Rate constants of elementary reactions involving unimolecular steps can be calculated from molecular data in a most general way by solving appropriate master equations. The conventional numerical solution requires rather a fine discretization applied over a sufficiently large energy range to achieve a reasonable accuracy. This leads to linear but very high‐dimensional systems of differential equations. We propose a quasi‐spectral method that uses Gaussian radial basis functions to establish a low‐dimensional linear model to speed up the numerical integration. The combination with an iterative adaptation provides a further improvement of computational efficiency. The suggested approach is illustrated and exemplified by means of the unimolecular decomposition of 2,3‐dihydro‐2,5‐dimethylfuran‐3‐yl, an intermediate radical occurring in the pyrolysis and oxidation of 2,5‐dimethylfuran. A comparison of the conventional and the proposed method is presented to validate the novel approach and to demonstrate its performance.
The problem of Detonation to Deflagration (DDT) is revisited. A stoichiometric hydrogen/oxygen combustion system is considered. The study focuses on the investigation of the system solution in the thermo-chemical state space of the system. The Σ model is implemented to study the flame acceleration and DDT in 1D formulation. The model was suggested to take into account wrinkling of the flame surface. In this way, the problem becomes treatable numerically even with the detailed mechanism of chemical kinetics and with detailed models for molecular diffusion. In order to treat and integrate the model a recently developed numerical scheme to deal with very stiff systems both in time and in space is introduced and applied. Typical system solution profiles of the ignition, quasi-deflagration, flame acceleration, DDT and detonation stages are considered to study the structure of the flame front in the system thermo-chemical state space. The results of computations show that at the stages of the ignition, deflagration and acceleration the flame structure in the state/composition space moderately depends on Σ, however, significant influence shows up during later stages of the flame acceleration and DDT. Moreover, the path of the solution in the detonation regime significantly deviates from that of deflagration. This means that accurate and quantitative study of the DDT is not possible without reliable mechanisms of chemical kinetics able to describe the system state space during the transient.
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