Stability of spray combustion for water/alcohols mixtures in oxygen-enriched air

The feasibility of burning fuels that are heavily diluted with water was evaluated. This concept could potentially be utilized to directly generate steam for a variety of applications, including power generation and enhanced oil recovery. Two water-soluble fuels, ethanol and 1-propanol, were heavily diluted with water and sprayed into a swirl-stabilized burner and the blow-off limits were obtained to identify the flame stability. The blow-off limit was experimentally determined as the lowest O-2 concentration where a flame could exist under a given oxidizer flow rate. For the present experimental system, stability maps were determined as a function of fuel concentration and oxidizer flow rate for different types of nozzles and both alcohols. Contours of temperature and overall fuel mass fraction in the droplets were obtained for a flame burning 15 wt% ethanol in an oxidizer of 50% O-2 and 50% N-2. The results revealed that preferential vaporization of ethanol over water plays an important role in enhancing flame stability. To further understand this, a model of bi-component droplet vaporization was employed for both the diffusion limit and distillation limit modes of liquid mass transfer. The results confirmed the preferential vaporization of ethanol and demonstrated that it is necessary to account for the non-ideal solution behavior of the alcohol-water mixture to appropriately model the vaporization process. The model also demonstrated that for this experimental system, droplet vaporization was better characterized by the distillation limit mode with enhanced mass transfer by convection. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.