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The determination of explosion indices of flammable gases is an important part of explosion prevention. Explosion indices could be influenced by initial temperature, initial pressure, humidity, ignition energy and others. This contribution deals with the effect of ignition energy size on explosion indices of flammable gases. For experimental measurements, three flammable gases were chosen—methane, propane and hydrogen. The paper introduces the measurement results of the gas explosion parameters at various sizes of the ignition energy using explosion autoclave VA-20. Conclusions include the evaluation of influence of the ignition energy size on particular explosion indices.
Faculty of Safety Engineering, VSB-Technical University of Ostrava, Lumirova, Ostrava-Vyskovice, Czech Republic
Petr Lepík
Faculty of Safety Engineering, VSB-Technical University of Ostrava, Lumirova, Ostrava-Vyskovice, Czech Republic
Jakub Melecha
Faculty of Safety Engineering, VSB-Technical University of Ostrava, Lumirova, Ostrava-Vyskovice, Czech Republic
*Address all correspondence to: miroslav.mynarz@vsb.cz
1. Introduction
The explosion could happen wherever fuel, oxygen and sufficient ignition source appear together. The ignition energy is really significant. An explosive mixture is not ignited unless energy of the ignition source is sufficient. The ignition energy with a value of 10 J is used by default for the determination of explosion parameters of gases and vapours of flammable liquids. If the mixture is not ignited under given experimental conditions, it does not mean necessarily that the examined mixture is not explosive. When a higher ignition energy is used, the mixture could be ignited and high explosion indices could be reached (Mynarz et al., 2012).
Besides ignition source—the standard (EN 1127-1, 2011) defines 13 groups of ignition sources—duration time also matters. The explosion range is more wide with increasing size of the ignition energy— the lower explosive limit (LEL) is decreasing and the upper explosive limit (UEL) is growing. Table 1 introduces the effect of the ignition energy on the methane explosive limits.
Ignition energy Ei (J)
LEL (vol.%)
UEL (vol.%)
Explosion range (vol.%)
1
4.9
13.8
8.9
10
4.6
14.2
9.6
100
4.3
15.1
10.8
10,000
3.6
17.5
13.9
Table 1.
The effect of the ignition energy on the explosive limits of methane-air mixture (SAFEKINEX, 2002).
Increasing ignition energy affects the explosive limits but also increases maximum explosion pressure and the maximum rate of explosion pressure. The effect of the ignition energy is significant especially at the rate of explosion pressure rise.
The most common ignition sources suitable for measurement of explosive limits and explosion indices are inductive spark, chemical (pyrotechnic) igniter and fuse wire. Efficiency of each mechanism is different; various results could be reached with the above-mentioned ignition sources. This is manifested by results of measurements of the effect of initial pressure on hydrogen explosive limits using nickel fuse wire and electric spark, see Figure 1.
Figure 1.
The effect of initial pressure on explosive limits with the use of nickel fuse wire and electric spark (Conrad and Kaulbars, 1995).
For experimental measurements of the effect of the ignition energy size on explosion indices, three samples of gases were chosen—methane, propane and hydrogen. Parameters of particular gases are shown in Table 2.
The explosion autoclave VA-20 was used for experimental measurement of the effect of the ignition energy size on gas explosion indices. The setup is made for determination of the explosion indices of dust, gases and hybrid mixtures. The volume of the experimental double-coat chamber is 20 L (Kuhner Safety). Figure 2 presents the scheme of the explosion autoclave VA–20.
Following chapters introduce the experimental results of measurement of explosion indices of methane, propane and hydrogen with air using the apparatus VA-20. The chemical igniter with ignition energies of 80, 160 and 240 J was used. The values of maximum explosion indices and lower explosive limit were determined in a range of minimum 0.5 vol.%.
4.1. Methane
Experimental results of the effect of the ignition energy on the explosion indices of methane are presented in Table 3 and Figures 3 and 4. Table 4 compares the maximum explosion pressure, maximum rate of explosion pressure rise and the lower explosive limit of methane for particular energies of ignition sources. Percentage changes related to the measurement with the lowest energy are also listed.
Figure 3.
Graph of explosion pressure depending on methane concentration for various ignition energies.
Figure 4.
Graph of rate of explosion pressure rise depending on methane concentration for various ignition energies
Comparison of maximum explosion indices of methane.
4.2. Propane
Table 5 and Figures 5 and 6 show experimental results of the effect of the ignition energy on the explosion indices of propane. Table 6 compares the maximum explosion pressure, maximum rate of explosion pressure rise and the lower explosive limit of propane for particular energies of ignition sources. Percentage changes related to the measurement with the lowest energy are also listed.
Figure 5.
Graph of explosion pressure depending on propane concentration for various ignition energies.
Figure 6.
Graph of rate of explosion pressure rise depending on propane concentration for various ignition energies.
Concentration (vol.%)
2
2.5
3
4
4.5
5
6
7
80 J
pm (bar)
0
4.8
6.0
7.8
8.1
7.9
7.2
5.6
(dp/dt)m (bar s−1)
0
47
122
262
290
234
125
36
160 J
pm (bar)
0
5.2
6.2
7.7
8.3
8.3
7.5
6.6
(dp/dt)m (bar s−1)
0
63
183
269
362
350
171
80
240 J
pm(bar)
0.1
0.1
6.2
7.7
8.2
8.2
7.6
6.7
(dp/dt)m (bar s−1)
0
5
22
342
374
329
238
121
Table 5.
Explosion indices of propane.
80 J
160 J
Propane percentage change (%)
240 J
Percentage change (%)
pm (bar)
8.2
8.3
1.2
8.2
0.0
(dp/dt)m(bar s−1)
305
366
20.0
377
23.6
KGmax (bar m s−1)
83
99
20.0
102
23.6
LEL (vol.%)
2.0
2.0
0.0
1.5
−25.0
Table 6.
