Capacitive sparks

Brush Discharge With dusts with MIE values of less than 3 mJ determined with purely capacitive spark discharges (without induc-... 

Kono, M., Kumagai, S., and Sakai, T., Ignition of gases by two successive sparks with reference to frequency effect of capacitance sparks. Combust. Flame, 27, 85 1976. 

Capacitive discharges are characterized by the electrostatic energy Ue converted to thermal energy in the spark. While somewhat difficult to measure accurately, the energy released in a capacitive spark is commonly estimated using the following relationship. 

Two other useful parameters related to capacitive sparks and dust ignitions are (i) the optimum sparking distance is 10 mm and (ii) the quenching distance is 7 mm. Refer to Sec. 4.1 and Table 5, where MIE is discussed in more detail. 

Equation 7-20 assumes a capacitance-type discharge (that is, a spark) however, capacitance and voltage are not defined in nonconductive systems. Therefore Equation 7-20 is valid only for capacitive sparks, but it is used qualitatively for the other discharges. 

Minimum ignition energy test is performed in accordance with ASTM E2019, British Standard 5958, and International Standard lEC 1241-2-3 using the modified Hartmann tube apparatus. Dust samples of various sizes are dispersed in a 1.2 L vertical tube and attempts are made to ignite the resultant dust cloud with discrete capacitive sparks of known energy. 

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