19 19.5 20 20.5 210

50

100

150

200

Time [ms]

Propene = 6 vol.-%O2 = 27 vol.-%, N2 = 675 bar abs, 25 °C

(first test)

0 10 20 30 400

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP209A-27%O2(zweiter Test).DAT

Propene = 6 vol.-%O2 = 27 vol.-%, N2 = 675 bar abs, 25 °C

(second test)

20 20.5 21 21.5 22 22.5 230

25

50

75

100

Time [ms]

0 10 20 30 40 50 60Propene C3H6 [Vol.-

8

90

1000

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

randeflagrati 5 bar a

range of detonativ

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO +

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O

propene/air

topcenterbottom



0 5 10 15 200

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File:PROP16A;Propen=6.9, O2=31, N2=62.1 Vol.%;5bar abs;25C.DAT

Propene = 6.9 vol.-%O2 = 31 vol.-%, N2 = 62.15 bar abs, 25 °C

12 12.5 13 13.5 14 14.5 150

50

100

150

200

250

Time [ms]

0 5 10 15 200

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP207A-35%O2.DAT

7 7.5 8 8.5 9 9.5 100

50

100

150

200

Time [ms]

0 5 10 15 200

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP17A;Propen=7.8, O2=35, N2=57.2 Vol.%;5bar abs;25C.DAT

7 7.5 8 8.5 9 9.5 100

100

200

300

400

Time [ms]


(second test)


(first test)


0 10 20 30 40 50 60Propene C3H6 [Vol.-%

80

90

1000

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

rangedeflagrative 5 bar abs

range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O

propene/air-m

topcenterbottom



0 5 10 15 200

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP18A;Propen=8.9, O2=40, N2=51.1 Vol.%;5bar abs;25C.DAT


4.5 5 5.5 6 6.5 7 7.50

100

200

300

400

Time [ms]

1 1.5 2 2.5 3 3.5 40

50

100

150

200

250

300

Time [ms]0 5 10 15 20

0

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

File: PROP216A-60%O2.DAT


0 5 10 15 200

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

File:PROP130A-18.2%.DAT

0 0.5 1 1.5 2 2.5 30

100

200

300

400

500

Time [ms]

Propene = 18.18 vol.-%,O2 = 81.82 vol.-%, 5 bar abs, 25 °C

0 10 20 30 40 50 60Propene C3H6 [Vol.-%

80

90

1000

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]

rangedeflagrative 5 bar abs

range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O

propene/air-m

top

center

bottom


Different explosion regimes (deflagration, heat explosion, detonation) of Methane/O2/N2 in a 20 l sphere at 1 and 5 bar abs, 25 °C and 200 °C

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100


N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40


range of


1 bar abs, 25 °Csto

ichiom

etric CH 4

+ 2O2 -

> CO 2 + 2H

2O

stoich

iometric CH4 + 1.5O 2 -

> CO + 2H2O



at 55 vol.-% CH

4

mixture reacts sometimesdetonative and sometimesas heat explosion

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100


N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40


stoich

iometric

CH4 + 2O

2 -> CO2 +

2H2O

stoich

iometric CH4 + 1.5O2 -

> CO + 2H2O


at 55 vol.-% CH

4


range of


5 bar abs, 200 °C


0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

1000

10

20

60

70

90

100


N 2 [V

ol.-%

] O2 [Vol.-%

]


80

50

30

40


stoich

iometric

CH 4 + 2O

2 -> CO2 +

2H2O

stoich

iometric CH4 + 1.5O2 ->

CO + 2H2O


at 55 vol.-% CH

4


range of


5 bar abs, 25 °C


1 bar abs, 25 °C 5 bar abs, 25 °C

5 bar abs, 200 °C


Pressure-time traces of Methane/O2 at 5 bar, 25 °C (1)

Methane CH [Vol.-%]4

N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

Met

hane

= 7

vol

.-%,

O =

93

vol.-

%,

5 ba

r abs

, 25

°C2

0 100 200 300 400 500 600 7000

10

20

30

Time [ms]

Pre

ssur

e [b

ar a

bs]

0 5 10 15 20 25 300

10

20

30

40

50

60

Time [ms]

Pre

ssur

e [b

ar a

bs]

23 23.5 24 24.5 25 25.5 260

25

50

75

100

125

Time [ms]

Met

hane

= 1

0 v

ol.-%

,O

= 9

0 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

13 13.5 14 14.5 150

50

100

150

200

Time [ms]0 5 10 15 20

0

20

40

60

Time [ms]

Pres

sure

[bar

abs

]

Met

hane

= 1

2 v

ol.-%

,O

= 8

8 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

topcenterbottom



topcenterbottom


N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

8 8.5 9 9.5 10 10.5 110

100

200

300

400

500

Time [ms]0 5 10 15 20

0

20

40

60

Time [ms]

Pres

sure

[bar

abs

]

Met

hane

= 1

4 v

ol.-%

,O

= 8

6 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

Met

hane

= 1

5 v

ol.-%

,O

= 8

5 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

5 5.5 6 6.5 7 7.5 80

50

100

150

200

Time [ms]0 5 10 15 20

0

20

40

60

Time [ms]

Pre

ssur

e [b

ar a

bs]

6 6.5 7 7.5 8 8.5 90

200

400

600

800

Time [ms]0 5 10 15 20

0

10

20

30

40

50

60

70

Time [ms]

Pres

sure

[bar

abs

]

2nd

test

:M

etha

ne =

15

vol

.-%,

O =

85

vol.-

%,

5 ba

r abs

, 25

°C2



topcenterbottom


N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

3 3.5 4 4.5 5 5.5 60

50

100

150

200

250

Time [ms]0 2.5 5 7.5 10

0

10

20

30

40

50

60

70

Time [ms]

Pres

sure

[bar

abs

]

Met

hane

= 1

7.5

vol

.-%,

O =

82.

5 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

3 3.5 4 4.5 5 5.5 60

100

200

300

400

500

Time [ms]0 2.5 5 7.5 10

0

10

20

30

40

50

60

70

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 2

0 v

ol.-%

,O

= 8

0 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

3 3.5 4 4.5 5 5.5 60

100

200

300

400

500

Time [ms]0 2.5 5 7.5 10

0

25

50

75

100

125

Time [ms]

Pres

sure

[bar

abs

]

2nd

test

:M

etha

ne =

20

vol

.-%,

O =

80

vol.-

%,

5 ba

r abs

, 25

°C2



topcenterbottom


N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

0 2.5 5 7.5 100

25

50

75

100

125

Time [ms]

Pre

ssur

e [b

ar a

bs]

1 1.5 2 2.5 3 3.5 40

100

200

300

400

Time [ms]

Met

hane

= 2

5 v

ol.-%

,O

= 7

5 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

0 2.5 5 7.5 100

25

50

75

100

125

Time [ms]

Pre

ssur

e [b

ar a

bs]

1 1.5 2 2.5 3 3.5 40

50

100

150

200

250

300

Time [ms]

2nd

test

:M

etha

ne =

25

vol

.-%,

O =

75

vol.-

%,

5 ba

r abs

, 25

°C2

0 2.5 5 7.5 100

25

50

75

100

125

Time [ms]

Pre

ssur

e [b

ar a

bs]

1 1.5 2 2.5 3 3.5 40

200

400

600

800

Time [ms]

3rd

test

:M

etha

ne =

25

vol

.-%,

O =

75

vol.-

%,

5 ba

r abs

, 25

°C2



topcenterbottom


N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

0 2.5 5 7.5 100

25

50

75

100

125

Time [ms]

Pres

sure

[bar

abs

]

0 0.5 1 1.5 2 2.5 30

50

100

150

200

250

300

Time [ms]

Methane = 35 vol.-%,O = 65 vol.-%, 5 bar abs, 25 °C

2

0 2.5 5 7.5 100

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

2 2.5 3 3.5 4 4.5 50

100

200

300

400

500

Time [ms]

Met

hane

= 4

0 v

ol.-%

,O

= 6

0 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

3 3.5 4 4.5 5 5.5 60

100200300400500600700800900

Time [ms]0 2.5 5 7.5 10

0

25

50

75

100

125

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 4

5 v

ol.-%

,O

= 5

5 vo

l.-%

, 5

bar a

bs, 2

5 °C

2



topbottom


N

[Vol

.-%]

2

O [Vol.-%

]

2 yellow range:possibly heat explosion

stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

5 10 15 20 250

25

50

75

100

125

150

Time [ms]

Pres

sure

[bar

abs

]

14 14.5 15 15.5 16 16.5 170

100

200

300

400

500

Time [ms]

