Fengyu Li

Nanofluids are attracting attention as future energy carriers owing to their high performance for improving combustion and heat transfer. In this study, the macroscopic characteristics of nanofluid jets in a subsonic gaseous crossflow were investigated by focusing on the influence of nanoparticle additives on the breakup process. Based on a distribution map of the image grayscale standard deviation, we propose an improved method to process transverse injection shadowgraphs. A simplified model of the transition mechanism from column breakup to surface breakup at a small Weber number was established. The effects of nanoparticles on the jet trajectory and column fracture position were analyzed according to the deviations from the pure liquid. To interpret the effects of the nanoparticles, a new nondimensional parameter was introduced into the empirical correlation of the column fracture position. The results indicated that at low concentrations of nanoparticles, the surface tension of the nanofluids increased slightly, while the viscosity increased significantly (by up to 23%). These changes in the physical properties had little effect on the breakup regimes or jet trajectory. Moreover, the nanoparticles promoted cavitation inside the liquid column, resulting in an additional primary breakup mode for the nanofluids. Consequently, the length of the column fracture was reduced by up to 20% compared with that of the basic fluid.

In this study, the spray and atomization characteristics of neat biodiesel, ethanol-biodiesel blends (BDEs), and neat diesel in a high-pressure common-rail injection system were investigated experimentally and analytically. Schlieren-type high-speed photography was utilized to capture the experimental images. The findings indicated that spray penetration and peak tip velocity decreased and the spray cone angle increased with increase in the ratio of ethanol in the blends. Two predictive models were used to generate data to compare with measurements of spray penetration and peak tip velocity. The empirical formula of equivalence ratio, Ohnesorge number, and Sauter mean diameter (SMD) were calculated to evaluate atomization levels.

This study was conducted to investigate the spray characteristics of n-butanol, using a diesel spray for comparison. Spray tip penetration and spray cone angle were tested and analyzed. A high-speed photographic system was employed to observe the spray evolution, and a common-rail system and constant-volume chamber were used to change the pressure. The results show that the n-butanol spray penetrates faster than the diesel spray while under the same conditions. The experimental trend lines support the axial development model constructed by Hiroyasu and Arai on the grounds of a similar proportional relation to time after the start of injection, and the empirical equations provide reasonable approximations to the experimental measurements of the spray tip penetration.