DETAILED KINETIC MODELING OF SOOT FORMATION DURING SHOCK-TUBE PYROLYSIS OF C₆H₆: DIRECT COMPARISON WITH THE RESULTS OF TIME-RESOLVED LASER-INDUCED INCANDESCENCE (LII) AND CW-LASER EXTINCTION MEASUREMENTS

Abstract

The results of calculations of the main parameters of the soot formation process (t, k f , SY, and r m ) carried out with the use of the detailed kinetic model of soot formation are compared with the experimental measurements of these parameters by the continuous-wave (CW)-laser extinction technique and by the time-resolved laser-induced incandescence (LII) method during C 6 H 6 pyrolysis behind reflected shock waves. The detailed kinetic model of soot formation that is developed incorporates the gas-phase mechanisms of acetylene pyrolysis and the mechanisms of formation of polyaromatic hydrocarbons, polyyne molecules, and pure carbon clusters. It combines the H abstraction=C 2 H 2 addition and polyyne pathways of the soot formation process. The formation, growth, and coagulation of soot precursors and soot particles are described within the framework of the discrete Galerkin technique based on an error-controlled expansion of the size distribution function of heterogeneous species into the orthogonal polynomials of a discrete variable (in particular, the number of monomers in the heterogeneous particle) that makes it possible to preserve a discrete character of any elementary transformations of heterogeneous particles and to describe them as elementary chemical reactions for the heterogeneous particles of all sizes. The comparison of the calculations with the experimental measurements of the induction time t, observable rate of soot particle growth, k f , and soot yield SY by the CW-laser extinction method in the pyrolysis of benzene=argon mixtures in shock-tube experiments clearly demonstrates that the coincidence is quantitatively good for all the main parameters of soot formation. A particular difference between the values of the mean soot particle radius r m experimentally measured by the time-resolved LII technique and calculated with the help of the detailed kinetic model is observed at the low and high temperatures. The results presented demonstrate the current level of the predictive capabilities of the detailed kinetic model of soot formation and the reliability of the time-resolved LII technique for the quantitative determination of the soot particle sizes.

Catalytic Dry Reforming of Methane: Insights from Model Systems

“…The formation of light hydrocarbons by radical recombination reactions, with resulting products such as acetylene (C 2 H 2 ) and small olefins may be source to the formation of even heavier coke precursor species. Combination reactions of acetylene, and alternatively addition and dehydrogenation steps of small olefins like ethylene and propylene, may give rise to increasing concentration of aromatics (C 6 H 6 ) and polycyclic aromatic hydrocarbons (PAHs) which are also highly potent coke precursors. The consequences of these findings are fundamental in nature: not only is C1 related coke build‐up highly relevant, but even if present in much lower concentration in the feed, coke precursors like acetylene, small olefins and aromatics are present and any catalyst material will be subject to the consequences of their presence.…”

Modelling of Particulate Processes

“…They incorporated the mean value of fractal dimension into their model as well as the agglomerate collision diameter and the number of primary particles. Not using PARSIVAL or PREDICI but based on Wulkow's earlier work, Vlasov, Warnatz and co-workers employed a finite element code to simulate the formation of soot in a shock tube 119,80) .…”

Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics

“…The majority of studies on soot formation concern shock-tube pyrolysis and laminar flame techniques. 5,6 There is considerable evidence that PAHs play a key role in soot formation, although other reaction pathways involving polyacetylenes and ionic species have been suggested. 82 There are several comprehensive reviews on the chemical pathways of soot formation; 4, 80, 81 generally four phases (P) in soot formation can be distinguished P1: The phase in which small molecular precursors to soot (such as small aromatic species like benzene or naphthalene) are either present or formed.…”

“…The combination of the mutagenic and/or carcinogenic properties of many PAHs 1,2 and their efficient formation during the incomplete combustion of organic materials, has resulted in a large effort to understand the fundamental role of PAHs in combustion chemistry. 3,4 Hence, their physical and chemical properties have been extensively studied under a variety of environmentally relevant experimental conditions, e.g., in shock-tube pyrolysis 5,6 and flame combustion studies. 7,8 Due to their strong affinities to carbonaceous matter, such as coal or soot, the occurrence of PAHs in fine particulate matter in the atmosphere and their formation, e.g., in the context of black carbon particles, 9 is of significant interest in atmospheric/environmental sciences.…”