Met

hane

= 5

0 vo

l.-%

,O

= 5

0 vo

l.-%

, 5

bar a

bs, 2

5 °C

2

0 25 50 75 100 125 1500

20

40

60

80

Time [ms]

Pres

sure

[bar

abs

]

Met

hane

= 5

5 vo

l.-%

,O

= 4

5 vo

l.-%

, 5

bar a

bs, 2

5 °C

2


Pressure-time traces of stoich. Methane/O2/N2 at 5 bar, 25 °C (1)

top

bottom


N

[Vol

.-%]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

0 100 200 300 4000

10

20

30

40

Time [ms]

Pres

sure

[bar

abs

]

Met

hane

= 1

0 v

ol.-%

,O

= 2

0 vo

l.-%

, N

= 7

0 vo

l.-%

,5

bar a

bs, 2

5 °C

2 2

0 5 10 15 20 25 300

20

40

60

80

Time [ms]

Pres

sure

[bar

abs

]

16 16.5 17 17.5 18 18.5 190

20

40

60

80

Time [ms]

Met

hane

= 1

5 v

ol.-%

,O

= 3

0 vo

l.-%

, N

= 5

5 vo

l.-%

,5

bar a

bs, 2

5 °C

2 2



topbottom

Methane CH [Vol.-%]4N

[V

ol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

0 5 10 15 200

20

40

60

Time [ms]

Pre

ssur

e [b

ar a

bs]

4 4.5 5 5.5 6 6.5 70

20

40

60

Time [ms]

0 5 10 15 200

50

100

150

Time [ms]

Pre

ssur

e [b

ar a

bs]

3 3.5 4 4.5 5 5.5 60

50

100

150

Time [ms]

Met

hane

= 2

0 v

ol.-%

,O

= 4

0 vo

l.-%

, N

= 4

0 vo

l.-%

,5

bar a

bs, 2

5 °C

2 2

Met

hane

= 2

5 v

ol.-%

,O

= 5

0 vo

l.-%

, N

= 2

5 vo

l.-%

,5

bar a

bs, 2

5 °C

2 2




N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

Met

hane

= 1

0 v

ol.-%

,O

= 9

0 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

0 10 20 30 400

5

10

15

20

25

30

Time [ms]

Pre

ssur

e [b

ar a

bs]

12 12.5 13 13.5 14 14.5 150

10

20

30

40

Time [ms]0 5 10 15 20

0

10

20

30

40

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 1

2.5

vol.-

%,

O =

87.

5 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

8 8.5 9 9.5 10 10.5 110

10

20

30

40

Time [ms]0 5 10 15 20

0

10

20

30

40

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 1

4 vo

l.-%

,O

= 8

6 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

topcenterbottom




N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

topcenterbottom

6 6.5 7 7.5 8 8.5 90

100

200

300

400

Time [ms]0 2.5 5 7.5 10

0

10

20

30

40

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 1

5 vo

l.-%

,O

= 8

5 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

4 4.5 5 5.5 6 6.5 70

100

200

300

400

Time [ms]0 2.5 5 7.5 10

0

10

20

30

40

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 1

7.5

vol.-

%,

O =

82.

5 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

0 2.5 5 7.5 100

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

3 3.5 4 4.5 5 5.5 60

100

200

300

400

Time [ms]

Met

hane

= 2

0 vo

l.-%

,O

= 8

0 vo

l.-%

,,5

bar a

bs, 2

00 °

C2




N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

top

centerbottom

0 2.5 5 7.5 100

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

2 2.5 3 3.5 4 4.5 50

100

200

300

400

Time [ms]

Met

hane

= 2

5 vo

l.-%

,O

= 7

5 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

Met

hane

= 4

0 v

ol.-%

,O

= 6

0 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

0 2.5 5 7.5 100

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

2 2.5 3 3.5 4 4.5 50

100

200

300

400

500

Time [ms]

4 4.5 5 5.5 6 6.5 70

100

200

300

400

500

Time [ms]0 2.5 5 7.5 10

0

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 4

5 v

ol.-%

,O

= 5

5 vo

l.-%

,,5

bar a

bs, 2

00 °

C2




N

[Vol

.-%]

2

O [Vol.-%

]

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

top

centerbottom

0 5 10 15 200

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

10 10.5 11 11.5 12 12.5 130

50

100

150

200

250

Time [ms]

0 100 200 300 4000

10

20

30

40

50

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 5

0 v

ol.-%

,O

= 5

0 vo

l.-%

,,5

bar a

bs, 2

00 °

C2

Methane = 55 vol.-%,O = 45 vol.-%,,5 bar abs, 200 °C

2

0 200 400 600 8000

10

20

30

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 6

2 vo

l.-%

,O

= 3

8 vo

l.-%

,,5

bar a

bs, 2

00 °

C2



0 5 10 15 20 25 300

10

20

30

40

Time [ms]

Pre

ssur

e [b

ar a

bs]

Met

hane

= 1

5 v

ol.-%

,O

= 3

0 vo

l.-%

,,N

= 5

5 vo

l.-%

, 5

bar a

bs, 2

00 °

C

2 2

0 2.5 5 7.5 10 12.5 150

10

20

30

40

50

Time [ms]

Pre

ssur

e [b

ar a

bs]

6 6.5 7 7.5 8 8.5 90

10

20

30

40

50

Time [ms]

Met

hane

= 2

0 v

ol.-%

,O

= 4

0 vo

l.-%

,,N

= 4

0 vo

l.-%

, 5

bar a

bs, 2

00 °

C

2 2

0 2.5 5 7.5 10 12.5 150

10

20

30

40

50

Time [ms]

Pre

ssur

e [b

ar a

bs]

6 6.5 7 7.5 8 8.5 90

10

20

30

40

50

Time [ms]

2nd

test

:M

etha

ne =

20

vol

.-%,

O =

40

vol.-

%,,

N =

40

vol.-

%,

5 ba

r abs

, 200

°C

2 2 Methane CH [Vol.-%]4

N

[Vol

.-%]

2

O [

2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

topcenterbottom



0 2.5 5 7.5 100

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

3 3.5 4 4.5 5 5.5 60

25

50

75

100

Time [ms]

0 2.5 5 7.5 100

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

1 1.5 2 2.5 3 3.5 40

25

50

75

100

Time [ms]

Met

hane

= 2

5 v

ol.-%

,O

= 5

0 vo

l.-%

,,N

= 2

5 vo

l.-%

, 5

bar a

bs, 2

00 °

C

2 2

Met

hane

= 3

0 v

ol.-%

,O

= 6

0 vo

l.-%

,,N

= 1

0 vo

l.-%

, 5

bar a

bs, 2

00 °

C

2 2

0 2.5 5 7.5 10 12.5 150

25

50

75

100

Time [ms]

Pre

ssur

e [b

ar a

bs]

7.5 8 8.5 9 9.5 10 10.50

25

50

75

100

Time [ms]

Note:This is not on the stoichiometric line!!Methane = 15 vol.-%,O = 55 vol.-%,,N = 30 vol.-%, 5 bar abs, 200 °C

2

2


N

[Vol

.-%]

2

O2


stoich

iometric C

H+ 2O

-> CO

+ 2H O

4

2

2

2

top

centerbottom


Summary of the differences in the pressure time diagrams betweenexplosions in vessels that were triggered by a thermal ignition andended up as deflagration, “heat explosion” or detonation

course of explosion deflagration heat explosion detonation

presence of pressure pulse

no yes yes

width of pressure pulse at half height [µs]

(not applicable)

100 - 200 < 50

height of pressure pulse divided by pressure in mixture just before its occurrence

(not applicable)

typically 4 to 7 (equals deflagration pressure ratio of the

precompressed unreacted mixture)

typically 15 to 50 (due to too small

sampling rate the true maximum was

presumably mostly missed)

precompression ratio at the moment when pressure pulse occurs

(not applicable)

5 – 10 (largest value equals

pex/pinitial of the corresponding gas

mixture)

1 – 20 (largest value equals

pex/pinitial of the corresponding gas

mixture) "oscillations" in reaction gases after occurrence of pressure pulse

no oscillations anyway

no oscillations massive oscillations (due to shock front bouncing backwards and for-wards in reaction

gases) acoustic sound heard outside the vessel

nothing “click” prolonged whistle


Heat explosion – tentative explanation of the course of events

024

1086

12

radial position r/R0 0 1

hot reaction gases

flam

e fro

ntpr

ecom

pres

sed

unre

acte

d m

ixtu

re

pres

sure

/pin

itial

Before heat explosion:Reaction rate sufficiently slow to allow for pressure equilibrium over entire sphere

Pressure as function of radial position in 20 l sphere (pinitial = 1 bar abs) justbefore heat explosion occurs in theprecompressed, unreacted mixture(R0 = 17 cm)

After heat explosion:reaction gases flow to the central part of the sphere and pressure equilibrium is attained

At heat explosion:Immediate temperature rise and hence also pressure rise in the shell so far unreacted, but heated by adiabatic compression. The induction time must be of the order of 0.1 ms or even less, otherwise the flame front of the initial deflagration would have run through the thin shell of unreacted mixture before the heat explosion could develop.


