The spark discharge characteristics and the minimum ignition energy of capacitor discharge ignition (CDI) systems, were investigated using several types of ignition coils and primary capacitors. The mechanism of energy transfer from the primary capacitor to the spark is explained by a simple theory taking into account the spark voltage-current characteristics. The minimum ignition energy for propane-air mixtures is lowest for sparks of about 100 kHz frequency and 20-50 #x3BC;sec duration. In order to evaluate the igniting ability of a total system, the minimum stored energy needed for ignition is employed. The lowest values of these two minimum energies can be obtained by ignition coils whose specifications are considerably different from those of currently used coils.
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