The origin of soot in flames: Is the nucleus an ion?

被引:42
作者
Hall-Roberts, VJ [1 ]
Hayhurst, AN [1 ]
Knight, DE [1 ]
Taylor, SG [1 ]
机构
[1] Univ Cambridge, Dept Chem Engn, Cambridge CB2 3RA, England
关键词
D O I
10.1016/S0010-2180(99)00116-9
中图分类号
O414.1 [热力学];
学科分类号
摘要
There are two schools of thought on how soot originates in a fuel-rich flame. On the one hand, the ionic theory postulates that small ions, such as C3H3+, act as nuclei, so that species such as C2H2 and C4H2 add onto them, and occasionally liberate H-2 in a repetitive growth process. Once these ions become large (approximate to 2000 a.m.u.) they supposedly dissociate and produce an uncharged, but large, hydrocarbon "molecule," which can grow, coalesce or coagulate to give soot particles. Simultaneously this dissociation produces avery small ion, which repeats the process of adding on C-2, C-3. and C-4 species, etc. The other school of thought believes that fairly similar processes occur, but the species involved are not ions, but uncharged radicals and molecules. This present study has spectroscopically monitored the level of sooting in the earliest stages of its production in a premixed, oxyacetylene flame at 1 atm. If soot originates from ions such as C3H3+, the addition of a relatively large quantity of easily ionized cesium removes C3H3+ ions from the flame. In that case there should also be less soot produced. When either distilled water or a strong aqueous solution of CsCl was nebulized into the sooting flame, the intensity of the emission fell. by the same amount. This was by only similar to 1% in the earliest part of the burned gas, but rose to a larger drop farther downstream of the reaction zone. Thus cesium itself has no effect on the sooting level early in this premixed flame, indicating that there is no evidence here for ions acting as nuclei for soot. However, the addition of water alone does inhibit the production of seat. (C) 2000 by The Combustion Institute.
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页码:578 / 584
页数:7
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