Temperatures obtainable by adiabatic compression

( )γ

γ 1−

⎟⎠⎞

⎜⎝⎛⋅=

initialfinal

initialfinal pp

TT

pfinal/pinitial Tfinal [°C] resulting for different values of γ in case that Tinitial = 35 °C = 308 K

Tfinal [°C] resulting for differrent values of γ in case that Tinitial = 200 °C = 473 K

γ = 1,4 γ = 1,3 γ = 1,2 γ = 1,1 γ = 1,4 γ = 1,3 γ = 1,2 γ = 1,11,5 72,8 65,2 56,5 46,6 258,1 246,4 233,1 217,82 102,5 88,4 72,7 55,0 303,6 282,0 257,9 230,83 148,6 123,9 96,9 67,3 374,4 336,5 295,0 249,74 184,7 151,1 115,1 76,4 429,9 378,3 322,9 263,55 214,8 173,5 129,8 83,5 476,1 412,7 345,5 274,56 240,9 192,7 142,2 89,5 516,2 442,2 364,6 283,77 264,0 209,6 153,0 94,6 551,7 468,1 381,2 291,58 284,9 224,7 162,6 99,1 583,8 491,3 395,9 298,49 304,0 238,4 171,2 103,1 613,1 512,4 409,2 304,610 321,7 251,0 179,1 106,7 640,2 531,7 421,3 310,112 353,5 273,5 193,0 113,1 689,1 566,3 442,7 319,914 381,7 293,3 205,2 118,5 732,4 596,7 461,3 328,216 407,1 311,0 215,9 123,3 771,5 623,9 477,8 335,618 430,4 327,1 225,6 127,6 807,2 648,6 492,7 342,120 451,9 341,9 234,4 131,4 840,2 671,3 506,3 348,1

Formula for temperature increase due to adiabatic compression:

Temperatures may well lie above the ignition temperatures themixtures presumably have in the precompressed state!


Autoignition temperatures of Propene/O2/N2Propene [Vol.-%]

O2 [Vol.-%]

N2 [Vol.-%]

Autoignition Temperature (AIT) [°C]

AIT [°C] at Pinitial = 5 bar abs for Propene/O2 mixtures 4.46 95.54 0 280 7 93 0 270 10 90 0 270 20 80 0 260 30 70 0 260 40 60 0 250 50 50 0 250 60 40 0 250 AIT [°C] at Pinitial = 5 bar abs for stoichiometric (with respect to CO2 and H2O-formation) Propene/O2 mixtures, i.e. Propene:O2 = 1 : 4.5 4.46 20.07 75.47 280 7 31.5 61.5 270 10 45 45.0 270 AIT [°C] at Pinitial = 1 bar abs for stoichiometric (with respect to CO2 and H2O-formation) Propene/O2 mixtures, i.e. Propene:O2 = 1 : 4.5 4.46 20.07 75.47 485 (CHEMSAFE, DIN-method in open Erlenmeyer

flask) 7.0 31.5 61.5 410 10.0 45.0 45.0 310 15.5 70.0 14.5 290

0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

0

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O



0

1

2

3

4

5

700 800 900 1000 1100 1200

Temperature, K

Indu

ctio

n tim

e, m

s

C3H6-O2-N2=20-40-40

C3H6-O2-N2=5-95-0

0 10 20 30 40 50 60 70 80 90 100Propene C3H6 [Vol.-%]

10

20

30

40

50

60

70

80

90

100

O2 [Vol.-%

]

0

10

20

30

40

50

60

70

80

90

100

N 2 [V

ol.-%

]


range of detonative

explosion

stoich

iometric C3H6 +

1.5 O2 -> 3 CO + 3 H2

stoich

iometr

ic C 3H

6 + 3

O 2 -> 3

CO +

3 H2O

stoich

iometr

ic C 3H

6 + 4.

5 O2 -

> 3 C

O 2 + 3

H 2O


Induction times of two mixture compositions lying in the yellow range of the explosion diagram at 5 bar abs

Propene= 5 vol.-%, O2 = 95 Vol.-%

Propene= 20 vol.-%,O2 = 40 vol.-%,N2 = 40 vol.-%

Calculation by A.A. Konnov, Department of Mechanical EngineeringVrije Universiteit Brussel (VUB),based on the rate coefficients for all elementary reactions


Is “heat explosion” a realistic assumption for what happens in yellow range of the explosion triangle ?

- temperatures achieved by adiabatic compression lie well abovethe autoignition temperature, i. e. heat explosion is possible in principle

- but: induction times calculated on the basis of the rate coefficientsof the elementary reactions are still far too long(The induction time would have to be of the order of 0.1 ms or even less, otherwise the flame front of the initial deflagration would have run already through the thin shell of unreacted mixture before the heat explosion can develop).

- including the influence of thermal radiation from the cental part of the spheredoes not give a substancial reduction in induction times either (calculation of Hans Pasman)

⇒ Not really clear what happens in theyellow range of the explosion triangle


Summary on explosion regimes of combustible/air/O2 mixturesignited with a thermal ignition source in vessel-like geometry

There are three explosion regimes: deflagration, „heat explosion“, detonation

The „heat explosion“ regime becomes much smaller with increasing initialpressure

Mixtures of type combustible/air seem to remain deflagrative even at elevatedpressures and temperatures. However, the data collected so far do not allow to exclude that the detonativeregime will expand down to the air line when going to extremely high initialpressures and large vessel volumes.

What really happens in the „heat explosion“ regime is not yet really understood,maybe the pressure time curves are just due to failed DDT‘s

The detonative range in the 20 l sphere is discernibly smaller than thepotentially detonative range



Introduction







Schematic pressure-time trace of a detonative pressure pulse

Pinitial

deflagration pressure ratioof gas mixture

von Neumann spike, about twice as high as PCJ

PCJ , about twice the deflagration pressure ratio of the gas mixture

width < 1 µs => much less than cycle time of anyeigenfrequency of the containment

=> not „noticed“ by the containment and notregistered by the fastest available pressure sensors

Pre

ssur

e/P

initi

al

5

10

15

20

25

30

35

45

40

50

0time

unburned gas mixturehot reaction products flamefront coupledwith shockfront, v >> vsoundl

pressure sensor, flushwith inner surface of wall

Leading edge of detonation peakhas almost infinite slope (rise time < 1µs)

width of „Taylor expansion fan“: ca. 20 µs – 50 µs in laboratoryscale containments, longer in structures of larger dimensions(less than one quarter of the time interval over which the peak has already propagated)


Pressure-time diagrams recorded during a detonation in a long pipe at different locations (1/2)

Example: Propane/O2, stoichiometric, Pinitial = 6 bar abs, Tinitial = 20 °C, pipe 25x2, L = 5 m, side-on pressure

location of ignition

P1 P2 P3 P4 1025 mm 1970 mm

2915 mm 3855 mm

5000 mm

pipe: 25 x 2

v = Δs/Δt= 0.945m/0.375ms = 2519 m/s

Pdet ≅ 35*Pinitial

(same value at all sensors)


Pressure-time diagrams recorded during a detonation in a long pipe at different locations (2/2)Experiment:Ethylene/air stoichiometric,14 bar abs, 20 °C, side-on pressure, pipe: φi = 44.3 mm, φo = 48.3 mm, L = 8 m, turbulence enhancer in front of ignitionsource to reduce run-up distance

P3 P2 P1

2 m 1.5 m 0.5 m location of ignition

22 23 24 25 260

50

100

150

200

250

300

Time [ms]

Pres

sure

[bar

abs

]

22 23 24 25 260

100

200

300

Time [ms]Pr

essu

re [b

ar a

bs]

22 23 24 25 260

100

200

300

400

500

Time [ms]

Pres

sure

[bar

abs

]

P2

P1

P3

Δt = 1.033 ms

Δs = 1.5 m

vdet=Δs/Δt=1936 m/s

vdet=Δs/Δt=1883 m/s

Δs = 2 m

Δt = 0.796 ms


Qualitative consideration: differences between the pressures produced in a long pipe by a deflagration and by a detonation (2/2)

Detonative Explosion (predetonation stage necglected)

unburnt gas mixturehot reaction products flamefront coupledwith shockfront, v >> vsoundl

