METHANE AND METHANOL DIFFUSION FLAMES IN SUPERCRITICAL WATER

Our interest in understanding supercritical-water oxidation as a process for the destruction of hazardous wastes has led us to examine hydrothermal diffusion flames that can ignite in supercritical water-fuel-oxygen mixtures. We injected pure oxy-en into water-methane and water-methanol mixtures at 275 bar, varying fuel concentrations from 1 to 50 mol % and temperatures from 380 to 510-degrees-C. Measurements of minimum fuel concentrations required for the spontaneous ignition of diffusion flames in supercritical water are reported. The flames ignite at methane or methanol concentrations as low as 6 mol % at temperatures near 500-degrees-C. The ignition-threshold concentrations rise as temperature is decreased to 400-degrees-C. Visual and shadowgraph video records reveal an insensitivity of flame height to diminishing fuel concentration. In contrast, both luminosity and average flame temperature vary strongly with fuel concentration. Flame structures are detectable long after flame luminosity is no longer visible, with measured average flame temperatures within a few hundred degrees of ambient.