MACROSCOPIC SPRAY CHARACTERISTICS OF DIESEL AND BIODIESEL-DIESEL BLEND: AN EXPERIMENTAL COMPARISON

Abstract

The qualitative aspects of the fuel spray particularly spray length and cone angle play a significant role not only in the temporal sequence of clean and efficient combustion, but also in the control of engine exhaust emissions and efficiency optimization. This paper investigates the effect of injection duration and ambient pressure on spray development, spray tip penetration (L) and cone angle ( β ) of biodiesel-diesel (20%/80%:v/v) blend (B20) and diesel, and hence compares the quality of the fuels. Both ‘L’ and ‘ β ’ play a key role in the fuel evaporation and mixing of fuel with air in the combustion chamber. It was found that the injection pressure, spray tip penetration and cone angle of the fuels increased with the increase in injection duration. Furthermore, the injection pressure of B20 was higher than that of diesel because of its higher incompressibility, which increased the droplet momentum and tip penetration. The ambient pressure displayed a stronger impact on ‘L’ and ‘ β ’ of the fuels, compared with injection duration. The ‘L’ was increased, while ‘ β ’ decreased with the decrease in P amb due to the decrease in resistance to penetration velocity. The shapes of spray images of two fuels were almost similar. However, B20 exhibited larger ‘L’ and ‘ β ’ due to higher initial velocity and mass of droplet, compared with diesel. This indicates that relative to diesel fuel, B20 has a stronger impact on the spray performance, and thus improves both ‘L’ and ‘ β ’. During the earlier phase of time after start of injection, the relative difference between two fuels in terms of their spray tip penetration was smaller. This difference augmented, and then became roughly stable. Before the commencement of a comparatively steady phase of time after the start of injection, the test fuels revealed an appreciable relative difference in terms of their ‘ β ’.