Soot Formation In Pyrolysis Research Articles

Influence of methane addition on soot formation in pyrolysis of acetylene

Time-resolved laser-induced incandescence for particle sizing and laser light extinction for soot volume fraction was applied simultaneously to study the influence of methane addition on soot formation in acetylene pyrolysis. Three series of the experiments with initial mixtures of 2% C2H2 + Ar, 1% CH4 + Ar and 2% C2H2 + 0.5/1/2% CH4 + Ar in the temperature range of 1600–2300 K and the pressure range of 4–5 bar behind reflected shock waves were carried out. The kinetic characteristic of the soot formation process—the induction time of soot particle inception as well as the temperature dependences of final values of soot volume fraction and particle sizes have been determined and analyzed. An essential increase of soot volume fraction, particle sizes and a decrease of induction time of soot inception at methane addition to acetylene were observed. The gas phase kinetic modeling of the investigated processes up to the soot nuclei precursors formation has been performed. Analysis of gas kinetic stages of acetylene decomposition with methane addition has demonstrated the significant increase of the rates of pyrene formation followed by PAH growth due to effective propargyl C3H3 formation.

ICOPE-15-1125 Effects of hydrogen addition on soot formation in pyrolysis of iso-octane behind a reflected shock wave

This paper discusses the effects of hydrogen addition on soot formation in iso-octane pyrolysis using a shock tube. In the experiments, 1% iso-C_8H_<18> + 99% Ar and 1% iso-C_8H_<18> + 1% H_2 + 98% Ar are used as a test gas in the temperature range of 1800-2600 K and in the pressure of 1.2 ± 0.1 MPa behind a reflected shock wave. Soot formation process was characterized by induction time and soot volume fraction, which is obtained from laser light extinction measurement. In addition, time history of soot particles temperature was calculated based on spectral dependence of monochromatic emissive power from thermal radiation from the soot particles. The experimental results show that soot formation had bell-shaped temperature dependence exhibiting maximum at 2000 K with and without hydrogen addition. Adding hydrogen to iso-octane, soot volume fraction reduced for T_5 = 1800 K. Additionally, induction time increased for T_5 = 1800 K and 2000 K. Soot particle temperature T_P was higher than T_5 by about 200-400 K except for around 1800 K. Consequently, hydrogen addition to iso-octane suppressed soot formation for T_5 = 1800 K, while no distinct effects of hydrogen addition were observed for T_5 = 2000 K and 2500 K.

Detailed kinetic modeling of soot formation in shock tube pyrolysis and oxidation of toluene and n-heptane

A new detailed kinetic model of soot formation in shock tube pyrolysis and oxidation of aliphatic and aromatic hydrocarbons is proposed. The model is based on the comprehensive kinetic model of PAH formation and growth [H. Richter, J.B. Howard, Phys. Chem. Chem. Phys. 4 (2002) 2038–2055; H. Richter, S. Granata, W.H. Green, J.B. Howard, Proc. Combust. Inst. 30 (2005) 1397–1405; J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122–136; M. Frenklach, D.W. Clary, T. Yuan, W.C. Gardiner, Jr., S.E. Stein, Combust. Sci. Tech. 50 (1986) 79–115; M. Frenklach, J. Warnatz, Combust. Sci. Tech. 51 (1987) 265–283; M.S. Skjøth-Rasmussen, P. Glarborg, M. Østberg, J.T. Johannessen, H. Livbjerg, A.D. Jensen, T.S. Christensen, Combust. Flame 136 (2004) 91–128], on the new concepts of soot particle nucleation [A. Violi, Combust. Flame 139 (2004) 279–287; A. Violi, A.F. Sarofim, G.A. Voth, Combust. Sci. Tech. 176 (2004) 991–1005; A. D’Alessio, A. D’Anna, P. Minutolo, L.A. Sgro, A. Violi, Proc. Combust. Inst. 28 (2000) 2547–2554; A. D’Anna, A. Violi, A.D’Alessio, A.F. Sarofim, Combust. Flame 127 (2001) 1995–2003] and the traditional H-abstraction/C 2H 2-addition (HACA) route of PAH and soot particles surface growth [H. Wang, M. Frenklach, Combust. Flame 110 (1997) 173–221; J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122–136]. The gas-phase kinetic scheme was validated against the experimentally measured concentration profiles of the main gas-phase species formed during toluene pyrolysis and H and OH radicals during benzene and phenol pyrolysis and toluene oxidation behind reflected shock waves. The model describes the main characteristics of soot formation in pyrolysis and oxidation of toluene and n-heptane oxidation under conditions typical of shock tube experiments. Both hydrocarbons have the same number of carbon atoms but different structures, which causes different behavior of the systems. The discrete Galerkin technique was applied for direct counting of the mean number of active sites formed on the surface of soot precursors and soot particles in reactions of activation, deactivation, and surface growth.

