Stability of Diesel/Water Emulsions: Experimental and Modeling Investigations

Diesel/water emulsions have several applications in the upstream and downstream petroleum industry. Diesel/water emulsions have been proposed as an alternative fuel due to their potential to emit a lesser amount of nitrogen oxides and particulate matter in the current models of compressed ignition engines. In the upstream petroleum research, diesel/water emulsions are used for the targeted delivery of several chemicals in deep reservoirs. The diesel/water emulsions are not very well understood despite their numerous applications. In this work, diesel/water emulsions were prepared using octylphenol ethoxylate as an emulsifier at different mixing times and speeds, varying surfactant concentrations, and using different water/diesel ratios. The emulsion stability was evaluated using a bottle test method, droplet size distribution (microscope), and rheological measurements. The bottle tests were mainly used to determine the emulsion stability, while the optical microscopic analysis was carried out to validate and understand the relation between the droplet size distribution and its impact on emulsion stability. It was found that emulsion stability not only depends on the concentration of surfactant, water, and diesel but also on mixing speed and time. The emulsion stability was enhanced by increasing the concentration of water, and the most stable emulsions were achieved when the water ratio was higher than 80 v/v%. The emulsion stability significantly increased when the mixing speed was increased up to 1200 rpm compounded with a mixing time of 20 min. An optimum surfactant concentration was noted to get the most stable emulsions ranging from 2.5 v/v% to 5 v/v%. The K-Star model was adopted in this study to predict the experimentally determined viscosity values. Modeling results showed that the predicted and measured viscosities were very close with minimal marginal errors. The excellent predicted viscosity values are demonstrated by the considerable root mean square error: 0.0873 and 2.5164 and mean absolute error: 0.0595 and 1.8675 for the training and testing dataset, respectively. The current study indicated that water to diesel ratio and mixing method could significantly affect the emulsion characteristics.