ASSESSMENT OF MICROEXPLOSION PHENOMENON OF METHANOL-IN-DIESEL EMULSION DROPLETS UNDER ENGINE-LIKE CONDITIONS

The microexplosion phenomenon of small methanol-in-diesel emulsion droplets (50 to 150 ¹m) under realistic engine-like conditions of high temperature and pressure was investigated. The microemulsion was prepared mixing 59 wt. diesel and 25 wt. methanol with 16 wt. 1-dodecanol as the surfactant, while 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 μm 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. Emulsion droplets in the size range of 50 to 150 μm 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 evaporated before undergoing microexplosion. Also, a strong convective environment may create internal circulation inside the emulsion droplets, further restricting coalescence of the dispersed droplets.