Three-dimensional numerical calculations and laser induced fluorescence experiments on vaporization and ignition of a methanol droplet supported on a fiber.

摘要

The dissertation discusses the results of numerical simulations and experiments on vaporization and ignition of methanol droplets. The numerical simulations are done for the vaporization and ignition of a methanol droplet in a microgravity environment. The experiments investigated the laser induced fluorescence of acetone inside methanol and propanol droplets vaporizing and burning in still air at room conditions.;The methanol droplet in the numerical simulations is supported from or suspended at the end of a fiber in a crossflow of air. Vaporization calculations, in absence of combustion, are done for entire droplet histories. For combustion simulations, calculations are stopped shortly after ignition.;The results of the numerical simulations are categorized as follows: (i) 325 K dry airflow over a 1 mm solid sphere or liquid methanol droplet at a Reynolds number of 100 and 50 atm pressure. The sphere or the droplet is supported on a fiber. The results study the flow influences of the support fiber. (ii) 1000 K dry airflow over supported 100 micron methanol droplets vaporizing at 50 atm pressure. These calculations study the various influences of the support fiber on droplet heating and vaporization. Capillary surface flows caused by temperature gradients are allowed. (iii) 1500 K dry airflow over unsupported and supported 100 micron methanol droplets with ignition in 50 atm pressure environment. Calculations are stopped shortly after ignition. The calculations study the influences of the support fiber on ignition times, flame propagation and distribution of various species formed during early combustion. (iv) High temperature flows over supported 100 micron methanol droplets vaporizing in humid air environments. These calculations study the influences of the support fiber on the distribution of condensed water.;These experiments study images of laser induced fluorescence of acetone inside vaporizing and burning methanol and propanol droplets. In absence of combustion, acetone is well mixed inside the droplet and images show only small variations in pixel intensity. Ignition and subsequent burning causes rapid changes in acetone distribution inside the droplet. Large shape variations are additionally observed in burning propanol droplets.