Combustion of silane-nitrous oxide-argon mixtures: Analysis of laminar flame propagation and condensed products

Abstract

The laminar burning rate, the explosion peak pressure, and the pressure rise coefficient have been measured for the first time for silane-nitrous oxide-argon mixtures using the spherically expanding flame technique in a constant volume combustion chamber. For these three parameters, the values obtained were higher than for hydrogen-nitrous oxide-argon and typical hydrocarbon-based mixtures. A maximum burning rate of 1800 g/m2 s was measured at 101 kPa, whereas under similar conditions, a maximum burning rate around 950 g/m2 s has been reported for hydrogen-nitrous oxide-argon mixtures. To better understand the chemical dynamics of flames propagating in SiH4–N2O–Ar mixtures, a detailed reaction model from the literature was improved using collision limit violation analysis and updated thermodynamic properties calculated with a high-level ab initio approach. The reaction model predicts the burning rate within 14% on average but demonstrates error close to 50% for the richest mixtures. The chemistry of the H–O–N system is important under all the conditions presently studied. The chemistry of the Si–H–O–N system demonstrates an increasing importance under rich conditions. In particular, the reactions (i) forming SiOx(s); (ii) describing the interaction of Si-species with N2O; and (iii) involving silicon hydrides, have an important role for the heat release dynamics. The condensed combustion products formed in the silane-nitrous oxide-argon flames were sampled and characterized using electron micrograph, electronic diffraction, energy-dispersive spectroscopy, and X-ray powder diffraction. For all equivalence ratios, silica spherical particles with a mean diameter in the range 200–300 nm were observed. In addition, for mixtures with Φ ≥ 2.2, silicon nanowires were formed. X-ray diffraction experiments showed that the silicon nanowires are composed of metal silicon characterized by a cubic structure (lattice parameter: a=5.425Å) with the Fm-3m space group.