self-ignition of hydrogen-nitrogen mixtures during high-pressure … · 2018. 10. 24. · projekt...

Projekt współfinansowany ze środków Unii Europejskiej w ramach Europejskiego Funduszu Społecznego.

Self-ignition of hydrogen-nitrogen mixtures duringhigh-pressure release into air

Rudy W.1*, Teodorczyk A.1, Wen J.X.2

Europejskiego Funduszu Społecznego.1 Warsaw University of Technology, Institute of Heat Engineering, Warsaw, Poland

2 University of Warwick, School of Engineering, Coventry, UK

*[email protected]

International Conference on Hydrogen Safety, Yokohama, Japan

19.10.2015

Presentation plan

1. Introduction

2. Experimental stand and procedure

3. Results

4. Numerical simulations

5. Results

6. Conclusions

Rudy et al. Self-ignition of hydrogen-nitrogen mixtures during high-pressure release into air ICHS 2015 2

1. Introduction

Hydrogen ignition without distinct ignition source:

1922 - Anon

1930 - Fenning and Cotton

1965 - Reider et al.

1972 - Wolanski and Wojcicki, ‘diffusive ignition model’

Recent research in hydrogen ‘self-ignition’ process:

- Pure hydrogen release,

Various geometrical configurations and boundary conditions:

• Extension channel length

• Extension channel cross-section shape (round, rectangle)


• Extension channel cross-section shape (round, rectangle)

• Extension channel material (metal, glass)

• Diaphragm: material, opening rate, initial curvature

• Obstacle presence in the front of the hydrogen stream

- Shorter tubes <40 mm lead to significant increase in Pburst

- High discrepancies observed due to the different experimentalstands and procedures utilized:

• fast valves/slow filling

• diaphragm burst/’tulip shape’ opened/punctured

Little data regarding gas doping influence on self-ignition process.

Control and data acquisition section: computer, amplifier, time unit,

PCB pressure sensors, ion probes, ionisation probes

Air section

1x0.11x0.11 m tube with optical access, diaphragm holder and

extension tube

High-pressure section

gas cylinders, single acting gas-driven booster – Haskel AG-75,

high-pressure line, pressure accumulator, fast acting

electromagnetic valve

Diaphragms made of aluminium,

Thickness: 0.1, 0.15, 0.2, 0.25 mm

2. Experimental stand and procedure


Thickness: 0.1, 0.15, 0.2, 0.25 mm

Sensors positions regarding diaphragm and flow direction

(PS – pressure sensors, IP – ion probes, PD – photodiodes):

•PS1 – 30 mm upstream,

•PS2 – 60 mm downstream,

•PS3 – 860 mm downstream,

•IP1 – 360 mm downstream,

•IP2 – 560 mm downstream,

•PD1 – 100 mm downstream,

•PD2 – 125 mm downstream,

•PD3 – 150 mm downstream.

2. Experimental stand and procedure cont.

Rudy et al. Self-ignition of hydrogen-nitrogen mixtures during high-pressure release into air ICHS 2015

d = 6 mm d = 10 mm d = 14 mm

5

30 ms signal

2. Experimental stand and procedure cont.


Total number of experiments 655:

H2

– 360

H2+N

2:

5% N2

- 213

10% N2

- 82

Extension tubes:

d = 6, 10 and 14 mm,

L = 10, 25, 40, 50, 75, 100 mm,

Initial pressure range

3. Results


Initial pressure range

2 - 18 Mpa

Initial temperature:

ambient ~298 K

7

100% H2

H2+ 5% CH

4H

2 + 10% CH

4H

2 + 5% N

2 H

2 + 10% N

2

W. Rudy, A. Dabkowski, A. Teodorczyk, Experimental and numerical study on spontaneous

ignition of hydrogen and hydrogen-methane jets in air, International Journal of Hydrogen

Energy, Vol. 39, Issue 35, 2014, pp.20388-20395,

3. Results cont.


with ignition without ignition

Pburst = 9.76 MPa Pburst = 9.77 MPa

- pressure drop in PS1 sensor – diaphragm burst- clear photodiodes signals when gas leaving the tube – ignition in extension tube- ionisation probes signals � sustained combustion in the further part of the tube- pressure sensors PS2 and PS3 higher indications due to the combustion- PS2 and PS3 oscillations – shock reflections

8

100% H2

3. Results cont.


- Self-ignition is possible only above certain burst pressure

- ‘Ignition limit’ – minimum initial pressure for which ignition was observed

- Ignition limit decreases with extension channel length increase

- No ignition for extension channels with L < 40 mm � non-linear dependence observed previously

9

3. Results cont.


H2 + N2 H2 + CH4

3. Results cont.


5% N2

10% N2

d →

L ↓ 6 mm 10 mm 14 mm 6 mm 10 mm 14 mm

100 mm 1.4 2.08 2.12 1.87 2.85 2.72

75 mm 1.25 1.21 1.33 1.83 1.83 1.81

50 mm 1.19 1.39 1.15 - - -

40 mm 1.14 1.34 1.15 - - -

W. Rudy, A. Dabkowski, A. Teodorczyk, Experimental and

numerical study on spontaneous ignition of hydrogen and

hydrogen-methane jets in air, International Journal of Hydrogen

Energy, Vol. 39, Issue 35, 2014, pp.20388-20395,

Ignition limit points compared to the postshock conditions (Cantera calculations)

Postshock P2, T2 as a function of driver gas composition and pressure

3. Results cont.


Results scatter shows that ideal shock assumptions do not include real 3-dimensional effects of therelase including shock-shock, shock–wall interations and diaphragm opening process.

