Ionization of in-cylinder charge during preflame period in compression ignition of mixtures

Ion formation has been detected in cool and blue flames that appear during the preflame period of mixture ignition caused in a rapid compression machine. An ionization gap was installed in the combustion chamber. Ion current level is much lower than that of normally observed in propagation flames, but highly reproducible. Ions arise at the time the cool flame degenerates, and again in the blue-flame induction time T2. Breakdown of electric non-conductance during the preflame period has been investigated recently using a motored premixed-compression ignition engine. An electrode gap was installed in the combustion chamber. Between the electrodes a high static voltage of 2 200 V was given, charged in a small capacitor. It has been found that the timing of discharge or break down during the preflame period was the time in which the cool flame began to appear. Several attempts have been made to detect ionization of low-temperature flames produced by piston compression or on a flat burner, and to obtain advanced knowledge on the role the low-temperature reactions, which perform for the onset of final hot-flame ignition.