Pex

/Pin

itial

25

151050

20P = 9.5*Pinitial

P = Pinitial

extension:in space ca. 10 – 20 cmIn time ca. 20 – 50 µs

Location of ignition

distance from left pipe end

Pdet = 2*9.5*Pinitial

Example: Propane/air, stoichiometric, Tinitial = 20 °C, explosion pressure ratio: 9.5 (simplification: no heat loss to wall)

P is different at different locations in the pipe:- behind shockfront: P = 9.5*Pinitial (9.5 is explosion pressure ratio of mixture)- at shockfront: P = 2*9.5*Pinitial (i.e. about twice as high as behind shockfront)- in front of shockfront: P = Pinitial

(reason: reaction gases would like to expand into region ahead of shockfront, but speed of sound in hot reaction gases only about 1000 m/s whereas shockfront propagates with about 1700 m/s)


Detonation pressures Pdet in long pipes (L >> Lpredet, no precompression)

detonationfront

pressure sensor,flush with inner surface of wall

Stable Detonation, side-on pressure (i. e. in plane perpendicular to shockfront)

Stable Detonation, reflected pressure (i. e. in plane parallel to shockfront, e. g. blind flange)

detonationfront

pressure sensor,flush with inner surface of flangel

2 ≤ Freflec ≤ 2.5

PCJ is the so-calledChapman-Jouguet-pressure ratioof the explosive gas mixture

Pdet = Pinitial * PCJ

Pdet = Pinitial * PCJ * Freflec

Important:The pipe directly ahead of the blind flangeexperiences the reflected pressure as well. Thelength of this section corresponds to the axial extension of the taylor expansion fan. (In lab-scale equipment of up to 5 m length a section of about 3 pipe diameters from the blind flange back into the pipe is affected, in longerpipes this section increases).


Detonation pressures Pdet in long pipes (L >> Lpredet, no precompression)

Reflected pressure, if DDT occurs directly in front of blind flange (a very rare case!)

2 ≤ Freflec ≤ 2.5

Side-on pressure at location where Deflagration-to-Detonation transition (DDT) occurs

flame front of initialdeflagration has accelerated

to a very high speed

first occurrence of ignitionby adiabatic compressionin precompressed mixture; generation of shock front coupled with flame front, propagating leftwards

location ofignition

Pdet = Pinitial * PCJ * FDDT * Freflec

1.5 ≤ FDDT ≤ 2Pdet = Pinitial * PCJ * FDDT


to a very high speed first occurrence of ignitionby adiabatic compressionin precompressed mixture;generation of shock front coupled with flame front, propagating leftwards

1.5 ≤ FDDT ≤ 2

(continued)

Important:The pipe directly ahead of the blind flangeexperiences the reflected pressure as well. Thelength of this section corresponds to the axial extension of the taylor expansion fan. (In lab-scale equipment of up to 5 m length a section of about 3 pipe diameters from the blind flange back into the pipe is affected, in longerpipes this section increases).


Chapman-Jouguet pressure ratios PCJ calculated by STANJAN

Solid lines:Calculated Chapman-Jouguetpressure ratios for pinitial = 5 bar abs(by Prof. M. Braithwaite withsoftware package STANJAN)

0

10

20

30

40

0 2 4 6 8 10 12 14 16 18 20Propene conc. in stoich. Propene/O2/N2-mixture [vol.-%]

pcj/p

initi

al

(Cha

pman

-Jou

guet

pre

ssur

e di

vide

d by

pin

itial)

0

5

10

15

20

pex/

p ini

tial (

defla

grat

ion

pres

sure

ra

tio)

calculated Pcj/Pinitial at 5 bar abs, 25°Cmeasured defl. pr.-ratios Pex/Pinitial at 5 bar abs, 25 °C

0

10

20

30

40

50

0 10 20 30 40 50 60 70 80Propene concentration in Propene/O2-mixture [vol.-%]

p cj/p

initi

al

(Cha

pman

-Jou

guet

pre

ssur

e di

vide

d by

pin

itial

)

0

5

10

15

20

25

p ex/p

initi

al (d

efla

grat

ion

pres

sure

ra

tio)

Pcj/Pinitial at 5 bar abs, 25 °CPcj/Pinitial at 5 bar abs, 200°Cmeasured defl. pr.-ratios Pex/Pinitial at 5 bar abs, 25°Cmeasured defl. pr.-ratios Pex/Pinitial at 5 bar abs, 200°C

Symbols: Measured deflagration pressureratios (scale on right side of plots)

The values are just about half of theChapman-Jouguet pressure ratios!!

PC

J(C

hapm

an-J

ougu

etpr

essu

rera

tio)

PC

J(C

hapm

an-J

ougu

etpr

essu

rera

tio)

Example: Propene/O2/N2


0

5

10

15

20

0 5 10 15 20Methane concentration in Methane/air-mixture [vol.-%]

PCJ

Cha

pman

-Jou

guet

det

onat

ion

pres

sure

rat

io

5 bar abs, 25 °C5 bar abs, 200 °C


0

5

10

15

20

25

30

35

0 10 20 30 40 50 60 70 80Methane concentration in Methane/O2-mixture [vol.-%]

pcj/p

initi

al

(Cha

pman

-Jou

guet

pre

ssur

e di

vide

d by

Pin

itial

)

0

2,5

5

7,5

10

12,5

15

17,5

p ex/p

initi

al (d

efla

grat

ion

pres

sure

ra

tio)

calculated Pcj/Pinitial at 5 bar abs, 25 °Ccalculated Pcj/Pinitial at 5 bar abs, 200 °Cmeasured defl. Pr.-ratios Pex/Pinitial at 5 bar abs, 25°Cmeasured defl. Pr.-ratios Pex/Pinitial at 5 bar abs, 200°C

PC

J(C

hapm

an-J

ougu

etpr

essu

rera

tio)

PC

J(C

hapm

an-J

ougu

etpr

essu

rera

tio)

Example: Methane/O2/N2



0

5

10

15

20

0 10 20 30 40 50 60 70 80 90 100H2 concentration in H2/O2-mixture [vol.-%]

p cj/p

initi

al

(Cha

pman

-Jou

guet

pre

ssur

e di

vide

d by

pin

itial

)

0

2,5

5

7,5

10

p ex/p

initi

al d

efla

grat

ion

pres

sure

ra

tio)

calculated detonation pr.-ratios PCJ/P initial at 1 bar abs, 20°C

calculated detonation pr.-ratios PCJ/P initial at 5 bar abs, 20°C

calculated detonation pr.-ratios PCJ/P initial at 5 bar abs, 200°Cmeasured pex/pinitial at 1 bara bs, 20 °C

0

5

10

15

20

0 10 20 30 40 50 60 70 80H2 concentration in H2/Air-mixture [vol.-%]

pcj/p

initi

al

(Cha

pman

-Jou

guet

pre

ssur

e di

vide

d by

pin

itial

)

0

2,5

5

7,5

10

p ex/p

initi

al d

efla

grat

ion

pres

sure

ra

tio)

calculated detonation pr.-ratios PCJ/Pinitial at 1 bar abs, 20°Ccalculated detonation pr.-ratios PCJ/Pinitial at 5 bar abs, 20°Ccalculated detonation pr.-ratios PCJ/Pinitial at 5 bar abs, 200°Cmeasured pex/pinitial at 1 bar abs, 20 °Cmeasured pex/pinitial at 5 bar abs, 20 °Cmeasured pex/pinitial at 5 bar abs, 200°C

Example: H2/O2/N2


Chapman-Jouguet pressure ratios PCJ calculated on basis of detonation velocity

Remarks:For using STANJAN various thermodynamic parameters of the reaction componentsmust be known. If these are not available, the detonation velocity is experimentallyeasily aminable with high precision by recording the side-on pressure of thepropagating detonation at different axial locations in the pipe with piezoelectricpressure sensors. Since the absolute signal value, which is actually the quantity oneis looking for, is often prone to errors, one has to use the „bypass“ over the speed.

PCJ = pdet /pinitial = (γ *M2+1)/(γ+1)

≈ (γ * M2)/(γ+1)

= (D2 * MW)/(R*Tinitial*(γ+1))

= ρ/pinitial * D2/(γ+1)

M = D/c Mach numberD propagation speed of detonation [m/s]c = (γ * pinitial /ρ)0.5 speed of sound in the unreacted gas mixture [m/s]ρ density of unreacted gas mixture [kg/m3]MW mean molar mass of unreacted gas mixture [kg/mol]R=8.314 universal gas constant [J/(mol*K)]γ cp/cv, for diatomic gases γ = 1.4 Tinitial , pinitial initial temperature [K], initial pressure [Pa] of gas mixturepdet side on pressure of stable detonation

meaning of symbols:


General remarks on Chapman-Jouguet pressure ratios PCJ

Chapman-Jouguet pressure ratios can be calculated by e.g. STANJAN (freeware, STANJAN Chemical Equilibrium Solver v4.01, Stanford University 2003)

Chapman-Jouguet pressure ratios are with good precision twice as high as the explosion pressure ratio found for deflagrative explosion:

Chapman-Jouguet pressure ratio is inversely proportional to the absolute initialtemperature. (Propagation speed of detonation is almost independent of Tinitial !)

