Fluid motion and heat transfer in an ASTM-E659 apparatus

In this study, experimental measurements and three-dimensional numerical simulations were used to characterize the non-reactive gas motion and mixing inside the flask of our laboratories’ Autoignition Temperature (AIT) facility based on the ASTM-E659 standard. Downward plumes of cool air enter through the open top of the flask, through the neck, and into the spherical vessel. This creates a single dominant toroidal vortex that transports fluid upwards along the walls and downward along the center line. Increasing the height of the flask holder caused the average temperature to increase and the magnitude/frequency of fluctuations to decrease. Studies of fuel-air mixing of ethene (C2H4), n-hexane (nC6H₁₄), and n-dodecane (nC₁₂H₂₆) found that the lighter fuels more readily diffuse into air whereas the heavier fuels are more strongly influenced by buoyancy effects and take longer to mix. Further, in some cases the mixing time will be comparable to the time to ignition and long ignition times may result in significant quantities of fuel molecules escaping from the open top of the flask.