Characterization of multi-hole nozzle sprays and internal flow for different nozzle hole lengths in direct-injection diesel engines

Abstract

Multi-hole nozzles have a wide range of application in the fuel supply system of modern diesel engines, although singlehole nozzles dominate basic internal flow and spray research. The parameters of the nozzle geometry are crucial factors that can alter the internal flow dynamics of the nozzle and the consequent spray behaviours. The novelty of this study lies in implementing the application of practical prototype mini-sac multi-hole diesel nozzles to experimental and numerical studies. The internal flow and spray characteristics generated by practical multi-hole (10-hole) nozzles with different sac wall thicknesses (0.4 mm, 0.6 mm and 0.8 mm) were investigated in conjunction with a series of experimental and computational methods using a constant injection quantity (2 mm 3 /hole). Globally, the analysis mainly concentrated on different nozzle flow dynamics, different injection processes and different spray morphologies. Specifically, the high-speed video observation method was applied to visualize the injection processes and the spray evolution of different nozzles inside a high-pressure vessel. Furthermore, numerical simulations were conducted to reveal the three-dimensional nature of the internal flow inside different configurations; this was instructive in helping us to understand better the mechanism behind the spray behaviours. The results indicate that intense cavitating, turbulent and spiral rotating flow patterns occur inside practical multi-hole nozzles, and the consequent sprays emerging from the nozzles are perturbed, asymmetrical and unstable in both the near field and the far field. Moreover, a decrease in the nozzle hole length can increase the effects of cavitation, turbulence, the void fraction and the axial and radial injection velocity components on the nozzle hole exit; this is accompanied by an intriguing longer injection duration, wider near-field and far-field spray widths, a lower injection rate, and overlapping or even shorter spray propagation. However, these changes are not linear, and different parameters have different sensitivities to the variation in the nozzle hole length.

Study on Effect of Nozzle Hole Length to Diameter Ratio on Near-Field Diesel Spray Characteristics at High Density Conditions

“…There have been few publications presenting flow characteristics from different nozzle hole lengths [12,13]. The computational fluid dynamics (CFD) simulations for different nozzle configurations were performed and described the flow behaviors inside the nozzles [14]. From the literature reviewed in spray diagnostics, it has been limited research works conducted the simultaneously imaging for vapor and liquid phase fuel spray particularly focusing on near nozzle region.…”

Experimental diesel spray characterization of the medium-duty injector with single- and multi-hole nozzle configurations under non-reacting, non-vaporizing conditions

“…As seen in Figure 8A, for the same operating condition, the SH injector (black circle) showed faster spray penetration than the MH injector (red triangle). In particular, the MH injector showed a smaller initial slope (d S/dt) than the SH injector, indicating that the MH injector exhibits a slower rate of effective nozzle flow area increase than the SH injector, as reported in several studies (Dong et al, 2017;Jin et al, 2020). Although the initial slope is quite different between the SH and MH injectors, the spray penetrations at the later stage show a linearly correlated trend.…”

Internal Flow and Spray Dynamics of Multi-Hole Nozzle

“…According to the theoretical foundation of Mie scattering, the scattered light intensity is a symbolic characteristic of the droplet size and fuel concentration. The spray contours can help elucidate the effects of ambient gas entrainment and interactions between spray plumes [26].…”