The lower heating value (LHV) of bio-oils is typically 14–18 MJ/kg, which is much lower than that of petroleum fuels (41– 43 MJ/kg). It is attributable to the high oxygen content. However, the density of bio-oils is about 1.2 g/ml compared with that of petroleum fuels, which is 0.8–1.0 g/ml. Therefore, the volumetric energy density of bio-oils can reach 50–60% of that of petroleum fuels.
The bio-oils are usually directly measured for their high heating values (HHVs). The LHV can then be calculated by the following equation proposed by Oasmaa et al. [25]: