Micro-explosion and burning characteristics of a single droplet of pyrolytic castor oil

In the study, castor oil is produced by thermal pyrolysis and its pyrolysis reaction and oxidation reactions are investigated using thermal gravimetric analysis. The results showed that the main pyrolysis and oxidation reactions occur in the temperature between 100 and 500 °C. The maximum weight loss occurs between 100 and 320 °C. Its non-volatile components may be ignited at about 500 °C and the residue is only about 0.18% of the original weight of the pyrolytic oil. The suspended droplet experimental system is also used to explore the micro-explosion phenomena and combustion modes of castor pyrolytic oil under different ambient temperatures (350 °C, 450 °C and 550 °C). The pyrolytic oil of castor seeds is a multi-component fuel and therefore has a wide boiling range. It results in a complex process during the heating process and the micro-explosion occurs, causing the droplet surface distortion. According to the timing and strength of the micro-explosion, there are three different stages: low intensity micro-explosion in the first stage, high intensity micro-explosion in the second stage and medium intensity micro-explosion in the last stage. After strong micro-explosion occurred in 550 °C ambient temperature, it will release more volatile vapor and the flammable mixture will form a non-premixed flame wrapping droplets after it is ignited in high temperature environments. During the combustion process of the droplet, the micro-explosion occurs continuously, but the droplet still maintains the appearance close to a sphere. The droplet rapidly evaporates and the flame wraps the droplet. In the latter period of the droplet combustion, volatile components have been completely evaporated, the residual solid particle will continue burning, and there is almost no residue after burning.