Cool flames in space: experimental and numerical studies of propane combustion

Abstract

New results from experiments on propane + oxygen cool flame and two-stage ignitions in microgravity are reported. These include the occurrence of a “self-stabilized” cool flame that survives for more than 10 s, before dying away. Then, by integration of reaction–diffusion equations in a one-dimensional model, using a reduced kinetic scheme including very recent kinetic data for propylperoxy radical reactions derived by DeSain et al., simulations of these phenomena are presented and discussed. A validation of the reduced mechanism is given first, by simulation of multiple stage ignitions in closed vessels under spatially uniform conditions. The model is used to obtain a detailed spatial structure for temperature and selected chemical species during the development of cool flames, simulated with heat and mass diffusion in 1-D. Also included are novel approaches to the simulation of pressure change in a spherical vessel and the light output from CH 2O ∗ chemiluminescence. The onset and spatial growth of the cool flame, and its ability to stabilize for a reasonable interval, is traced to the interaction between the elementary reactions that govern the negative temperature coefficient of reaction rate and the temperature field that is controlled by thermal diffusion to the reaction vessel walls. The vessel surface was assumed to be chemically inactive.