Abstract
The main objective of this experimental-observational study is to investigate the microexplosion phenomenon of small methanol-in-diesel emulsion droplets (50 to 150 mu m) under realistic enginelike conditions of high temperature and pressure. The microemulsion was prepared mixing 59 wt % diesel and 25 wt % methanol with 16 wt % 1-dodecanol as the surfactant, whereas the macroemulsion was prepared with 87.6 wt % diesel, 10 wt % methanol, and 2.4 wt % mixture of two surfactants. The emulsion droplets were generated using a nozzle with a size of 230 mu m and injected into a high-pressure chamber. The chamber is optically accessible and filled with nitrogen at a pressure of 50 bar and a temperature of 900 K. In this current observation, emulsion droplets in the size range of 50 to 150 mu m in a high-pressure, high-temperature environment did not exhibit the phenomenon of microexplosion even up to 11 ms, which is close to the timescales of relevance in practical diesel engines. This is attributed to the small timescale of droplet evaporation, which is not sufficient for coalescence of the dispersed droplets inside an emulsion droplet to occur. As coalescence is a precursor for the microexplosion, the droplet tends to evaporate before undergoing microexplosion. In addition, a strong convective environment may create internal circulation inside the emulsion droplets, further restricting coalescence of the dispersed droplets.