If thermodynamic quantities required by STANJAN are not available for all components of the considered explosive gas mixture, PCJ can be calculated on the basis of the experimentally determined detonation speed.

- stoichiometric combustible/air- mixtures at 20°C: 16 ≤ PCJ ≤ 20 - stoichiometric combustible/O2-mixtures at 20 °C: 30 ≤ PCJ ≤ 50


Example: bulging out of a pipe end due to reflected pressure

Experiment:Acetylene, 8 bar abs, 20 °C, pipe220.9 x 8.2, i.e. φi = 204.5 mm, material: St35.8, Rp0.2 = 230 N/mm2, PRp0.2=184 bar, L = 8 m, detonativeignition source to reduce run-up distance;side-on pressure ca. 400 bar,reflected pressure ca. 800 bar

Increase of tube diameter directly in front of blind flange to 117 % of original value

no increase in diameter in the section that has only been exposed to the side-on pressure


Example: Rupture of pipe end due to reflected pressure

Experiment:Ethylene/air stoichiometric, 17 bar abs, 20 °C, pipe 76.1 x 2.6, i.e. φi = 70.9, material: 1.4541, Rp0.2 = 210 N/mm2, PRp0.2=154 bar, L = 8 m;side-on pressure ca. 340 bar,reflected pressure ca. 765 bar

increase in diameter to 105 % of original value in the section that has only been exposed to the side-on pressure

end of tube, which was exposed to the reflected pressure, is fragmented


Example: bulging out of a pipe wall due to theextra pressure at the point where the DDT occurs

Localized bulging of tube is attributed to the location of the deflagration to detonation transition

Experiment:Acetylene, 24 bar abs, 20 °C, pipe 3.17 x 0.5, φi = 2.17 mm, material: 1.4541, Rp0.2 ≥ 250 N/mm2, PRp0.2 ≥ 1152 bar, kaltgezogen, L = 10 m



Introduction






How does precompression („pressure piling“) come into existence?

During the initial deflagrative stage of the explosion each volume element thatreacts through expands by a factor equal to the explosion pressure ratio at theexpense of the volume available for the yet unreacted mixture.

If this volume is large compared to the volume occupied by the reaction gasesformed during initial deflagrative stage, the pressure in the yet unreactedmixture will almost stay the same as at the moment of ignition (P = Pinitial).

However, if this volume is small, the yet unreacted mixture will beprecompressed. When the deflagration to detonation transition then occurs, thedetonation will not propagate in a mixture at pressure P = Pinitial, but at P = Fprecomp * Pinitial

Fprecomp may attain any value between 1 and the explosion pressure ratio of thegas mixture (up to 10 for combustible/air-mixtures, up to 24 for combustible/O2-mixtures).

The temperature rise that comes along with the fast and hence adiabaticcompression will slightly alleviate the detonative pressure Pdet. This isaccounted for by the Factor Ftemp (details see next slide)

In the formulae given beforehand for Pdet, Fprecomp and Ftemp will appear as additional factors


Temperature factor Ftemp

The temperature factor Ftemp accounts for the reduction of the Chapman-Jouguetpressure ratio due to the rise in temperature of the unburned mixture broughtabout by the precompression during the initial deflagrative stage of the explosion.

I: Temperature Tfinal of unburned mixture attained by adiabatic compression:

( )

γγγ

γ)1(

1−

−

⋅=⎟⎠⎞

⎜⎝⎛⋅= precompinitial

initial

finalinitialfinal FTp

pTT

II: Chapman-Jouguet pressure ratio is inversely proportional to the temperature thegas mixture exhibits at the moment of detonation (here denoted by Tfinal).

with: γ = cp/cv (γ = 1.4 for ideal gases)

Ftemp results from the combined effect of I: and II:

γγ )1(

1−

⎟⎟⎠

⎞⎜⎜⎝

⎛==

precompfinal

initialtemp FT

TF

Tinitial = temperature at moment of ignition



152,3299,0462,0638,250

148,2289,0444,3611,245

143,7278,1425,1582,040

138,7266,0403,9550,035

133,0252,3380,3514,530

126,3236,6353,4474,525

118,3218,0321,9428,420

114,6209,4307,6407,618

110,4200,0292,1385,016

105,8189,6274,9360,414

100,5177,9255,8333,112

94,4164,4234,0302,310

87,0148,4208,5266,88

77,7128,7177,6224,26

65,0102,5137,3169,84

44,461,576,790,32

36,245,854,261,61,5

30,034,237,840,91,2

γ = 1,1γ = 1,2γ = 1,3γ = 1,4

Tfinal [°C] for different values of γ = cp/cvPfinal/Pinitial

Tinitial = 25 °C = 298 K

( )γ

γ 1−

⎟⎠⎞

⎜⎝⎛⋅=

initialfinal

initialfinal pp

TTFormula for temperature increase due to adiabatic compression:

402,0634,9893,61173,450

395,6619,1865,61130,545

388,5601,7835,11084,040

380,5582,5801,41033,235

371,4560,8763,9977,030

360,8535,8721,2913,525

348,1506,3671,3840,220

342,1492,7648,6807,218

335,6477,8623,9771,516

328,2461,3596,7732,414

319,9442,7566,3689,112

310,1421,3531,7640,210

298,4395,9491,3583,88

283,7364,6442,2516,26

263,5322,9378,3429,94

230,8257,9282,0303,62

217,8233,1246,4258,11,5

207,9214,6220,3225,31,2

γ = 1,1γ = 1,2γ = 1,3γ = 1,4




Example 1: precompression in a pipe

P3 P1

P2

first occurrencedetonation front

flame front of initialdeflagration

hot reaction products

precompressedunburned gas mixture

If the pipe is only slightly longer than the predetonation distance, the unburnedgas which is remaining at the moment when the DDT occurs may have beenprecompressed by a factor Fprecomp by the initial deflagrative stage of thecombustion.

Fprecomp may attain any value between 1 and the explosion pressure ratio of thegas mixture (up to 10 for combustible/air-mixtures, up to 24 for combustible/O2-mixtures).

The temperature rise that comes along with the fast and hence adiabaticcompression will slightly alleviate the detonative pressure Pdet. This isaccounted for by the Factor Ftemp


hot, gaseousreaction products

deflagrativeflamefront


pipe, slightly longer than Lpredet

vessel

Precompressed, unburned gas mixture

Example 2: precompression in the vessel-pipe configuration

If in the vessel the DDT does not happen because of the unfavourable L/D-ratioand if the volume of the pipe is small compared to the volume of the vessel, theprecompression factor may come close to the highest possible value, i. e. theexplosion pressure ratio.The highest possible value is usually not attained, because the available time istoo short to pressurize the pipe up to the same pressure as in the vessel.

This configuration occurs frequently in practical applications, because vesselsoften have nozzles onto which short pipe segments with a block valve arewelded.


Example 3: precompression in empty vessels(i.e. without packing inside)

hot reactionproducts

First occurrence of detonation front

Flamefront of initial deflagration

Precompressed, unburned mixture


vessel (here spherical, L/D = 1)

If there is a transition from deflagration to detonation in the vessel, precompression will almost always occur, because the diameter is usually notmuch larger than the predetonation distance. The precompression factormay attain the highest possible value, i. e. the explosion pressure ratio.

Reference: GCT report 105.0428.3N, 106.0104.3I


Detonation pressures Pdet in pipes with precompression (1/2)

detonationfront

pressure sensor,flush with inner surface of wall

Side-on pressure (i. e. in plane perpendicular to shockfront)

Reflected pressure (i. e. in plane parallel to shockfront, e. g. blind flange)

detonationfront

pressure sensor,flush with inner surface of flangel

Important:about 3 pipe diameters from the blind flangeback into the pipe this higher pressure also acts on the wall of the pipe!

Pdet = Pinitial * PCJ* Fprecomp * Ftemp

Pdet = Pinitial * PCJ * Freflec* Fprecomp * Ftemp


Detonation pressures Pdet in pipes with precompression (2/2)

Reflected pressure, if DDT occurs directly in front of blind flange (a very rare case!)

