Correlating minimum ignition criteria

1994 ◽  
Vol 447 (1931) ◽  
pp. 513-526 ◽  
Keyword(s):  
Electrical Energy ◽  
Laser Wavelength ◽  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Power Flux ◽  
Small Areas ◽  
Quenching Distance ◽  
Safety Considerations ◽  
Short Time ◽  
Target Combination

Potential hazards associated with the use of optical fibres carrying laser beams in flammable atmospheres have prompted a series of ignition studies. Investigations are described in which diverse target materials are exposed to radiation from various lasers in a variety of flammable mixtures. A distinctive feature of these systems is that ignition by a laser beam expanding from a fine optical fibre, interacting with particles of varying size and position, can, with minor adjustments to the geometry, give rise to wide variations in irradiated area and duration. This contrasts with the more customary circumstances in which the criterion is either a minimum ignition energy (short time, small dimensions) or an ignition temperature (long times, large dimensions). It is shown that the laser ignition criteria of a minimum power flux at large areas and minimum igniting power for small areas may be interpreted in terms of an igniting energy increasing linearly with time and area, but tending to constant values for dimensions smaller than the quenching distance. A general theory is developed, correlating the various ignition criteria with each other and with fundamental combustion parameters. The hazard may be related to corresponding safety considerations for the dissipation of electrical energy in flammable atmospheres by taking into account the absorptivity/emissivity characteristics of each particular laser wavelength/target combination.

Ignition and flame quenching of quiescent fuel mists

1978 ◽  
Vol 364 (1717) ◽  
pp. 277-294 ◽  
Keyword(s):  
Reaction Rates ◽  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Proposed Model ◽  
Theoretical Predictions ◽  
Quenching Distance ◽  
Experimental Values ◽  
Sole Criterion ◽  
Fuel Vapour ◽  
Level Of Agreement

A model is proposed for the ignition of quiescent multidroplet fuel mists which assumes that chemical reaction rates are infinitely fast, and that the sole criterion for successful ignition is the generation, by the spark, of an adequate concentration of fuel vapour in the ignition zone. From analysis of the relevant heat transfer and evaporation processes involved, ex­pressions are derived for the prediction of quenching distance and minimum ignition energy. Support for the model is demonstrated by a close level of agreement between theoretical predictions of minimum ignition energy and the corresponding experimental values obtained using a specially designed ignition apparatus in which ignition energies are measured for several different fuels, over wide ranges of pressure, mixture composition and mean drop size. The results show that both quenching distance and mini­mum ignition energy are strongly dependent on droplet size, and are also dependent, but to a lesser extent, on air density, equivalence ratio and fuel volatility. An expression is derived to indicate the range of drop sizes over which the proposed model is valid.

Minimum ignition energy and quenching distance of aluminum dust clouds

2021 ◽  
Author(s):  
Meet Parikh ◽  
Rinrin Saeki ◽  
Rajib Mondal ◽  
Kwangseok Choi ◽  
Wookyung Kim
Keyword(s):  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Dust Clouds ◽  
Quenching Distance

Ignition and flame quenching in flowing gaseous mixtures

1977 ◽  
Vol 357 (1689) ◽  
pp. 163-181 ◽  
Keyword(s):  
Combustible Mixture ◽  
Inert Gases ◽  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Turbulence Scale ◽  
Gaseous Mixtures ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Quenching Distance ◽  
Velocity Turbulence

The influence of pressure, velocity, turbulence intensity, turbulence scale and mixture composition on minimum ignition energy and quenching distance in flowing gaseous mixtures is examined experimentally for methane and propane fuels. In some experiments, the nitrogen in the air is replaced by various inert gases such as carbon dioxide, helium or argon, while in others the nitrogen is either partly or totally replaced by oxygen. The tests are conducted at room temperature in a 9 cm square working section through which the combustible mixture is arranged to flow at various levels of pressure, turbulence and velocity. At each test condition, the spark energy required to ignite the flowing mixture is measured for several gap widths in order to establish the optimum gap width corresponding to minimum ignition energy. From analysis of the relevant combustion and heat transfer processes involved, expressions for the prediction of quenching distance in flowing mixtures are derived. Support for the model employed in this analysis is demonstrated by a close level of agreement between theoretical predictions of quenching distance and corresponding values calculated from the experimental data on minimum ignition energy obtained over a wide range of mixture compositions and flow conditions.

The ignition of primary explosives by electric discharges

1958 ◽  
Vol 246 (1245) ◽  
pp. 189-196 ◽  
Keyword(s):  
Electrical Energy ◽  
Systematic Investigation ◽  
Test Methods ◽  
Extensive Literature ◽  
Electric Discharges ◽  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Number Of Factors ◽  
Experimental Values ◽  
Energy Dissipated

It has long been known that explosives can be ignited by electric sparks. Compounds such as lead styphnate are particularly sensitive, and electric discharges, arely visible to the naked eye, are capable of igniting them. This is a source of azard in the manufacture and handling of those primary explosives used as itiatory materials, and there is an extensive literature on methods of measurement and on experimental values of the minimum ignition energy of these materials Langevin & Bicquard 1934; Brown, Kusler & Gibson 1946; Morris 1947, 1953; Lathsburg & Schmitz 1949). A review of the literature followed by some experimental determinations, showed that widely varying values of ignition energy ould be obtained for the same substance by using different experimental test methods and conditions. A systematic investigation of this problem by Wyatt, Moore and Sumner at the Explosive Research and Development Establishment, Waltham Abbey, has revealed a number of factors which influence the ignition energy and this paper presents a brief summary of some aspects of their work. There are two types of test apparatus commonly used to measure the ease of ignition of initiator materials by electric sparks; first, a fixed-gap method in which e voltage is applied across two electrodes, one of which is covered by the material sted, the voltage being sufficient to break down the gap and cause a spark to ass; second, an approaching-electrode method in which the gap is initially too ide for a discharge to take place with the voltage applied, but a spark is produced moving one electrode towards the other. The energy dissipated in the discharge varied by changing the applied voltage or the capacity of the condenser used to ore the electrical energy.

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