Shock wave

Materials science

Mineralogy

Extinction (optical mineralogy)

Adiabatic flame temperature

Radiative transfer

Scaling

Thermodynamics

Physics

Organic chemistry

Mathematics

Optics

Vaporization

Molar absorptivity

Combustion

Combustor

Environmental science

Geometry

Chemistry

Mechanics

Proceedings of the Combustion Institute

A recent set of experiments carried out onboard the International Space Station (ISS) have shown that large n-alkane droplets, after the radiative extinction of the visible flame, can burn quasi-steadily in a low-temperature regime, up to a diffusive extinction accompanied by the formation of a vapor cloud. The experiments have also demonstrated that small droplets are unable to exhibit radiative extinction, but instead burn to completion or disruptively extinguish. In this work, we applied a mathematical model able to reproduce the experimental data in terms of vaporization rates, standoff ratios, extinction diameters. A detailed kinetic mechanism (with ∼450 species and ∼17,000 reactions) was taken into account, in order to correctly reproduce the low-temperature combustion regime. The role of several parameters (initial diameter of the droplet, composition of the gaseous environment, and pressure) on the extinction of the hot-temperature flames was numerically investigated. Predictions are found in good agreement with experimental measurements, showing that only droplets with an initial diameter larger than a critical diameter undergo radiative extinction. A linear relationship between the squared critical diameter and the molar fraction of oxygen in the atmosphere was found and demonstrated on the basis of scaling arguments.

Flame extinction and low-temperature combustion of isolated fuel droplets of n-alkanes