Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways

Chemical kinetic modeling of hydrocarbon combustion

Gas-phase tropospheric chemistry of organic compounds: A review

Detailed modeling of soot particle nucleation and growth in laminar premixed hydrocarbon flames is presented. The model begins with fuel pyrolysis, followed by the formation of polycyclic aromatic hydrocarbons, their planar growth and coagulation into spherical particles, and finally, surface growth and oxidation of the particles. The computational results are in quantitative agreement with experimental results from several laminar premixed hydrocarbon flames. A detailed analysis of soot particle inception and surface growth processes is presented. Surface growth was described in terms of elementary chemical reactions of surface active sites. The density of these sites was found to depend on the chemical environment. The model predicts the classical picture of soot particle inception and the classical description of soot particle structure.

Detailed modeling of soot particle nucleation and growth

A detailed chemical kinetic mechanism has been developed to describe the oxidation of small hydrocarbon and oxygenated hydrocarbon species. The reactivity of these small fuels and intermediates is of critical importance in understanding and accurately describing the combustion characteristics, such as ignition delay time, flame speed, and emissions of practical fuels. The chosen rate expressions have been assembled through critical evaluation of the literature, with minimum optimization performed. The mechanism has been validated over a wide range of initial conditions and experimental devices, including flow reactor, shock tube, jet-stirred reactor, and flame studies. The current mechanism contains accurate kinetic descriptions for saturated and unsaturated hydrocarbons, namely methane, ethane, ethylene, and acetylene, and oxygenated species; formaldehyde, methanol, acetaldehyde, and ethanol.

A Hierarchical and Comparative Kinetic Modeling Study of C1 − C2 Hydrocarbon and Oxygenated Fuels

The Surface Growth Phenomenon in Soot Formation

The chemical equilibrium Br + CH3OH ⇌ HBr + CH2OH (1, −1) has been studied by investigating the kinetics of the forward and reverse reactions. Excimer laser photolysis coupled with Br atom resonance fluorescence detection was used over the temperature range 439−713 K to obtain k1 = (3.41 ± 0.89) × 109T1.5 exp[−(29.93 ± 1.47) kJ mol-1/RT] cm3 mol-1 s-1. The reverse reaction was studied with the fast flow technique, in the temperature range 220−473 K, using laser magnetic resonance for monitoring the CH2OH radicals. Thus, k-1 = (1.20 ± 0.25) × 1012 exp[(3.24 ± 0.44) kJ mol-1/RT] was obtained. The kinetic results were compared with available literature data and possible causes of the deviations were discussed. Kinetic information on the foward and back reactions was combined to obtain the heat of formation for CH2OH. Both second-law and third-law procedures were used in the derivations, giving a recommended value of ΔfH°298(CH2OH) = −16.6 ± 1.3 kJ mol-1, which corresponds to the C−H bond dissociation energy ...

Direct Kinetic Studies of the Reactions Br + CH3OH and CH2OH + HBr: The Heat of Formation of CH2OH

The reaction between CH2-radicals in their ground electronic state (X3B1) and n-hexane










was studied in a discharge flow system with LMR detection of CH2. In the temperature regime 413 K ≤ T ≤ 707 K the experimental rate constant was found to be










The reaction proceeds both via direct H-atom abstraction by CH2(X) and via thermal excitation of CH2(X) to the low-lying singlet state (a1A1) followed by fast consecutive reactions of CH2(a). The contributions due to thermal excitation and singlet reaction were evaluated for the present work as well as for a recent study of the reactions of CH2(X) with a series of other hydrocarbons. Corrected rate constants kT for the direct reactions of CH2(X) with the reactants HR = CH4 (1), C2H6 (2), C3H8 (3), n-C6H14 (4), i-C4H10 (5), and CH3CHO (6) in the temperature range 296 K ≤ T ≤ 707 K were found to be










The activation energies for the reactions studied are described by an Evans Polanyi type relation. Arrhenius expressions are proposed for the rate constants of H-atom abstraction by CH2(X3B1) from primary, secondary, tertiary, and aldehydic C -H bonds. The results are compared to the isoelectronic reactions of O(3P).

Kinetics of the Reactions between CH2(X̃3B1)-Radicals and Saturated Hydrocarbons in the Temperature Range 296 K ≤ T ≤ 707 K

Utilisation du methane, de l'ethane, de l'isobutane, de l'ethylene et du propane. Les radicaux CH 2 (a 1 A 1 ) sont generes par photolyse laser de CH 2 CO a λ=308 nm en presence de diverses concentrations d'hydrocarbures. Mesure des rendements en CH 2 (X~ 3 B 1 ), produits par conversion intersysteme, par LMR. Mecanisme. Cinetique

The Contributions of Intersystem Crossing and Reaction in the Removal of CH2(ã1A1) by Hydrocarbons Studied with the LMR

The elementary reactions of NH(a1Δ) with N, O, and NO and the reactions of NH(X3Σ−) with N, O and NO were studied in a quasi static laser flash photolysis cell at room temperature (T=298T) and low pressures (15≤p/mbar≤20). NH(a) was produced by HN3 laser photolysis at λ = 248 nm. NH(X) was obtained from the fast quenching of NH(a) with Xe. The O atom source was the NO + N reaction ([N]0>>[NO]0), with N atoms formed in a microwave discharge of N2/He. NH(a), NO(X) and the primary products NH(X), OH(X) and NO (X) were detected by pulsed laser induced fluorescence (LIF). The absolute N atom concentrations were determined via the reaction of N with NO. Time resolution was achieved by time delay between photolysis and probe laser pulses.



For overall depletion:










the following rate constants were obtained: k1, = (6.0±1.5)·1011 cm3/(mol·s); k2 = (5.6±2)·1012cm3/(mol·s); and k3 = (1.8±0.2)·1013 cm3(mol·s).



By fitting the NH(X) concentration profiles, determined experimentally, with computer simulations, the following rate constants for quenching channels were obtained: k1q = (6.0±1.2)·1011 cm3/(mol·s) and k2q = (1.2±0.3)·1012cm3/(mol·s). For the reaction pathways of reaction (2):

H. Gg. Wagner

Papers

The Surface Growth Phenomenon in Soot Formation

Direct Kinetic Studies of the Reactions Br + CH3OH and CH2OH + HBr: The Heat of Formation of CH2OH

Kinetics of the Reactions between CH2(X̃3B1)-Radicals and Saturated Hydrocarbons in the Temperature Range 296 K ≤ T ≤ 707 K

The Contributions of Intersystem Crossing and Reaction in the Removal of CH2(ã1A1) by Hydrocarbons Studied with the LMR

Elementary reactions of NH(a1Δ) and NH(X3Σ) with N, O and NO