Abstract: The fuel spray performance and atomization quality played a fundamental role in promoting the level of combustion efficiency and exhaust emissions in internal combustion engines. In order to achieve better atomizing mode of diesel, we conducted experiments to study the spray characteristics of diesel blending pine oil. A diesel/pine oil spray trial platform was constructed to carry out a visual constant volume chamber and the high-pressure common rail test bench. The high-speed photograph technique was applied to systematically investigate the spray process of blended fuel. The study was conducted under the pine oil blending ratios of with 0, 20%, 40% and 50%, respectively. Then, the influences of injection pressure, ambient pressure and fuel property on macroscopic spray parameters (including spray cone angle, spray penetration distance and fuel flow area) were investigated. The results showed that at first, the spray penetration distance of blended fuel presented a certain degree of linear growth with the fuel injection, and then the increasing rate of the penetration distance decreased. On the other hand, it was observed that the spray cone angle was wider at the beginning of the spray development, and it gradually converged to a smaller and constant value. In general, the variation of the spray cone angle is stabilized during spray process. For the same ambient pressure (5 MPa), the blended fuel had a longer penetration distance with increasing the fuel injection pressure from 90 MPa to 150 MPa. And the effect of injection pressure on the spray cone angle according to the variation in injection pressure showed that the spray cone angle at a 150 MPa injection pressure was larger than that at 90 MPa of injection pressure. The percentage increased in the mean spray cone angle and penetration distance was 9.2% and 15%, respectively. When the ambient pressure increased from 3 MPa to 5 MPa at the same injection pressure (12 MPa), the increment of ambient pressure led to obvious increase of the spray cone angle as well as sharp decrease of the penetration distance. During the spray evolution process, the mean spray cone angle increased about 2.6°. The spray penetration distance decreased about 11 mm at the end of the injection. This indicated that the rise of ambient pressure had a significant effect on spray characteristics. In the range of experimental condition, good correlation was found between the spray penetration distance of blended fuel and the modified Hiroyasu's empirical equation. When injection pressure was 150 MPa and ambient pressure was 5 MPa, the effect of Reynolds number was greater than that of Weber number as blending ratios of pine oil increased by 50%. This suggested that the fuel viscosity played an important role in spray characteristics. The spray performance of blended fuel was basically similar to conventional diesel fuel with the variation of injection pressure and ambient pressure. In addition, analyses showed that the spray penetration distance, spray cone angle and fuel flow area increased slightly after blended a certain proportion of pine oil into diesel, which was very conducive to improve air and fuel mixture effect with pine oil. It can be concluded that investigating the spray characteristics of diesel and pine oil blends would be significantly beneficial for enhancing the atomization quality of pure diesel, and also provided a valuable reference on the spray characteristics to choose an acceptable and appropriate alternative fuel for common rail diesel engine.