Measurement of minimum electric spark ignition energy of dust clouds in the energy range 0.1-10 mJ

Basic context: An electric spark is a complex ignition source, and a dust cloud is a complex fuel. The very hot plasma generated, by dissipating electric energy in the gap between the spark electrodes, transfers heat to the dust particles both by thermal radiation and convection/conduction. The high concentration of reactive chemical radicals in the plasma probably enhances the ignition process. On the other hand rapid expansion of the spark channel to ambient pressure can hamper the ignition process by pushing dust particles away from the spark zone. The proposed measurements of MIE as a function of spark discharge duration can help in resolving the complex ignition mechanism. Practical context: IEC (International Electrotechnical Commission) and CENE LEC (corresponding European Union org.) issued their new standards for determination of MIEs of dust clouds a few years ago. CEN (another European Union org.) is currently producing a similar standard. In all three standards the lower energy limit of the test methods is about 3-5 mJ, due to basic limitations in the spark generation concepts used. Hence, with the present generators it is impossible to resolve differences between MIE values below this limit, in spite of the fact that quite a few very sensi tive dusts most probably have MIEs well below 1 mJ. The prosed project will provide the experim ental method needed to obtain the required resolution in this range.