Side-on pressure at location where Deflagration-to-Detonation transition (DDT) occurs


to a very high speed

first occurrence of ignitionby adiabatic compressionin precompressed mixture; generation of shock front coupled with flame front, propagating leftwards

location ofignition

Pdet = Pinitial * PCJ * FDDT * Freflec * Fprecomp * Ftemp

Pdet = Pinitial * PCJ * FDDT * Fprecomp * Ftemp


to a very high speed first occurrence of ignitionby adiabatic compressionin precompressed mixture;generation of shock front coupled with flame front, propagating leftwards

Important:about 3 pipe diameters from the blind flangeback into the pipe this higher pressure also acts on the wall of the pipe!


Detonation pressure Pdet acting on the wall of a vessel (almostalways with precompression)

x Chapman-Jouguet pressure ratio of the mixture at the temperaturethe mixture exhibits at the moment of ignition (PCJ)

x Precompression factor (FPrecomp)

Initial pressure in vessel at moment of ignition (Pinitial)

x Temperature factor (FTemp)

x Factor accounting for reflection of stable detonation at wall (Freflec )

Pdet =

x Factor accounting for extra pressure if DDT happens directlybefore wall (FDDT), otherwise factor is 1

Pdet = Pinitial * PCJ * Fprecomp * Ftemp * Freflec * (FDDT or 1, depending on where DDT happened)


Example: Rupture of the wall of a pipe installed in thevessel-pipe configuration due to precompression

Pinitial = 25 bar abs,Tinitial = 250 °C

99.5 vol.-% N2O0.5 vol.-% Tetradecane

Ignition in center of sphere

20 l sphere

closed Valve(to vacuum pump)

10x2 pipe (1.4541)rupture pressure in hydraulic test: 3480 bar

rupture at locationof DDT in precompressedmixture

detonation in thissection,outer diameteris 102 % to 110 % of original value

only deflagrationin this section,outer diameteris not increased

Rest of the bendhas been burnedoff by outflowinghot reaction gases



Introduction






Precompression factors Fprecomp in the heat explosion and detonative range of explosion diagrams of Propene/O2/N2 at 5 bar abs, 25 °C and 200 °C

0

5

10

15

20

25

0 10 20 30 40 50

Propene concentration in Propene/O2-mixture [vol.-%]

phea

t_in

itial

/pin

itial

or p

det_

initi

al/p

initi

al 5 bar abs, 25 °C

5 bar abs, 200 °C

orange filled symbols: heat explosionblue and red symbols: detonation

0

5

10

15

0 5 10 15 20Propene conc. in (Propene:O2=1:4.5)/N2-mixture [vol.-%]

phea

t_in

itial

/pin

itial

or p

det_

initi

al/p

initi

al 5 bar abs, 25 °C

5 bar abs, 200 °C

Propene/O2-mixture stoichiometric Propene/O2/N2-mixture(Propene:O2=1:4.5)

Note: on stoichiometric line at 200 °C only deflagration for one test with 7.8 vol.-% Propene

F pre

com

p

F pre

com

p


Upper limit for precompression factors

The precompression factors attain at maximum the deflagration pressure ratio!

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90Propene concentration in Propene/O2-mixture [vol.-%]

p ex/p

initia

l

1 bar abs, 25 °C5 bar abs, 25 °C10 bar abs, 25 °C1 bar abs, 200 °C5 bar abs, 200 °C10 bar abs, 200 °C

18.1

8 vo

l.-%

: sto

ichi

omet

ric c

ompo

sitio

n fo

r C

3H6 +

4.5

O2 -

> 3

CO

2 + 3

H2O

25 v

ol.-%

: sto

ichi

omet

ric c

ompo

sitio

n fo

r C

3H6 +

3 O

2 ->

3 C

O +

3 H

2O

40 v

ol.-%

: sto

ichi

omet

ric

com

posi

tion

for

C3H

6 + 1

.5 O

2 ->

3 C

O +

3 H

2

Example for Propene/O2-mixtures:


Example: Detonative pressure pulses Pdet acting on the wall of a 20 l sphere in case of Propene/O2/N2, Pinitial = 5 bar abs, Tinitial = 25°C

Pressure at border line ofdetonative range about factor6 to 17 larger than in centerbecause of precompression.

The highest value attainableby Pdet/Pinitial is about 1300 !!

barabsbarabsP 203975.125.210110205

4.1)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−

0 10 20 30 40 50 60 70 80 90 100Propene C H [Vol.-%]3 6

0

10

20

30

40

50

60

70

80

90

100

O [Vol.-%

]

2

0

10

20

30

40

50

60

70

80

90

100

N

[Vol

.-%]

2


range of detonative

explosion

stoich

iometric

CH + 1.5

O -> 3 CO + 3

H

36

2

2

stoich

iometr

ic C

H +

3 O ->

3 CO +

3 HO

36

2

2

stoich

iometr

ic C

H +

4.5 O

-> 3

CO +

3 H

O

36

2

2

2


barabarabsP 669275.125.220120405

4.1)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−

barabsbarabsP 495125.2111445

4.1)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−

barabsbarabsP 332075.125.213113275

4.1)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−


4.1)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−


4.1)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−

barabsbarabsP 385125.21.1

11.13254.1

)14.1(

det =⋅⋅⎟⎠⎞

⎜⎝⎛⋅⋅⋅=

−


Summary concerning pressure load

The „obscure“ effects talked about in non-public communication seem to beexplainable with precompression

Pressure at the border line of detonative range about factor 6 to 17 larger than in center because of precompression!(I.e. in the detonative regime the lowest pressure load on the wall isgenerated by mixtures in the vicinitiy of the stoichiometric combustible/O2-mixtures)

Since in the empty vessel the static equivalent pressure Pstat of thedetonative pressure pulse Pdet is at least 0.5*Pdet, the lower limit for therequired pressure resistance of a detonation pressure proof empty vessel isknown. Since this lower limit is extremely high,it is questionable whether the designof a detonation pressure proof empty vessel is economically justifiable.

Pressures acting on the wall may be a factor 1300 higher than the initialpressure in the mixture. The main reason is that in vessels the highesttheoretically possible precompression factors (=deflagration pressure ratios) actually do occur !!



Introduction







Vessels used for the experiments

100 l vessel: L = 1309 mm; φi = 327.2 mm; L/ φi =4.0; distance P1-P3 = 1343 mm

500 l vessel: L = 2146 mm; φi = 570 mm; L/ φi =3.76; distance P1-P3 = 2309 mm

2500 l vessel: L = 3644 mm; φi = 956 mm; L/ φi =3.8; distance P1-P3 = 3866 mm

Characteristic parameters of all vessels:

Sketch of 2500 l vessel (the others are alike, only smaller):

s = 34 wal

l th

ickn

ess

s =

30

346

175

4021

3040 (cylindirical section)3718

s = 40

332128

3866

P2

1938

loca

tion

of ig

nitio

nw

eld

neck

flan

geN

W15

0, P

N16

0

wel

d ne

ck fl

ange

NW

300,

PN

160

torospheri-cal head

torospheri-cal head

oute

r dia

met

er φ

o = 1

016

inne

r dia

met

er φ

i = 9

56

1928

P1 P3L = 3644


Examples for pressure/time recordings by sensor P3 in 100 l and 500 l vessel

65 70 75 80 85 900

100

200

300

400

500

Time [ms]

Pres

sure

[bar

abs

]

File: EFOV108K.DAT

Experiment:Ethane=22.2 vol.-%, O2=77.8 vol-%, Pinitial = 5 bar abs,Tinitial = 25 °C,100 l vessel, L/D = 4

v = Δs/Δt = (2*1.343m)/2 ms = 1343 m/s

Δt = 2ms

65 70 75 80 85 900

250

500

750

1000

Time [ms]

Pres

sure

[bar

abs

]

File: EFOV150K.DAT

Experiment:Ethane=11.4 vol.-%, O2=40 vol.-%, N2=48.6 vol.-%,Pinitial = 8 bar abs,Tinitial = 25 °C,500 l vessel, L/D = 3.8Δt = 3.66ms

v = Δs/Δt = (2*2.309m)/3.66ms = 1261m/s

The peaks are due to the shockwave of the detonation which after having reached the one end of the vessel is reflected backwards into the hot reaction gas, travels until reaching the opposite torospherical head of the vessel, is again reflected and so on


Results of tests with stoichiometric Ethane/O2/N2-mixtures in vessels ranging from 20 l to 2500 l

heat explosion35

detonativedetonative40

deflagrativedeflagrative30

2500 l cylinder, L/D=3.8

20 l sphere

course of explosionO2-conc. in stoichiometricmixture [vol.-%]

detonative

deflagrative

500 l cylinder, L/D=3.76

detonative35

detonativedetonative40

deflagrativedeflagrative30

100 l cylinder, L/D=4

20 l sphere

course of explosionO2-conc. in stoichiometricmixture [vol.-%]

Tests with Pinitial = 8 bar abs

Tests with Pinitial = 4 bar abs


Summary of comparison of explosive regimes of combustible/O2/N2 mixtures in vessels of different volume

For stoichiometric mixtures there is - within experimental accuracy -no change in the critical composition (transition from deflagrative to detonative combustion) when varying the vessel volume over twoorders of magnitude !!!

