Microexplosion and ignition of droplets of fuel oil/bio-oil (derived from lauan wood) blends

Vaporization, microexplosion and ignition characteristics of a single droplet of pyrolysis bio-oil/fuel oil blends were examined using a suspended-droplet heating device. The bio-oil used in the experiment was produced from the fast pyrolysis process of lauan (shorea) wood, which is of low heating value, and high water as well as oxygen contents. The heating temperature (ambient temperature) and the mixing ratio of bio-oil/fuel oil blends were varied in the experiment. Two kinds of fuel oil were adopted, i.e., diesel and heavy fuel oil (HFO). The droplet evaporation, microexplosion and ignition behaviors were recorded by a high-speed video system. Meanwhile, the temperature histories (droplet and ambient temperatures) were measured by two K-type thermocouples in the heating process. For pure bio-oil, it was found that at the lower ambient temperature, 300 °C, random behavior (including expansion, bubbling, ejecting, and swelling) and microexplosion could be observed but ignition did not occur. However, at the higher ambient temperature, 500 °C, random behavior, microexplosion and ignition occurred for pure bio-oil and also for all cases of bio-oil/diesel blends. Random behavior and microexplosion occurred because the bio-oil contained many chemical compositions with various boiling points and water. For the bio-oil/HFO blends, ignition did not occur for low bio-oil contents (smaller than 50%) in the blends. However, when the bio-oil content was equal to or greater than 60%, ignition could occur but bio-oil/HFO-blends droplets took longer to finish burning compared with the bio-oil/diesel droplets.