Higher postshock conditions required for ignition in shorted tubes (L= 40-50 mm)

None of the results is below the autoigntiion temperature of hydrogen-air mixture (T= 858 K).

Kiva3V

- ALE methodology

- Code substantially modified by Wen and co-workers, details in:

Xu et al. J.Loss Prev. Proc. Ind. 21, 2008 and 22, 2009,

Wen et al. Comb. Flame 156, 2009,

Xu et al. Int. J. Hydr. E. 36, 2011

Wen et al. ICHS 2013, Brussels, Belgium

- Selected part of experimental stand geometry

- Axisymmetrical domain

- Saxena and Williams’s reaction model (21 reactions)

- 1 200 000 cells

4. Numerical simulations


- 1 200 000 cells

- Structural mesh in extension tube - 15 µm

- Orthogonal mesh in high-pressure part of the domain 15-150 µm

- Diaphragm 0.1 mm thick, opening time 5 µs

Pburst

[MPa] 100% H2

5% N2

10% N2

5 X

6 X X

8 X X X

10 X X X

12 X

kj 5.0 cm

5. Results


100% H2, Pburst = 6 MPa, frames every 5 µs starting from 1 µs of

simulation time, first ignition near wall after 16 µsinstabilities K.-H. i R.-T.

P = 5 MPa, τ = 40 µs

P = 6 MPa, τ = 40 µs

P = 8 MPa, τ = 36 µs

100% H2 cases for contact surface position near tube end

5. Results cont.


Increase in the mixing intensity at the contact surface due to the stronger leading shock

influence. Number of ignition spots:

5 MPa – 1 at the wall

6 MPa – 2 at the wall

8 MPa – 3: 2 at the wall, 1 in the channel axis

10 MPa – 3: 2 at the wall, 1 in the channel axis

P = 10 MPa, τ = 34 µs

Maximum temperatures recorded during simulations

5. Results cont.


100% H2 H2 + 5% N2 H2 + 10% N2

- First temperature peak at 5µs time – diaphragm fully open,

- Progressive temperature increase due to the shock waves reflections

- Higher nitrogen addition and lower initial pressure delay first ignition event

5. Results cont.

Simulation Experiment


Ignition and following sustained combustion requires at least 3 ignition spots. Reaction should spread

to the whole contact surface before leaving the tube which is consistent with previously done research

(Lee et al. 2011, Kim et al. 2013, Grune et al. 2013)

2.5 cm

0.0 µs 2.5 µs 5.0 µs 10.0 µs 20.0 µs

5. Results cont.

Vshock

~ 1350 m/s

Vtheor

= 1360 m/s

Vshock

~ 1315 m/s Vshock

~ 1240 m/s Vshock

~ 1084 m/s Vshock

~ 890 m/s

Diaphragm opening time influence


Pburst = 6 MPa, 100% H2

0 µs – ideal case, shock velocity close to

theoretical value

• finite opening process provides shock waves

reflections which enhance mixing due to the

instabilities generated at the multi-shocked

contact surface

• Increase in opening time influences initial

shock wave structure and initial shock velocity

Frames spaced each 2 µs starting from 1 µs

6. Comclusions

• Experimental and numerical research on H2

and H2-N

2mixtures self-ignition process

during release into air was presented

• In total, 295 experiments were conducted for H2+N

2mixtures (+360 for pure H

2)

• Self-ignition process highly depends on the extension tube length, initial pressure and

mixture composition

• N2

addition considerably increases the mixture’s initial pressure necessary for the self-

ignition to occur, effect is stronger for longer tubes and may increse pressure as much

as 2.12 or 2.85-times for 5% and 10% of N2

in the mixture with H2

respectively


• KIVA-3V simulations showed that depending on the initial pressure of the mixture,

specific ignition sequence is present with 1, 2 or 3 ignition spots at various locations

• 1st and 2nd ignition spots are present in the vicinity of the extension channel wall

• 3rd ignition spot is present at the tip region of the contact surface

• N2

addition ‘shifts’ the initial pressure necessary for the ignition sequence to occur

• Comparison with experimental results pointed at condition for 3 ignition spots

presence for sustained combustion after leaving the tube

• Diaphragm opening time highly influences initial shocks structure and shock velocity,

thus instabilities generated at the contact surface

Acknowledgements

This work has been financially supported by the European Union in the framework of European Social Fund through the “Didactic Development Program of the Faculty of

Power and Aeronautical Engineering of the Warsaw University of Technology”


Thank you for your attention!


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