Bio-oil has a content of water as high as 15–30 wt% derived from the original moisture in the feedstock and the product of dehydration during the pyrolysis reaction and storage. The presence of water lowers the heating value and flame temperature, but on the other hand, water reduces the viscosity and enhances the fluidity, which is good for the atomization and combustion of bio-oil in the engine. Shihadeh and Hochgreb [7] compared the biooils of NREL (National Renewable Energy Laboratory, US) to those of ENSYN (Ensyn Technologies, Inc., CA) and found that additional thermal cracking improved its chemical and vaporization characteristics. The better performance and better ignition of NREL oil derived from its lower water content and lower molecular weight.