Combustion fundamentals of pyrolysis oil based fuels

The combustion behavior of emulsions of pyrolysis oil in commercial diesel oil was studied. The emulsions were different in terms of concentration and size of the dispersed phase. The study was carried out in a single droplet combustion chamber. The size of droplets varied between 400 µm and 1200 µm. They were suspended to a bare thermocouple and, hence, their temperature during combustion was measured. High-speed digital shadowgraphy was used to follow droplets evolution. The main features of the droplet combustion were recognized. The general combustion behavior of emulsions is intermediate with respect to pure PO and commercial diesel oil. Emulsion droplets underwent strong swelling and microexplosion phenomena. However, under the investigated conditions, the microexplosions were ineffective in destroying droplets. The size distribution of the dispersed PO droplets in the range 3–10 µm was not effective nor for determining the overall thermal behavior nor for the efficacy of the microexplosions. The homogeneous combustion phase resulted identical for emulsions and diesel oil despite the emulsions composition (i.e., concentration of oil, surfactant and co-surfactant, as well as the size of the oil droplets in the emulsion) and the different structure of the flame and also its time and spatial evolution.