Ionic Mechanisms of Soot Formation in Flames.

Experimental measurements have been made and interpreted in acetyleneoxygen and benzeneoxygenargon flames at 2.7 kPa, and an unburned flow velocity of 50 cms with the objective of evaluating the ionic mechanism of soot nucleation. This mechanism postulates that chemi-ions are precursors of soot and that the initial reactions in the soot and nucleation process are ion-molecule reactions in which molecular ions continually increase in size until they are neutralized by ion combination. Total ion profiles were determined by Langmuir probe individual ion profiles were determined by Langmuir probe individual ion profiles were determined by molecular ion sampling mass spectrometry up to about mass 600 temperature profiles were determined by radiation corrected thermocouples. It is demonstrated that the ion concentration is greater that the concentration of soot particles and ions decay as soot is produced. In the acetyleneoxygen, the ion-molecule reaction rates are measured and compared with other measured and calculated rates. It is demonstrated that these rates are rapid at flame temperatures. Some major differences were found in the features of benzene and acetylene ion profiles that remain to be explained. The experiments are strongly supportive of the ion mechanism of soot formation in flames.