Ignition of n-propanol-air hydrothermal flames during supercritical water oxidation

A novel concept was applied for the in situ study of the ignition of n-propanol-air hydrothermal flames during supercritical water oxidation. An innovative experimental arrangement including NASA's supercritical water oxidation facility was used to study the effect of reactor and oxidant (air) temperature on the spontaneous ignition of hydrothermal flames. New data were obtained concerning time- and temperature-resolved profiles of n-propanol in hydrothermal flames. Transient temperature profiles were recorded and the sudden increase in the temperature was used to determine the onset of flame ignition. The optimal reactor temperatures for flame ignition (ignition delay ∼1 s) were determined as 380 °C (at oxidant temperature of 450 °C) and 420 °C (at oxidant temperature of 400 °C) with 20.7 MPa pressure and 1.5 mL/s oxidant (air) flow rate. The influence of buoyancy on ignition is also discussed in terms of Froude number. Time delays associated with the flame ignition at near-critical and supercritical environments as well as possible routes towards their diminution are elaborated. The ignition mechanism of n-propanol-air hydrothermal flames together with the ignition maps have been proposed for the first time.