Liquid-phase dynamics during the two-droplet combustion of diesel-based fuel mixtures

The liquid-phase processes occurring during fuel droplet combustion are important in deciding the behaviour of the overall combustion process, especially, for the binary fuel droplets. Hence, understanding these processes is essential for explaining the combustion of the binary fuel droplet. However, experimental investigation of such processes is not easily accomplishable due to the very short period of time available for tracking them within the finely small fuel droplet. In the present work, a high speed imaging and subsequent image processing leading to quantitative analysis of the binary fuel droplet combustion including liquid-phase dynamics are performed. Two categories of binary fuels – in which diesel is the base fuel – are prepared and utilized. The first category is biodiesel/diesel and bioethanol/diesel blends, while the second category is the water-in-diesel and diesel-in-water emulsions. Specific optical setup is developed and used for tracking droplet combustion. The resulting magnification of the droplet images is up to 30 times the real size, offering the possibility of droplet interior visualization at high imaging rates up (to 40,000 fps). With the aid of this setup, spatial and temporal tracking of nucleation, bubble formation, puffing, microexplosion, and secondary atomization during the combustion of two adjacent binary fuel droplets are performed. The burning rate constants are evaluated and found to have the same trends as the isolated droplet combustion. However, the ratio of the droplet burning rate constant of the interactive droplet combustion to that of the isolated droplet combustion is higher than unity. This is the same for the nucleation rate within the interacting fuel droplets.