Detailed modeling of soot formation in hydrocarbon pyrolysis

Extended calculations of soot formation in the pyrolysis of a number of hydrocarbons varying in chemical structure have been performed. The computer code for soot formation was based on the “polyyne model”, which uses the “acetylene pathway” to soot particles. The model treats soot formation as a process of chemical condensation (polymerization) of supersaturated polyyne vapor (C 2 n H 2, n = 2, 3, … ). This process results in polymeric globules as primary soot particles. The computer code is based on a detailed description of both gas-phase and heterogeneous reactions, soot particle nucleation, their surface growth and coalescence. The principal parameters for soot formation, such as induction time, soot particle number density, and soot volume fraction over a wide temperature range have been calculated. There is good quantitative agreement between these calculations and available experimental measurements for methane, acetylene, ethylene, diacetylene, benzene, and naphthalene as fuel.

Shock-tube pyrolysis of chlorinated hydrocarbons: Formation of soot

Soot formation in pyrolysis of chlorinated methanes, their mixtures with methane, and chlorinated ethylenes were studied behind reflected shock waves by monitoring the attenuation of an HeNe laser beam. An additional single-pulse shock-tube study was conducted for the pyrolysis of methane, methyl chloride, and dichloromethane. The experiments were performed at temperatures 1300–3000K, pressures 0.4–3.6 bar, and total carbon atom concentrations (1–5) × 10 17 atoms/cm 3. The amounts of soot produced in the pyrolysis of chlorinated hydrocarbons are larger than that of their nonchlorinated counterparts. The sooting behavior and product distribution can be generally explained in terms of chlorine-catalyzed chemical reaction mechanisms. The pathway to soot from chlorinated methanes and ethylenes with high H : Cl ratio proceeds via the formation of C 2H, C 2H 2, and C 2H 3 species. For chlorinated hydrocarbons with low H : Cl ratio, the formation of C 2 and its contribution to soot formation at high temperatures becomes significant. There is evidence for the importance of CHCl radical and its reactions in the pyrolysis of dichloromethane.

A conceptual model for soot formation in pyrolysis of aromatic hydrocarbons

Soot formation in toluene-argon mixtures has been investigated behind reflected shock waves by monitoring attenuation of a laser beam in both the visible (632.8nm) and the infrared (3.39 μm) regions of the spectrum. The experiments were carried out at nearly constant total carbon atom concentration over temperature and pressure ranges of approximately 1500–2300K and 0.03–0.3 MPa, respectively. The experimental data indicate that there is a strong pressure effect on soot formation at lower pressures. The bell-shaped dependence of soot conversion on temperature shifts toward higher temperatures with decreasing pressure. The observed phenomenon can not be rationalized within Graham's model. A new conceptual model for soot formation is proposed that not only explains the current results but also unifies the various experimental facts which previously had been considered to be contradictory. The ratio of induction times for soot appearance in the visible and infrared regions was observed to be approximately constant over a wide temperature range, which is also in harmony with the proposed model.