Effects of injection pressure and nozzle diameter and fuel property on spray characteristics of blended diesel fuel

The fuel spray performance and atomization quality played a fundamental role in optimization of combustion efficiency and exhaust emissions in internal combustion engines. In order to achieve better atomizing mode of diesel, the spray characteristics of diesel blending pine oil and PODE3-4 were experimental studied. A spray trial platform include the 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. To be specific, this study was conducted under the diesel mixed with 20% pine oil, and 10% or 20% PODE3-4 was then added based on the mixture of diesel and 20% pine oil. Then, the influences of injection pressure, nozzle diameter and fuel property on macroscopic spray parameters (including spray cone angle, spray penetration distance and fuel flow area) were investigated in detail. It can be observed from the experimental research results 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. The decrease of spray penetration velocity is faster in the early stage, and the decrease is slow in the middle and late period and the fluctuation is produced. For the same nozzle diameter (10 mm), the blended fuel had a longer penetration distance with the increasing of the fuel injection pressure from 100 to 160 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 160 MPa injection pressure was larger than that at 100 MPa. When increasing the penetration distance by 13% from 100 to 160 MPa, for each increase of 20 MPa, the spray cone angle increases averagely by 1°. The initial spray penetration velocity increases with the increase of the injection pressure, but the final spray penetration velocity is not very different. If increasing the injection pressure, the fuel area will also increase, and therefore, increasing the injection pressure can improve the spray characteristics of the fuel and improve the utilization rate of the air. When the nozzle diameter increased from 0.10 to 0.18 mm at the same injection pressure (160 MPa), the increment of nozzle diameter led to obvious increase of the spray cone angle and the penetration distance. During the spray evolution process, the mean spray cone angle increased by about 3°. The spray penetration distance increased by about 28% at the end of the injection. The spray penetration velocity of the large nozzle diameter is always greater than that of the small nozzle diameter. The fuel area increases with the increase of the nozzle diameter. However, excessive nozzle diameter will result in an increase in the amount of fuel injection, and it is not conducive to the broken atomization of fuel. In addition, analyses showed that the spray penetration distance, spray cone angle and fuel area increased slightly after a certain proportion of pine oil and PODE3-4 were blended 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 - pine oil- PODE3-4 blend would be significantly beneficial for enhancing the atomization quality of pure diesel, and also provide a valuable reference on the spray characteristics to choose an acceptable and appropriate alternative fuel for common rail diesel engine. © 2018, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.