Nikolai M. Rubtsov - Key Factors of Combustion: From Kinetics to Gas Dynamics

Springer International Publishing Switzerland 2017

Nikolai M. Rubtsov 1

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Abstract

The inhibition and promotion of non-thermal NCl3 flame by NOCl and H2, respectively, are explained. The crossover from the non-thermal mode of flame propagation to the thermal one is analyzed for NCl3He mixtures. Calculations based on a kinetic mechanism taking into account energy chain branching are performed, and qualitative agreement between the calculated and observed data is demonstrated. Nonlinear chain branching shortens the time needed for thermal ignition and increases the flammability of the combustible mixture. It is shown that the mechanism of reaction of NCl3 decomposition proposed above is in good qualitative agreement with experimental data. It is established that the conditions sufficient to obtain oscillating solutions are the following: (a) accounting for adsorptiondesorption of NCl3 on reactor walls, (b) accounting for nonlinear chain termination Cl + Cl23ou Cl + Cl21g , (c) accounting for energy chain branching. Therefore, accounting for processes of desorption of NCl3 from the reactor surface during oscillations and the change in a surface state leads to the occurrence of the oscillation modes in a numerical experiment, which are in qualitative agreement with experimental data.

The promotion of the branched-chain decomposition of nitrogen trichloride by molecular hydrogen additives manifests itself in a decrease in the induction period and the acceleration of initial reactant consumption. The emission spectrum of the H2 + NCl3 flame contains the intense bands of NCl (b1+ X3, v = 10, v = 01, and v = 00), and the bands of a hydrogen-free compound. The latter bands can be assigned to electronically excited NCl2 radicals formed in the H + NCl3 reaction. The promotion effect in the system studied should be due to the side reaction of linear branching. The occurrence of the H + NCl3 reaction via two pathways (NHCl + 2Cl and NCl2 + HCl) ensures the qualitative agreement between the experimental data and calculation.

Keywords

Nitrogen trichloride NCl3 (yellow very explosive liquid with 150 Torr vapor pressure under normal conditions) does not require any oxidizer to ignite. Because it is decomposition of individual substance, its detailed mechanism seems to be comparably simple. At the same time, the mechanism shows the very specific peculiarity of chain combustion namely a nonlinear energy branching. The features of thermal decomposition of NCl3 are considered in the following chapter.