Emulsification is an economic route for the applications of pyrolysis bio-oil in diesel engines and industrial furnaces and heating. The oxidative reaction interaction of a number of bio-oil/diesel emulsified fuels at various bio-oil contents and bio-oil-to-emulsifier weight ratios (i.e. B/E ratios) is analyzed to provide a basis for the applications of pyrolysis bio-oil. The commercial Atlox 4914 is used as the surfactant, while a thermogravimetric analyzer is employed in the analysis. The interaction phenomena are obviously observed during the oxidative reaction of the emulsified fuels. The interaction can be partitioned into a weak antagonistic zone (<= 210 degrees C) and a significant synergistic zone (>= 210 degrees C). In the synergistic zone, the oxidation of the fuels is enhanced and the maximum interaction occurs at about 380 degrees C. A dimensionless parameter termed the synergistic index (SI) is introduced to measure the interaction degree. An increase in the bio-oil content intensifies the interaction up to around 11%, whereas increasing the B/E ratio lowers the SI value. Meanwhile, an opposite trend in the fuel reactivity and burnout temperature is exhibited. The obtained results are able to provide a strategy for the preparation of bio-oil/diesel emulsified fuels to intensify their fuel reactivity and applications in industry. (C) 2019 Elsevier Ltd. All rights reserved.