Unraveling combustion chemistry of dimethyldiethoxysilane. II. A comprehensive study on the laminar flame propagation of ethoxysilane flame synthesis precursors

Abstract

The ethoxysilane family is a popular precursor family for SiO₂ nanoparticle flame synthesis, understanding their combustion characteristics and reaction mechanisms are essential to control the synthesis performance. However, there is a scarcity of fundamental combustion studies on ethoxysilane precursors, particularly regarding fuel decomposition and oxidation under flame circumstances. This work, as the second part of a serial work on the combustion of dimethyldiethoxysilane (DMDEOS) which is a representative ethoxysilane precursor, reports an experimental, theoretical, and kinetic modeling investigation on its laminar flames. Laminar burning velocities of the DMDEOS/air mixtures are obtained using the spherically propagating flame method at the initial pressure of 1 atm and initial temperature of 423 K, and equivalence ratios from 0.7 to 1.5. The H-abstraction reactions of DMDEOS by H, CH₃, and OH, followed by the subsequent isomerization and β-scission reactions of fuel radicals, are theoretically investigated using ab initio quantum chemical calculations and rate constant calculations. A kinetic model of DMDEOS combustion incorporated with the present theoretical results is developed and validated against the new data. The rate of production analysis and sensitivity analysis indicate that the CH₃SiOOH plays an important role in the laminar flame propagation of DMDEOS/air mixtures, and the relevant reactions exhibit significant sensitivity for the laminar flame propagation of DMDEOS. Additionally, the consumption of CH₃SiOOH is the main source of key species that are essential for molecular growth. The modified fictitious diluent gas method is adopted to provide insights into the fuel molecular structure effects from the comparison with diethoxymethane (DEM), which has the same molecular skeleton length as DMDEOS. The thermal effect plays a dominantly positive role in the slower laminar flame propagation of DMDEOS than DEM under stoichiometric and rich conditions, while the chemical effect exhibits a negative effect.