Effects of fuel temperature on the characteristics of diesel liquid-phase sprays

A diesel engine is the most energy-efficient powerplant in agricultural machinery. However, the performance of cold start has been limited to the diesel fuel viscosity in the low-temperature environment. Fluidity deterioration has also inhibited diesel spray atomization and evaporation, leading to the low reliability of diesel engines. In this study, the backlight test was conducted to compare the variation in the spray macrostructure of high and low-temperature diesel under different working conditions. The digital image processing of the spray images was then carried out using MATLAB to obtain the macroscopic characteristic parameters of the spray. The test results showed that the much more outstanding impact on the injection volume was obtained in the diameter of the spray hole 0.12 mm with the various injection pressures at diesel temperature. The continuous viscous force slowed down the flow velocity of the fluid layer near the wall and then suppressed the diesel emission. Once the diesel temperature was lower than 0 ℃, the diesel temperature was reduced by the amount of injection. The diesel temperature decreased to enhance the viscous force among droplets at high injection pressure. The continuous ejection of diesel was then promoted under the action of kinetic energy and inertial force. The fuel injection amount increased with the decrease in diesel temperature. When the injection pressure was 75 MPa, the diesel temperature dropped to -20 ℃, compared with 38 ℃ diesel injection quantity increased by nearly 23.87%. The diesel temperature decreased under small pore size, leading to the increase of viscous force among droplets. There was an increase in the droplet size and the greater momentum of droplets. Thus, the radial development trend of diesel spray was weakened to enhance the axial movement. Furthermore, the spray penetration increased with the decrease of diesel temperature, whereas, the spray cone angle decreased. The diesel spray penetration increased by 39.89 mm at 0.70 ms when the diesel temperature decreased from 38 ℃ to -20 ℃. When the nozzle diameter was 0.28 mm, the injection pressure was less than 75 MPa, and the injection quantity decreased with the decrease of diesel temperature. More momentum of diesel was consumed to overcome the greater internal friction under the same injection pressure. The farthest distance to reach was weakened. Diesel temperature was reduced to decrease the spray penetration and spray cone angle. When the injection pressure was 75 MPa, the diesel spray penetration at -20 ℃ at 0.70 ms was 30.86 mm shorter than that at 38 ℃. The spray penetration of -20 ℃ diesel decreased with the increasing nozzle diameter at the same injection pressure, whereas, the spray cone angle increased. Secondly, there was a more prominent influence of diesel temperature on the macroscopic characteristics of the spray with the increase in injection pressure. The higher the injection pressure was, the more outstanding the shortening trend of spray penetration caused by the decrease in diesel temperature was. Therefore, the injection pressure and nozzle diameter can be expected to improve for better evaporation and gasification of diesel liquid phase spray at low temperatures.