Ionic Mechanisms of Soot Formation in Flames.
Abstract
The chemi-ion, ion-molecule mechanism of soot nucleation has been further examined by studies in premixed flames with Langmuir probes, molecular beam ion sampling mass spectrometry, and by flame temperature measurements. Langmuir probes were used to obtain absolute total ion concentrations in acetylene-oxygen flames over a range of equivalence ratios extending from stoichiometric mixtures to very sooty flames. These data were used in a preliminary calibration of the mass spectrometer. Two peaks in both total and individual positive ion concentration profiles were identified preceding the appearance of soot--the second peak occurred only at equivalence ratios very near the soot point or in sooty flames. The peak ion concentration decreased with increasing equivalence ratio well beyond the threshold equivalence ratio for soot formation. This refutes one of the arguments that has been used against the proposed mechanism, namely that ion concentrations increase at the equivalence ratio for soot formation. Means of treating particle electronics involved in sooty flames have been organized and applied to explain the effect of chemical additives on soot production. The effect of flame temperature (1700 to 2400 K) on soot threshold and soot yield was determined for a series of fuels. Increasing flame temperatures increased the soot threshold equivalence ratio with small temperature dependence, and decreased the soot volume fraction with a large temperature dependence. The results continue to support the chemi-ion, ion-molecule mechanism of soot nucleation. Originator furnished keywords include: Soot formation, Smoke, Ions in flames, Ion-molecule reactions, Flames, Combustion.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1984
- Accession Number
- ADA150119
Entities
People
- D. B. Olson
- H. F. Calcote