Open access peer-reviewed chapter

Effect of Size of Ignition Energy on the Explosion Behaviour of Selected Flammable Gas Mixtures

By Miroslav Mynarz, Petr Lepík and Jakub Melecha

Reviewed: November 9th 2016Published: February 1st 2017

DOI: 10.5772/66799

Downloaded: 563

Abstract

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.

Keywords

  • Explosion indices
  • 20-L apparatus
  • methane
  • Propane
  • Hydrogen
  • Ignition energy

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.%)
14.913.88.9
104.614.29.6
1004.315.110.8
10,0003.617.513.9

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).

2. Tested samples

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.

MethanePropaneHydrogen
Physical state at 20°C/101.3 kPaGasGasGas
Molar mass (g/mol)16.0444.002.01
Melting point (°C)−182−188−259
Boiling point (°C)−161−42−253
Density (kg/m3)0.6761.9100.090
Critical temperature (°C)−82.797.0−239.9
Critical pressure (MPa)4.604.250.13
Auto-ignition temperature (°C)595470560

Table 2.

Properties of tested gases (Material Safety Data Sheet-Methane, Propane, Hydrogen).

3. Experimental setup

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.

Figure 2.

Scheme of 20-L apparatus.

4. Measurement results

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

Concentration (vol.%)4.55678910111213
80 J
pm (bar)02.24.35.36.16.87.26.86.35.8
(dp/dt)m(bar s−1)01237821381651941458541
160 J
pm (bar)01.94.86.16.97.37.67.77.36.6
(dp/dt)m(bar s−1)0125815520922828021814676
240 J
pm (bar)0.10.13.04.76.16.77.27.67.36.9
(dp/dt)m(bar s−1)031768189216255290216133

Table 3. 

Properties of tested gases (Material Safety Data Sheet—Methane, Propane, Hydrogen).

80 J160 JMethane percentage change (%)240 JPercentage change (%)
pm(bar)7.37.75.57.64.1
(dp/dt)m (bar s−1)21428332.229035.5
KGmax(bar m s−1)587732.27935.5
LEL(vol.%)4.54.50.03.5−22.2

Table 4.

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.%)22.5344.5567
80 J
pm (bar)04.86.07.88.17.97.25.6
(dp/dt)m (bar s−1)04712226229023412536
160 J
pm (bar)05.26.27.78.38.37.56.6
(dp/dt)m (bar s−1)06318326936235017180
240 J
pm(bar)0.10.16.27.78.28.27.66.7
(dp/dt)m (bar s−1)0522342374329238121

Table 5.

 Explosion indices of propane.

80 J160 JPropane percentage change (%)240 JPercentage change (%)
pm (bar)8.28.31.28.20.0
(dp/dt)m(bar s−1)30536620.037723.6
KGmax (bar m s−1)839920.010223.6
LEL (vol.%)2.02.00.01.5−25.0

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.%)3.545681015
80 J
pm (bar)00.10.40.91.72.84.3
(dp/dt)m(bar s−1)05981022232
160 J
pm (bar)00.10.74.3
(dp/dt)m(bar s−1)018236
240 J
pm (bar)0.10.10.74.3
(dp/dt)m(bar s−1)239261

Table 7-A.

Explosion indices of hydrogen.

Concentration (vol.%)202530313235
80 J
pm (bar)5.46.46.97.17.06.8
(dp/dt)m(bar s−1)83815661899216620912105
160 J
pm (bar)6.47.07.07.06.8
(dp/dt)m(bar s−1)14981880201822032010
240 J
pm (bar)6.36.87.07.07.0
(dp/dt)m(bar s−1)15462170218322882295

Table 7-B.

Explosion indices of hydrogen—part A.

80 J160 JHydrogen percentage change (%)240 JPercentage change (%)
pm (bar)7.17.0−1.47.10.0
(dp/dt)m (bar s−1)23242205−5.123722.1
KGmax (bar s−1)631599−5.16442.1
LEL(vol.%)3.54.014.33.50.0

Table 8.

Comparison of maximum explosion indices of hydrogen.

5. Conclusion

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.

Acknowledgments

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".

© 2017 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Miroslav Mynarz, Petr Lepík and Jakub Melecha (February 1st 2017). Effect of Size of Ignition Energy on the Explosion Behaviour of Selected Flammable Gas Mixtures, Proceedings of the 2nd Czech-China Scientific Conference 2016, Jaromir Gottvald and Petr Praus, IntechOpen, DOI: 10.5772/66799. Available from:

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