ID 18

Evaporation characteristics of binary alkane-ethanol blends investigated by droplet drag phase measurements using Raman spectroscopy

 

Abstract:

Climate-affecting emissions in addition to increasingly stricter environmental legislation urge for a growing usage of renewable fuels. Due to its potential to decrease pollutant emissions while simultaneously improving engine efficiency, ethanol is one of the most promising green fuels. Even though mixtures of gasoline and ethanol are already in use, the evaporation process of fuel blends is still insufficiently characterized. The particular occurrence of component-wise evaporation challenges the development of the engine combustion process due to inhomogeneous carburation. Still, available sources for experimental validation focus on lying or levitated droplets. Thus, detailed information of air enrichment in the drag phase at small droplet spacing and the influence of turbulences close to the droplet are missing out. Therefore, the emphasis of this work is the experimental evaluation of the component-wise evaporation of free falling droplets consisting of various binary blends of ethanol and alkanes. A high-resolution Raman setup is used to detect the drag vapor phase between droplet chains with varying distance between droplets. Combined with a fast trigger system the vapor phase behind the falling droplets is temporally and spatially analyzed in the direction of the falling droplets. The Raman signals of the components overlap additively and differ considerably. Therefore, the concentration ratio in the vapor phase behind the droplet is determined. To ensure engine-like conditions the droplet size is kept below 60 µm. The evaluation displays component-wise transfer into the gas phase dependent on temperature, falling distance and the component ratio inside the droplet. Furthermore, the results indicate a decrease of the more volatile component at the droplet surface with increasing droplet temperature at selected component ratios.