Pure Hydrogen Jet Flames

Wu, Y., International Conference on Hydrogen Safety, 11-13 September 2007. 1

Prediction of the Lift-off, Blow-out and Blow-off Stability Limits of Pure Hydrogen and

Hydrogen/Hydrocarbon Mixture Jet Flames

Wu, Y., Al-Rahbi, I. S., Lu, Y

Department of Chemical and Process Engineering, Sheffield University

Kalghatgi, G. T.

Shell Global Solutions (UK), Chester CH1 3SH, UK


1. Experimental study on the liftoff and blowout stability of pure hydrogen, hydrogen/propane and hydrogen/methane jet flames using a 2 mm burner.

2. Carbon dioxide and Argon gas were used in the study for the comparison with hydrocarbon fuels.

3. The non-dimensional analysis of liftoff height approach was used to correlate liftoff data of H2, H2-C3H8, H2-CO2 , C3H8 and H2-Ar jet flames.


Pure Hydrogen Jet Flames

Attached Flame Lifted Flame


H2/CO2 Flames



Hydrogen/propane Jet Flames



Stability of Pure Hydrogen Jet Flames

0

5

10

15

20

25

30

35

500 700 900 1100 1300 1500

Jet exit velocity [m/s]

Lift

-off

he

igh

t [m

m]

Present study 1 (2mm)



Kalghatgi(1984)'s data (1.74mm)

Cheng and Chiou (1998)'s data (2.9mm)

Cheng and Chiou (1998)'s data (1.8mm)

Trend Line for Kalghatgi (1984)'s data (1.74mm)

Comparison of experimental measured lift-off height of pure hydrogen jet flames.


Lift-off Height

0

10

20

30

40

50

60

70

80

400 600 800 1000 1200 1400 1600

Jet exit velocity (m/s)

Lif

toff

hei

gh

t (

mm

)

H2H2+CO2H2+C3H8H2+CH4

Comparison of the lift-off height of H2/C3H8, H2/CH4 and H2/CO2 flames


Lift-off Velocity

0. 0

100. 0

200. 0

300. 0

400. 0

500. 0

600. 0

700. 0

800. 0

0. 0 5. 0 10. 0 15. 0 20. 0

Diluent concentration [%]

Liftoff velocity

[m/s]

H2+C3H8

H2+CH4

Comparison of liftoff velocity H2/C3H8 and H2/CH4 flames


Blow-out and Blow-off Velocity

0

200

400

600

800

1000

1200

1400

0 10 20 30 40 50 60 70

Dilutant concentration (%)

Blo

wou

t/Blo

wof

f Vel

ocity

(m

/s)

H2+C3H8 Bl owout

H2+CO2 Bl owoff

H2+CO2 bl owout

H2+CH4 Bl owoff

Comparison of blow-out and blow-off velocity of H2/C3H8, H2/CH4 and H2/CO2 flames


H2-C3H8 Jet Flames

C3H8 addition to attached H2 flames always produced lifted flames, and blow-out occurred at high jet velocities.

C3H8 addition to lifted H2 flames increased the lift-off height by nearly 2.6 times.

The blow-out occurred at C3H8 concentration of around 4 to 5 %.


H2-CO2 and H2-Ar Jet Flames

Two flame stability regimes were identified.

When CO2 ≥ 6.4 %, a stable attached flame was produced and leading to direct blow off at high velocities.

When CO2 ≤ 6.4 %, a lifted flame was produced and then blow-out at higher velocities.

CO2 addition increased the liftoff height by nearly two times.

Argon behaved in a similar way to CO2 .


H2-CH4 Jet Flames

The effects of CH4 addition were different from C3H8 addition. Similar to the effect of CO2 addition, there were two flame stability regimes when CH4 was added into initial attached hydrogen jet flames.

When the CH4 ≥ 20%, flame would remain attached until blow-off at high velocity.

If the CH4 ≤ 20%, CH4 addition to an initial attached hydrogen jet flame can produce lifted flame. However the blowout flame conditions were not observed.


Laminar Burning Velocity

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50

100

150

200

250

300

350

0 20 40 60 80 100 120

Diluent concentration (% vol)

Lam

inar

bur

ning

vel

ocity

Su

(cm

/s)

Hydrogen+Carbon Dioxide

Hydrogen+Propane

Hydrogen+Methane

The laminar burning velocity of H2/C3H8, H2/CH4 and H2/CO2 flames



The reported values of laminar flame velocity of hydrogen flames are scattered in the range 370 cm/s to 250 cm/s. The discrepancy was mainly due to whether and how the effect of stretch rate over the laminar flame velocity for the spherically expanding flames was taken into account.



The liftoff process of H2-C3H8 , H2-CH4 and H2-CO2 jet flames was strongly influenced by the chemical kinetics. Hydrocarbon acted as a sink for the active radicals that are of importance in the combustion chemistry of H2. The hydrocarbon is the dominant element in determining the burning velocity of hydrogen hydrocarbon mixtures.


Assessment of Empirical Correlations

Non-dimensional analysis of lift-off height

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2000

4000

6000

8000

10000

0 40 80 120 160 200 240

Ue/Su * (Jet density / air density)

Re S

u

H2; 2 mm burner

C3H8; 2 mm burner

H2/CO2; 2 mm burner

C3H8-H2; 2 mm burner

H2/Ar; 2 mm burner

H2-CH4; 2mm burner


Comparison of measured hydrogen liftoff height and predictions using correlations.

0

5

10

15

20

25

30

35

40

500 600 700 800 900 1000 1100 1200

Jet exit velocity [m/s]

Lift-

off h

eigh

t [m

m]

Using Kalghatgi'scorrelation

Using Miake-Ley &Hammer correlation

Measured in presentstudy


Conclusions

The flame liftoff height of the pure H2 jet diffusion flame was found to increase with the jet velocity. Agreement with previously published correlations was found to depend on the value used for the maximum laminar burning velocity of H2.


Conclusions

Addition of C3H8 to hydrogen required least liftoff velocity and produced highest liftoff height among three additive gases. C3H8 is most effective in producing lifted flames.

C3H8 addition is more effective in blowout of a hydrogen flame than CO2 addition.

The effects of methane on the hydrogen flame were different from the ones of propane and had similarities to the ones of carbon dioxide. At high concentration, direct blowoff of the methane/hydrogen was observed.


Conclusions

Using non-dimensional analysis of liftoff height approach, the experimental data can be fitted into a single line with a slope of 48. The uncertainty using this approach is the value of the maximum laminar flame velocity of hydrogen flames.


Thank you !

Pure Hydrogen Jet Flames

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