Combustion Limits in Fire and Explosion Hazards

Geoff Chamberlain and Jonathan Puttock, Major Hazards Management

Team, Shell Global solutions UK, Chester.

CONFIDENTIAL

Early Experiments – G. Kalghatgi, 1981• Determined the blow out limits for

subsonic gases.• Established universal stability curve.

Experimental results – Mach No. v burner diameter

q q

q

Flame stability in still air – natural gas Flame stability correlation and blow-out data

0

10

20

30

40

50

60

70

80

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

Hole diameter, m

Blow-out data

Correlation for natural gas

unstable flames

5.11.1 /0028.0/ airjHuj RSu

Experiments in crosswinds – lifted flames• Sheffield University wind tunnel at Buxton• Burners 2-20 mm, crosswinds up to 8m/s• Methane, propane, Butagas (propane/butane

mix), ethylene• Results non-dimensionalised using the grouping

• Flames are less stable when burner tilted away from wind

Su ( RH ) ( air/

j )1.5

Flame stability – lifted flames in crosswind Flame stability - lifted flames

correct H - GTK's data

-3

-2.8

-2.6

-2.4

-2.2

-2

-1.8

-1.6

-1.4

-1.2

-1

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

v*

u*

Methane Propane Ethylene Butagas

Video

Wake stabilised flames

The Universal Flame Stability Map

CONFIDENTIAL

-1

-2

-3

-4

-5

-6

0.0 0.002 0.004 0.006

L ifted F lames

V ortex S tablisedB oundary L ayer

S tab ilised

R im

S tab ilised

U nstable F lames

U ns table F lames

10

10

10

10

10

10

Sca

led

gas

velo

city

Scaled wind speed

Universal flame stability map

Uncertain boundary

Data boundary

Q = 1

only if Q

> 1

Wake stabilised flames – effect of burner tilt• Burner tilted away from flame, flame is

more stable – opposite effect with lifted flames.

Bradley et al – simulation heat release contours MW/m3. Jet mean velocity 20m/s, crosswind 5.5 m/s. 10mm diam.

CMC flamelet combustion model. HPCx Daresbury.q q

Bradley et al – simulation heat release contours and velocity vectors close to burner tip.

q q

q

Flammability Limits – Fuel/air/water vapour system. Flame extinction and oscillatory flames in compartments.

q q