For combustible/O2 mixtures the potential change of the criticalcompositions with vessel volume could not yet be studied.



Introduction







Experimental setup to determine predetonation distancesof Propene/O2-mixtures in a φi = 76.3 mm pipe at pinitial = 5 bar abs, 25°C

location ofthermal ignitionsource

2000 2000 2000 1000

(the lengths of the tube segments are specified as from centre of gasket to centre of gasket,i. e. the actual tubes are slightly less than 1000 mm or 2000 mm, respectively)

7000 mm, PN160, DN80, = 88.9 mm, = 76.3 mm, s = 6.3 mmφ φo i


Position of pressure sensors in the φi = 76.3 mm pipe

P10 P11 P12 P13 P14 P15 P16250

500 750

1000 1250

1500 1750

2000

P17

1000

2000

P17

1000

2000

P1

100

P2 P3 P4 P5 P6 P7 P8 P9

200 300

400

100 100 100 100 100

1000

location ofthermal ignition source

P10 P11 P12 P13 P14 P15 P16250

500 750

1000 1250

1500 1750

2000

P1

100

P2 P3 P4 P5 P6 P7 P8 P9

200 300

400

100 100 100 100 100

1000


Enlarged section of first two pipe segments:

Pressure sensors used (all piezoelectric, supplied by PCB):PCB M112A05, 0 - 345 bar, ca. 16 pC/barPCB M113A03, 0 - 1034 bar, ca. 5 pC/barPCB M119A11, 0 - 5520 bar, ca. 3.6 pC/bar


Predetonation distances of Propene/O2 in a φi = 76.3 mm pipe at 5 bar abs, 20 °C

Note: in 7 m long pipe with φi = 76.3 mm no DDT for Propene conc. ≤4 vol.-% (i.e. predet.distance > L/D=92)in 11 m long pipe with φi = 86 mm no DDT for Propene conc. ≥50 vol.-% (i.e. predet.distance > L/D=127)

Propene concentration in Propene/O2-mixture [vol.-%]0 10 15 20 25 3530 40 45 505

DDT deflagrationCourse of explosion in 20 l sphere, φi = 340 mm:

defl.heat expl. (?)

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45 50Propene concentration in Propene/O2- mixture [vol.-%]

Pred

eton

atio

n di

stan

ce

[leng

th/d

iam

eter

]

Predetonation distances of Propene/O2at 5 bar abs, 20°C; in 7 m long tube,76.3 mm internal diameter.

18.1

8 vo

l.-%

is s

toic

hiom

etric

for C

O2

and

H2O

form

atio

n

25 v

ol.-%

is s

toic

hiom

etric

for C

O a

nd H

2O fo

rmat

ion


Predetonation distances of stoichiometric Propene/O2/N2 in a φi = 76.3 mm pipe at 5 bar abs, 20 °C

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Propene concentration in stoich. Propene/O2/N2- mixture [vol.-%]

Pred

eton

atio

n di

stan

ce [l

engt

h/di

amet

er]

Predetonation distances of stoich. Propene/O2/N2(for CO2- and H2O-formation) at 5 bar abs, 20°C;in 7 m long tube, 76.3 mm internal diameter.

Propene concentration in stoichiometric Propene/O2-mixture [vol.-%]

DDTdeflagrationCourse of explosion in 20 l sphere, φi = 340 mm:

heat expl. (?)

0 4 6 8 10 1412 16 18 202 3 5 7 9 1311 15 17 191


Example for how to determine the predetonation distance in pipes from pressure/time diagramsExample: Propene/O2, 5 bar abs, 20 °C, 41 vol.-% Propene, φi=76 mm, L = 7 m, ignition at t = 0 ms

11 11.5 12 12.5 13 13.5 140

50100150200

500 mm

11 11.5 12 12.5 13 13.5 140

50100150200

800 mm

11 11.5 12 12.5 13 13.5 140

50100150200250300

1250 mm

11 11.5 12 12.5 13 13.5 140

100200300 1500 mm

11 11.5 12 12.5 13 13.5 140

200400600800

1750 mm

11 11.5 12 12.5 13 13.5 140

200400600800

2000 mm

11 11.5 12 12.5 13 13.5 140

100200300400

Time [ms]

6000 mm

pressure sensor defect

v = s/ t=4.25m/1.64ms=2591m/sΔ Δ

v = s/ t=0.25m/0.1ms=2500m/sΔ Δ

reto

natio

n pe

ak p

ropa

gatin

g ba

ckw

ards

Pre

ssur

e[b

ar a

bs]

Predetonation distance is given byintersection of distance-time curve of retonation and detonation wave. (in this example: Lpredet = 1560±50 mm)

P3 P4 P5 P6 P7P1 P2


1250 500 800 1500 1750 2000 6000 5000 4000 7000 1000

11,5

11,75

12

12,25

12,5

12,75

13

13,25

13,5

0 1000 2000 3000 4000 5000 6000 7000Distance of pressure sensor from ignition source (left blind flange) [mm]

Tim

e of

arr

ival

of r

eton

atio

n or

det

onat

ion

wav

e [m

s]

Detonation wave, v = 2591 m/s

Retonation wave, v = 1612 m/s


Clarification of an apparent contradiction with respectto predetonation distances

Lean mixtures that require up to 760 mm (L/D ≅ 10) predetonation distance in a pipe andrich mixtures that require up to 1500 mm (L/D ≅ 20) predetonation distance in a pipe

manage to run up to detonation in a sphere with radius 170 mm !!!

Possible reasons that mixture detonates in sphere although in pipe lpredet >> radius of sphere:- In the sphere there is massive precompression (up to factor of 12 on lean side and up to a factor of 20 on rich side of detonative range) which is absent in long pipes. Predetonation distances reduce with increasing pressure (see next slide).

- In sphere sonic pressure waves of initial deflagration are reflected backwards and interfere with combustion zone, which might accelerate the flame. In long pipes this effectshould almost be absent.

At first glance this is an unexpected result: In the pipe the unburnt gas is made stream turbulent between rigid walls by expansion of thereaction products. This should encourage flame acceleration.Hence, if for some mixture the predetonation distance in a pipe is larger than the radius of thesphere, one would not expect this mixture to run up to detonation in the sphere.

- Because precompression in the sphere is adiabatic, the temperature of the mixture risessubstantially (see next slide). Possibly this also contributes to reducing the predetonationdistance (????)

- Based on the precompression difference between lean and rich side it qualitatively makessense that on the rich side mixtures which exhibit about twice the predetonation distance in a pipe as mixtures on the lean side, still run up to detonation in the sphere


Predetonation distances as function of initial pressure

1 10

0.1

1

initial pressure P [bar abs]initial

pred

eton

atio

n di

stan

ce s

[m]

D5

2

3

0.5

0.2

0.3

0.05

0.03

m = 0.43

m = 0.50

m = 0.61

m = 0.76

502 30203 50.2 0.3 0.5

H + N O, 38 °C, = 79 mm

2

2

iφ

H + O , 37.7 °C, = 15 mm

2

2

iφ

m = 0.76

H + O , 200 °C, = 15 mm

2

2

iφ

C H + 4 O

, 37.7 °C, = 15 mm

22

2

iφ

CH + 5.67 O , 40 °C = 15 mm

4

2

iφ

2 CO + O , 40 °C, = 15 mm

2

iφ

m = 1

m = 0.057C H + air, 20 °C, stoichiom., = 50 mm

2 4iφ

s = D

const.(P )ini

m

Empirical law for thepressure dependence of the predetonation distance:

H + O , 200 °C, = 15 mm, L = 2.94 m 2 2 iφ

H + O , 37.7 °C, = 15 mm, L = 2.94 m 2 2 iφ

H + N O, 37.7 °C, = 79 mm , L = 2.94 m (L.E. Bollinger, J. A. Laughrey and R. Edse, American Rocket Society: ARS Journal (Easton, Pa) 32, p. 81 - 82 (1962)

2 2 iφ

CH + 5.67 O , 40 °C = 15 mm, L = 2.94 m 4 2 iφ

2 CO + O , 40 °C, = 15 mm, L = 2.94 m 2 iφ

C H + 4 O , 37.7 °C, = 15 mm, L = 2.94 m 2 2 2 iφ

L.E. Bollinger, M. C. Fong and R. Edse, American Rocket Society: ARS Journal (Easton, Pa) 31, p. 588 - 595 (1961) }

