Evaporating spray characteristics of methanol-in-diesel emulsions

Abstract

The main objective of this study is to investigate spray characteristics of methanol-in-diesel emulsions from a common rail diesel injection system under evaporating conditions using Mie-scattering and shadowgraphy techniques. The spray characteristics were measured in an optically-accessible constant volume chamber filled with nitrogen at a pressure of 50 bar and temperature of 900 K. Injection pressures of 500 bar, 1000 bar, and 1500 bar were investigated. Three surfactants (Span-80, Tween-80 and 1-dodecanol) were used to make stable emulsions containing up to 25 wt% of methanol in diesel. Interestingly, the liquid-length of the methanol-in-diesel emulsion spray with 10 wt% of methanol using a mixture of Span-80 and Tween-80 as a surfactant is higher by around 25% as compared to that of the diesel spray, even though methanol is far more volatile than diesel. This is attributed to the higher boiling point of the surfactant used, as confirmed by experiments with a low boiling point surfactant, i.e., 1-dodecanol. Further, microemulsions of methanol-in-diesel were produced by using 1-dodecanol as surfactant, which facilitated increasing the percentage of methanol in the microemulsion to up to 25 wt%. The evaporating spray liquid-length is observed to be insensitive to the methanol percentage in the emulsion when 1-dodecanol is used as the surfactant. Vapor penetration of the emulsions were similar to those of the diesel sprays at similar injection pressures. Overall, the current study provides measurements of detailed spray characteristics of methanol-in-diesel emulsions at engine-relevant conditions.