Comparison of maximum explosion indices of propane.
4.3. Hydrogen
Tables 7-A and 7-B and Figures 7 and 8 show experimental results of the effect of the ignition energy on the explosion indices of hydrogen. Table 8 compares the maximum explosion pressure, maximum rate of explosion pressure rise and the lower explosive limit of hydrogen for particular energies of ignition sources. Percentage changes related to the measurement with the lowest energy are also listed.
Figure 7.
Graph of explosion pressure depending on hydrogen concentration for various ignition energies.
Figure 8.
Graph of rate of explosion pressure rise depending on hydrogen concentration for various ignition energies.
Concentration (vol.%)
3.5
4
5
6
8
10
15
80 J
pm (bar)
0
0.1
0.4
0.9
1.7
2.8
4.3
(dp/dt)m(bar s−1)
0
5
9
8
10
22
232
160 J
pm (bar)
0
0.1
0.7
–
–
–
4.3
(dp/dt)m(bar s−1)
0
1
8
–
–
–
236
240 J
pm (bar)
0.1
0.1
0.7
–
–
–
4.3
(dp/dt)m(bar s−1)
2
3
9
–
–
–
261
Table 7-A.
Explosion indices of hydrogen.
Concentration (vol.%)
20
25
30
31
32
35
80 J
pm (bar)
5.4
6.4
6.9
7.1
7.0
6.8
(dp/dt)m(bar s−1)
838
1566
1899
2166
2091
2105
160 J
pm (bar)
–
6.4
7.0
7.0
7.0
6.8
(dp/dt)m(bar s−1)
–
1498
1880
2018
2203
2010
240 J
pm (bar)
–
6.3
6.8
7.0
7.0
7.0
(dp/dt)m(bar s−1)
–
1546
2170
2183
2288
2295
Table 7-B.
Explosion indices of hydrogen—part A.
80 J
160 J
Hydrogen percentage change (%)
240 J
Percentage change (%)
pm (bar)
7.1
7.0
−1.4
7.1
0.0
(dp/dt)m (bar s−1)
2324
2205
−5.1
2372
2.1
KGmax (bar s−1)
631
599
−5.1
644
2.1
LEL(vol.%)
3.5
4.0
14.3
3.5
0.0
Table 8.
Comparison of maximum explosion indices of hydrogen.
While methane was measured, the rate of explosion pressure rise increased by 32.2% using double energy (160 J) and it increased by 35.5% using triple energy (240 J). Maximum explosion pressure increased by 5.5% using double energy (160 J) and it increased by 4.1% using triple energy (240 J). The lower explosive limit did not change at double energy (160 J). LEL decreased by 22.2% using triple energy (240 J).
While propane was measured, the rate of explosion pressure rise increased by 20.0% using double energy (160 J) and it increased by 23.6% using triple energy (240 J). Maximum explosion pressure increased by 1.2% using double energy (160 J) and it had not changed using triple energy (240 J). The lower explosive limit did not change at double energy (160 J). LEL decreased by 25% using triple energy (240 J).
While hydrogen was measured, the rate of explosion pressure rise decreased by 5.1% using double energy (160 J) and it increased by 2.1% using triple energy (240 J). Maximum explosion pressure decreased by 1.2% using double energy (160 J) and it had not changed using triple energy (240 J). The lower explosive limit increased by 14.3% at double energy (160 J). LEL did not change using triple energy (240 J).
According to experimental data, the inference was made that the size of ignition energy affects especially the rate of explosion pressure rise and the lower explosive limit. Its effect on explosion pressure is only minimal.
This paper was financially supported by the project of grant ministry of interior the Czech Republic under the Id. No. VI20152019047, entitled “Development of the rescue destructive bombs for the disposal of statically damaged buildings".
References
1.Conrad, D., Kaulbars, R., 1995. Pressure dependence of the explosive limits of hydrogen, Chem.-Ing.-Tech. 67.
2.EN 1127-1 ED.2. 2011. Explosive atmospheres – Explosion prevention and protection – Part 1: Basic concepts and methodology. Brussel: CEN – European Committee for Standardization.
4.Material Safety Data Sheet—Hydrogen. In: [online]. [cit. 2016-04-22].http://prodkatalog.lindegas.cz/international/web/lg/cz/prodcatlgcz.nsf/RepositoryByAlias/BL8335/$file/BL8335.tif
5.Material Safety Data Sheet—Methane. In: [online]. [cit. 2016-04-22]. http://www.catp.cz/BL/BL8321.tif
6.Material Safety Data Sheet—Propane. In: [online]. [cit. 2016-04-22]. http://prodkatalog.linde-gas.cz/international/web/lg/cz/prodcatlgcz.nsf/RepositoryByAlias/BL0104/$file/BL0104.tif
7.Mynarz, M., Lepík, P., Serafín, J., 2012. Experimental determination of deflagration explosion characteristics of methane-air mixture and their verification by advanced numerical simulation, Twelfth International Conference on Structures under Shock and Impact, Kos, Greece, WIT Transactions on The Built Environment, Vol. 126, pp. 169–178. ISBN: 978-1-84564-612-7, ISSN: 1746-4498 (print).
8.Project SAFEKINEX: Report on experimental factors influencing explosion indices determination, 2002. Deliverable No. 2. Federal institute for materials research and testing (BAM). In: [online]. [cit. 2016-04-10].
Written By
Miroslav Mynarz, Petr Lepík and Jakub Melecha
Reviewed: 09 November 2016Published: 01 February 2017
Open access peer-reviewed conference paper