C H + air, 20 °C, stoichiom., = 50 mm, L = 22 m (I. Ginsburg and W. L. Bulkley, Chemical Engineering Progress, Vol. 59, no. 2, p. 82 - 86 (1963)

2 4 iφ



152,3299,0462,0638,250

148,2289,0444,3611,245

143,7278,1425,1582,040

138,7266,0403,9550,035

133,0252,3380,3514,530

126,3236,6353,4474,525

118,3218,0321,9428,420

114,6209,4307,6407,618

110,4200,0292,1385,016

105,8189,6274,9360,414

100,5177,9255,8333,112

94,4164,4234,0302,310

87,0148,4208,5266,88

77,7128,7177,6224,26

65,0102,5137,3169,84

44,461,576,790,32

36,245,854,261,61,5

30,034,237,840,91,2

γ = 1,1γ = 1,2γ = 1,3γ = 1,4



( )γ

γ 1−

⎟⎠⎞

⎜⎝⎛⋅=

initialfinal

initialfinal pp

TTFormula for temperature increase due to adiabatic compression:

402,0634,9893,61173,450

395,6619,1865,61130,545

388,5601,7835,11084,040

380,5582,5801,41033,235

371,4560,8763,9977,030

360,8535,8721,2913,525

348,1506,3671,3840,220

342,1492,7648,6807,218

335,6477,8623,9771,516

328,2461,3596,7732,414

319,9442,7566,3689,112

310,1421,3531,7640,210

298,4395,9491,3583,88

283,7364,6442,2516,26

263,5322,9378,3429,94

230,8257,9282,0303,62

217,8233,1246,4258,11,5

207,9214,6220,3225,31,2

γ = 1,1γ = 1,2γ = 1,3γ = 1,4




Summary on predetonation distances of Propene/O2

Predetonation distances change drastically (about 2 orders of magnitude) over a relatively narrow range of compositions

Above statements are compatible with the well establishedobservation that combustible/air mixtures do not run up to detonationin empty vessels ->>>> see next slide ->>>>>

Above result corroborates the so far preliminary conclusion drawnfrom the comparisons of the detonative regimes found in 20, 100, 500 and 2500 l vessels (detonative range in 20 l sphere about thesame as in 2500 l vessel)


Tentative generalisation of the results found for the course of theexplosion of Propene/O2/N2 in the 20 l sphere and in tubes (thermal ignition presumed!)

0 10 20 30 40 50 60 70 80 90 100Propene C H [Vol.-%]3 6

0

10

20

30

40

50

60

70

80

90

100

O [Vol.-%

]

2

0

10

20

30

40

50

60

70

80

90

100

N

[Vol

.-%]

2


range of detonative

explosion

stoich

iometr

ic CH + 1.5

O ->

3 CO + 3 H

36

2

2

stoich

iometr

ic C

H +

3 O ->

3 CO +

3 HO

36

2

2

stoich

iometr

ic C

H +

4.5 O

-> 3

CO +

3 H

O

36

2

2

2


4.5 vol.-% Propenein Propene/O2

45 vol.-% Propenein Propene/O2

4.46 vol.-% Propenein Propene/air(stoichiometric)

L/D = 64

L/D = 70

L/D ca. 100(typical for

stoichiometrichydrocarbon/air)

Combustible/air-mixturesdo not detonate in vesselsof any practical size.

Propene/O2 mixtures withpredetonation distances L/D ≥ 100 do not detonate in 20 l vessel

Detonative range in larger vesselsseems to be about the same as in 20 l vessel

Predetonation distance of combustible/air-mixturesis about L/D ≥100

Propene/O2-mixtures withL/D ≥ 100 do not detonate in vessels of any practical size

Combustible air mixtures withL/D ≥ 100 do not detonate in vessels of any practical size

+

=

+

=



Introduction







Did our the ignition source directly trigger a spherical detonation?

Ignition source used is fusing wire according to EN 1839, section 4.2.3.3.3 :

- wire of 0.2 mm diameter, ca. 5 mm long, clamped between two electrodes

- by a thyristor the wire is connected for a fraction of a half wave withthe secondary coil of an insulation transformer(thyristor typically opens between 0° and 150° and closes at 180°)

- wire melts in about first millisecond

- just when first contact breaks apart between the electrodes by the melting of the wirean arc discharge emerges and keeps on burning until the voltage between the pole tips falls back to 0.

This ignition source must be rated as purely thermal, since the shock waveassociated with the first occurrence of the arc discharge is negligible (seenext slides)


Current/time, Voltage/time and Pressure/time diagrams of ignitionsource „melting wire with subsequent arc discharge“ (1/5)

-3 -2 -1 0 1 2 3 4 5 6 70.850.9

0.951

1.051.1

1.15

Pres

sure

[bar

abs

]

File: v001_hwz-1_zw120°_1bar-n2.sbs

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Time [ms]

Pressure at sensor in 1 cm distance of arc discharge

Current through wire and current of arc discharge

Voltage at output pin of Halbwellenzuendgeraet (about factor 7 larger than at electrode tips)

Cur

rent

[A]

Volta

ge [V

]

Example:ignited in 1 bar N2at 20°C, thyristor switched on from 120° to 180°of one half cycleof mains supply

Heating of wire untilmelting occurs

Arc dischargeis burning

Thyristor opens for 3.33 ms (120°-180° of one half wave of 50 Hz mains supply)

In about 50% of all ignitions conducted1 bar N2 at 20°C there was not at all any pressuredetected by thepiezoelectric sensor(irrespective of theduration the thyristorwas switched on)



-3 -2 -1 0 1 2 3 4 5 6 7 80.85

0.90.95

11.05

1.11.15

Pres

sure

[bar

abs

]


-3 -2 -1 0 1 2 3 4 5 6 7 80

100

200

300

-3 -2 -1 0 1 2 3 4 5 6 7 80

100

200

300

Time [ms]

Cur

rent

[A]

Volta

ge [V

]Pressure at sensor in 1 cm distance of arc discharge



Example: ignited in 1 bar N2 at 20°C, thyristor switched on from 5° to 180° of one half cycle of mains supply



-3 -2 -1 0 1 2 3 4 5 6 719.5

19.75

20

20.25

20.5P

ress

ure

[bar

abs

]


-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Time [ms]




Cur

rent

[A]

Volta

ge [V

]


For all ignitionsconducted at 20 bar N2and at 20°C there was a pressure signaldetected by thepiezoelectric sensor of the order of Δp = ±0.4 to ±0.7 bar


Current/time, Voltage/time and Pressure/time diagrams of ignition source„melting wire with subsequent arc discharge“ (4/5)

-3 -2 -1 0 1 2 3 4 5 6 719.5

19.75

20

20.25

20.5Pr

essu

re [b

ar a

bs]


-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Cur

rent

[A]

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Time [ms]

Volta

ge [V

]







-3 -2 -1 0 1 2 3 4 5 6 719.5

19.75

20

20.25

20.5

Pre

ssur

e [b

ar a

bs]


-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Time [ms]




Cur

rent

[A]

Volta

ge [V

]

-3 -2 -1 0 1 2 3 4 5 6 719.5

19.75

20

20.25

20.5

Pres

sure

[bar

abs

]


-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Cur

rent

[A]

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Time [ms]

Volta

ge [V

]




-3 -2 -1 0 1 2 3 4 5 6 70.850.9

0.951

1.051.1

1.15

Pres

sure

[bar

abs

]


-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

-3 -2 -1 0 1 2 3 4 5 6 70

100

200

300

Time [ms]




Cur

rent

[A]

Volta

ge [V

]

-3 -2 -1 0 1 2 3 4 5 6 7 80.85

0.90.95

11.05

1.11.15

Pres

sure

[bar

abs

]


-3 -2 -1 0 1 2 3 4 5 6 7 80

100

200

300

-3 -2 -1 0 1 2 3 4 5 6 7 80

100

200

300

Time [ms]

Cur

rent

[A]

Volta

ge [V

]




1 ba

r N2,

120°

-180

°1

bar N

2, 5°

-180

°

20 b

ar N

2, 12

0°-1

80°

20 b

ar N

2, 5°

-180

°


Summary of talk

Detonative range in empty vessels is determined

Abundant set of explosion characteristics in the importantbut so far mostly unexplored combustible/air/O2 region of the explosive range

Pressure load on the wall is understood quantitatively

The link between detonation in pipes and in vessels isestablished

Explosions in Methane O2 N2 Mixtures in Vessels

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Transcript of Explosions in Methane O2 N2 Mixtures in Vessels