Ignition of a hydrogen–air mixture by low voltage electrical contact arcs

Shekhar, Rajiv; Boeck, Lorenz R.; Uber, Carsten; Gerlach, U.

doi:10.1016/j.combustflame.2017.08.006

Cited by 13 publications

(20 citation statements)

References 7 publications

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“…This is problematic, firstly because the power loss due to this radiation is disregarded, and secondly, because the distribution is difficult to accurately measure by experiment. Although previous research [4] found that qualitative features of the flammable gas ignition were adequately predicted by this empirical approach, a more physically realistic approach would be more satisfactory, and could potentially approach quantitative accuracy without arbitrary model tuning. Conventional simulation methods which use a temperatureelectrical conductivity curve to couple hydrodynamics to electromagnetic equations cannot be used to solve this problem, as they rely on the LTE assumption.…”

Section: Resultsmentioning

confidence: 97%

“…A similar approach to Ref. [4,8] is taken, applying it to the recent dataset of Ref. [10] and adding a more detailed consideration of varying arc geometry.…”

Section: Empirical Discharge Modelmentioning

confidence: 99%

“…A similar approach to Ref. [4,8] is taken, applying it to the recent dataset of Ref. [10] An example of this data for one discharge event is shown in figure 2.…”

Section: Empirical Discharge Modelmentioning

confidence: 99%

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Numerical investigation of transient, low-power metal vapour discharges occurring in near limit ignitions of flammable gas

Shekhar¹,

Gortschakow²,

Großhans³

et al. 2018

J. Phys. D: Appl. Phys.

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This article presents an investigation of a transient (30 µs -5 ms) electrical discharge in metal vapour with low voltage (≤ 30 V) and current (≤ 200 mA), drawn between two separating electrodes. Discharges of this type are rarely studied, but are important in electrical explosion safety, as they can ignite flammable gasses. An empirical model is developed based on transient recordings of discharge voltages and currents and high speed broadband image data. The model is used for predicting the electrical waveforms and spatial power distribution of the discharge. The predicted electrical waveforms show good accuracy under various scenarios. To further investigate the underlying physics, the model is then incorporated into a simplified 3-D gas dynamics simulation including molecular diffusion, heat transfer and evaporation of metal from the electrode surface. The local thermodynamic equilibrium (LTE) assumption is next used to calculate electrical conductivity from the simulated temperature fields, which in turn is integrated to produce electrical resistance over time. This resistance is then compared to that implied by the voltage and current waveforms predicted by the empirical model. The comparison shows a significant discrepancy, yielding the important insight that the studied discharge very likely deviates strongly from LTE.

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Section: Resultsmentioning

confidence: 97%

“…A similar approach to Ref. [4,8] is taken, applying it to the recent dataset of Ref. [10] and adding a more detailed consideration of varying arc geometry.…”

Section: Empirical Discharge Modelmentioning

confidence: 99%

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Numerical investigation of transient, low-power metal vapour discharges occurring in near limit ignitions of flammable gas

Shekhar¹,

Gortschakow²,

Großhans³

et al. 2018

J. Phys. D: Appl. Phys.

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“…e IISBBCs were tested by the IEC spark test apparatus. e IEC spark test apparatus [28] and its structure are shown in Figure 16, where the tungsten wire and the cadmium disk are the disconnected electrodes.…”

Section: Explosive Test Based On the Iec Spark Test Apparatusmentioning

confidence: 99%

Optimal Design Method for Inner-Intrinsically Safe Buck-Boost Converters Based on Ignition Capability

Yongxiu

2021

Mathematical Problems in Engineering

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Intrinsically safe switching converters are the best choice for low-voltage DC power supplies in explosive environments (such as coal mine). To obtain the optimal design method of the inner-intrinsically safe buck-boost converter (IISBBC), the equivalent circuits for various switching states and operating conditions of the buck-boost converter are studied, and the most dangerous inductor-disconnected discharge (IDD) condition of the buck-boost converter is obtained. Based on this condition, the IDD behavior of the IISBBC is studied. According to the minimum ignition curves (MICs) of the resistive circuit and the simple inductive circuit, the expressions describing the IDD ignition capability of the IISBBC in terms of the critical ignition power and the critical ignition energy are derived. The IDD has the strongest ignition capability based on power when the IISBBC is working at its maximum input voltage and minimum load resistance, and it has the strongest ignition capability based on energy when the IISBBC is working at its minimum input voltage and minimum load resistance. The converter is inner-intrinsically safe only when the maximum arc power is less than the critical ignition power and the inductive energy is less than its critical value. By incorporating the proposed criterion, the optimal design method for IISBBCs that meets the demands of electric and inner-intrinsic safety performance is obtained. Based on this method, the design range of the inductance and capacitance and the optimal inductance to give the IISBBC the best inner-intrinsic safety performance are obtained. The feasibility and reliability of the proposed optimal design method are demonstrated by an explosion test.

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“…Inspection of figure 3.7 suggests a value of around 400 µm for this minimum radius, however a more detailed investigation has found that it depends on the transient properties of the discharge, where the minimum radius increases for a longer discharge [64]. It has been theorised that, because the flame front propagates further away from the discharge for a longer discharge duration, the efficiency of energy input into the flame is reduced [44].…”

Section: Simulationmentioning

confidence: 98%

Modelling of ignition by low voltage electrical discharges in explosion protection applications

Shekhar¹

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who provided extensive guidance and at many times went out on a limb to support the work. Special thanks are also due to my fellow doctoral candidate Carsten Uber for the very rewarding scientific collaboration. Additionally, to Thomas Uehlken for lending his outstanding engineering expertise to the project and without whom I could not have settled into a new job in a new country so easily. I am also grateful to Dr. Holger Grosshans, whose expert knowledge of fluid dynamics was vital in bringing the project to a close.Undertaking such a multi-faceted project requiring specialist knowledge across many different disciplines would not have been possible without the right collaboration partners. In this regard, I owe a debt of gratitude to Dr. Lorenz R. Boeck and Prof. Joseph E. Shepherd, whose collaborative work at the Caltech Explosion Dynamics Laboratory brought the idea of a quantitative experimental study using optical combustion diagnostics to fruition. Similarly, the plasma physics related contributions of Dr. Sergey Gortschakow and Prof. Dirk Uhrlandt of the Leibniz Institute for Plasma Research are gratefully acknowledged. I would also like to thank my supervisors at the University of Queensland, Dr. Rahul Sharma and Prof. Tapan Saha for their assistance in meeting university requirements and their patience with what was a rather unconventional subject matter and working arrangement. Thanks are also due Prof. Paul Lever and Mining3, who inspired me to take up this project and provided continuing support for the work.Last, but not least, I am grateful to my family and friends for their love and support.To my parents, for their constant encouragement throughout the extended absence from my home country, and to Swami Baneshananda and the Vedanta Gesellschaft, who never let me forget that the true calling of man is so much greater than mere work and enjoyment.

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Ignition of a hydrogen–air mixture by low voltage electrical contact arcs

Cited by 13 publications

References 7 publications

Numerical investigation of transient, low-power metal vapour discharges occurring in near limit ignitions of flammable gas

Numerical investigation of transient, low-power metal vapour discharges occurring in near limit ignitions of flammable gas

Optimal Design Method for Inner-Intrinsically Safe Buck-Boost Converters Based on Ignition Capability

Modelling of ignition by low voltage electrical discharges in explosion protection applications

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