The primary purpose of this study is effect of bio-diesel fuel by the irradiation of the ultrasonic energy. The experiment was depending on the mixing ratio of the bio-diesel fuel and the amplitude of ultrasonic energy. And each fuel proceeded an 1H-NMR experiment. Accordingly, in this study, i analyzed the chemical properties and combustion characteristics of the reformed fuel. The results of the analysis have the following correlation.
(1) Irradiation of the ultrasonic energy is reduced of about 0.6% of the aromatics. And the ratio of aliphatic increased.
(2) When the irradiation time of ultrasonic energy increase, the Hα was reduced about 21.48%. The Hd is increased of about 3.63% and the HO is reduced of about 1.66%.
(3) After HC of a about 0.71% was increased, a about 0.59% is reduced. The HC is mainly composed of methylene.
(4) When the amplitude of ultrasonic energy is high, about 0.23% of the aromatic, about 1.15% of the HO and about 7.40% of the HC were reduced. On the other hand about 0.71% of the HC2 and about 1.97% of the were increased.
(5) The heating value form the symmetry with the Branch Index(BI), the aromatic and Hα. When the amplitude of ultrasonic energy is high, the improving effect is enhanced. Accordingly the heating value is also increased.
(6) Cetane number is correlate with Branch Index(BI), aromatic and Hα. So, the change of molecular structure is influenced on the cetane number. Therefore, when the amplitude of ultrasonic energy is high, the cetane number is increased.

Thus, Ultrasonic energy changes the molecular structure of the fuel to a the various of factors(Cavitation, Intentionality, radiation pressure, etc.). Ultrasonic devices supplement bio-diesel''s faults and will improve the engine performance.