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Hexamethyldisiloxane (HMDSO) is one of the main impurities in the syngas produced from sewage and landfill plants. In order to utilize this syngas or control the characteristics of the generated silica particles, it is crucial to understand the chemical kinetics of HMDSO combustion. This study investigated the process of HMDSO combustion using synchrotron radiation mass spectrometry (SRMS), gas chromatography (GC), and ReaxFF molecular dynamics simulations. First, the force field used for ReaxFF simulation was validated by comparing the energies of different bond lengths, bond angles, and dihedral angles with the ones from DFT calculations. Good agreements were found. Then, ReaxFF simulations of HMDSO combustion with this force field were conducted under various conditions, which include different equivalence ratios (0.67, 1.0, and 1.5) and temperatures ranging from 2000 to 3500 K. The oxidation characteristics of HMDSO were analyzed, including the evolution of gas products and particle formation. Finally, based on the results from experiments and ReaxFF simulations, the reaction pathways, reaction lists, and reaction kinetics data during HMDSO combustion were obtained. A detailed reaction mechanism was proposed and validated by applying it in modeling the H2/HMDSO/O2 combustion systems. The temperature and part of the gas products such as CO and CO2 as well as SiO could be well predicted. [ABSTRACT FROM AUTHOR]

Silica nanoparticles have been widely applied in many fields due to their excellent properties. SiO2 generation is crucial for silica particle formation, but in a swirling reactor the SiO2 generation is still unclear. In this study, numerical simulations are performed to investigate the SiO2 generation and distributions of temperature and velocity during silica particle synthesis using a swirling reactor. A computational model is first developed to describe the heat and mass transport in the swirling turbulent flame. Simulation models are validated with experimental data in the case without SiO2 chemistry. Then, effects of the fuel velocity and swirl number on SiO2 generation are investigated. Results show that most of the SiO2 molecules are generated in the region far away from reactor inlets and a relatively high SiO2 generation efficiency is obtained for a fuel velocity of 32.7 m/second. Distributions of the flame temperature, velocity and SiO2 concentration are found to vary with the swirl number and high chemical reaction rates for SiO2 generation are obtained when a swirl number of 0.5 is employed. Uncertainty analysis shows that the average relative errors of the results from different models are within 18%. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of deposition surface shape on temperature distribution of fused silica glass by SiCl4 chemical vapor deposition and performs the optimization of deposition surface shape to obtain the glass with a small temperature gradient. The computational model is first developed to describe the complicated physical and chemical phenomenon in the system. Numerical simulations are then performed to evaluate the effects of SiCl4 injection position on flame characteristics and SiO2 deposition rate. It is found that the SiO2 deposition rates with the unimodal, uniform, and bimodal distributions are obtained when SiCl4 is injected from the central, secondary layer and fourth layer nozzles, respectively. The deposition surface shape is mainly determined by the gas temperature gradient and particle number density near the deposition surface. Thereafter, the temperature distributions in synthetic silica glass are presented for the cases with convex, flat, and concave deposition surface shapes. Large temperature gradients exist at the side of glass if the convex and concave surfaces are formed, although a high temperature uniformity is obtained in the center of glass for the convex deposition surface. The optimal surface shape that has a very small temperature gradient in glass is obtained by the optimization of deposition surface depth. [ABSTRACT FROM AUTHOR]

A comprehensive computational model is first presented, which is capable of describing multispecies turbulent reacting flow and particle formation and deposition. Then a detailed mechanism for SiCl4/H2/O2 reaction system is proposed and applied to the prediction of a counterflow laminar diffusion flame. Good agreement in flame temperature is obtained between numerical results and experimental data, and the augmented 30-reaction SiCl4 submechanism in the detailed mechanism has a significant impact on the SiO2 formation rate. To employ the detailed mechanism in three-dimensional simulations, the reduction of reaction mechanism is performed to eliminate inconsequential species and reactions. The physiochemical process in a silica glass furnace is first simulated with the detailed mechanism to obtain realistic sample compositions. Then, the directed relation graph (DRG) method is employed to construct three comprehensive skeletal mechanisms by considering all accessed compositions in the fused silica glass synthesis, and further analyzethe governing chemical kinetics. The predicted total SiO2 deposition on glass ingot is found to depend on mechanism reduction, and the species SiCl and HOCl are important for the formation of SiO2 and OH. While only two species and seven reactions are removed from the detailed mechanism even though the reduction threshold error of 0.15 has been employed. It is also found that the number of important chemical species and reactions is significant only in a narrow region, which indicates a great potential in local adaptive mechanism reduction. Therefore, the dynamic adaptive chemistry (DAC) is used to generate a small locally valid skeletal mechanism. For the same accuracy in temperature and SiO2 mass fraction, DAC method obtains higher speedup factor than that of DRG method. [ABSTRACT FROM AUTHOR]