The roles of PAH (polycyclic aromatic hydrocarbons) and acetylene in soot nucleation and growth

Conference · Sun Dec 31 23:00:00 EST 1989

OSTI ID:7170203

McKinnon, J T; Howard, J B

Soot nucleation and growth mechanisms involving PAH and C{sub 2}H{sub 2} in distinct roles were quantitatively tested against experimental data including profiles of soot, PAH, C{sub 2}H{sub 2} and other species present in flat benzene/oxygen/argon flames at 20 and 40 torr and equivalence ratios of 2.0, 2.125, and 2.4. In all the flames, the concentration of high molecular weight PAH was found to exhibit a maximum value near the onset of soot nucleation and to decline in the nucleation zone. A nucleation mechanism involving growth by reactive coagulation of heavy PAH in competition with destruction through OH attack gave good agreement between measured and predicted features of the soot nucleation kinetics. Conversely, soot nucleation through the growth of PAH by sequential addition of C{sub 2}H{sub 2} with no PAH-PAH coagulation was much too slow to agree with data. PAH also contribute significantly to the post-nucleation growth of soot particles. Most of the mass of the soot system appears to come from C{sub 2}H{sub 2} through the formation of the heavy PAH precursors to soot nuclei and the PAH that add to the growing soot particles, and direct C{sub 2}H{sub 2} addition to the soot. Both the growth and oxidation reactions in these mechanisms are formulated as involving localized {sigma}-radicals (i.e. aryl radicals in the case of PAH and active sites in the case of soot). The fraction of aryl radicals in the PAH and of active sites among carbon atoms of the soot surface are assumed to depend on a partial equilibrium involving the gas-phase concentration of H and H{sub 2}. The decrease in the surface growth rate of soot with time can be attributed in part to the decay in gas-phase concentration and a reduction in the hydrogen content of the soot. 29 refs., 5 figs., 3 tabs.

• Research Organization: Massachusetts Inst. of Tech., Cambridge, MA (USA). Dept. of Chemical Engineering
• Sponsoring Organization: DOE/ER
• DOE Contract Number: FG02-84ER13282
• OSTI ID: 7170203
• Report Number(s): CONF-900704-9; ON: DE90009022
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
ACETYLENE
ALKYNES
AROMATICS
ARYL RADICALS
CHEMICAL REACTIONS
FLAMES
HYDROCARBONS
NUCLEATION
ORGANIC COMPOUNDS
PARTICLE SIZE
PHENYL RADICALS
POLYCYCLIC AROMATIC HYDROCARBONS
RADICALS
SIZE
SOOT
SURFACES