Post-injection fuel dribble is known to lead to incomplete atomisation and combustion due to the release of slow-moving, and often surface-bound, liquid fuel after the end of injection. This can have a negative effect on engine emissions, performance and injector durability. To better quantify this phenomenon, we developed an image-processing approach to measure the volume of ligaments produced during the end of injection. We applied our processing approach to an Engine Combustion Network ‘Spray B’ 3-hole injector, using datasets from 220 injections generated by different research groups, to decouple the effect of gas temperature and pressure on the fuel dribble process. High-speed X-ray phase-contrast images obtained at room temperature conditions (297 K) at the Advanced Photon Source at Argonne National Laboratory, together with diffused back-illumination images captured at a wide range of temperature conditions (293–900 K) by CMT Motores Térmicos were analysed and compared quantitatively. We found a good agreement between image sets obtained by Argonne National Laboratory and CMT Motores Térmicos using different imaging techniques. The maximum dribble volume within the field of view of the imaging system and the mean rate of fuel dribble were considered as characteristic parameters of the fuel dribble process. Analysis showed that the absolute mean dribble rate increases with temperature when injection pressure is higher than 1000 bar and slightly decreases at high injection pressures (>500 bar) when temperature is close to 293 K. Larger maximum volumes of the fuel dribble were observed at lower gas temperatures (∼473 K) and low gas pressures (<30 bar), with a slight dependence on injection pressure.

Accurate experimental data are often needed to validate computational fluid dynamics models. These models regularly rely on experimental results from single-orifice axially drilled nozzles that do not fully represent real injectors, as the difference in inclination angles creates turbulent conditions at the nozzle outlet, consequences of which on the spray development are not yet fully understood. In this work, near-field visualization was done for two nozzle inclination angles in non-vaporizing conditions. Spray tip penetration, spreading angle, and axis angle fluctuations are reported. Three hypotheses are analyzed: liquid jet breakup mechanism, internal flow development, and cavitation. Experiments were carried out using n-Dodecane, testing a single orifice axially drilled and a three-orifice injector, from the Engine Combustion Network. The spray was observed with a diffused back-illumination technique and a long distance microscope, only visualizing the first 6 mm of spray tip penetration, for three injection pressures and four gas densities at ambient temperature. The multi-orifice injector produced a spray with wider spreading angle, which resulted in smaller penetration values. Additionally, higher spray axis angle fluctuations were observed for the multi-orifice injector, which increased for higher injection pressure and, to a lesser extent, with decreasing chamber density. Further analysis was performed with spreading angle fluctuations measurements, where results showed good agreement with spray axis angle fluctuations trends, implying that complex internal flow structures, and even incipient cavitation, could be present in the multi-orifice injector and be the cause of these spray axis angle fluctuations.

As legislations set very stringent environmental and fuel economy standards, researchers have pushed into a continuous development in all areas of the diesel engine. The recent evolution of the injection technologies has permitted to modify the fuel-delivery strategies. From what was a single pulse per injection event, modern systems allow to inject up to eight different times precisely per combustion cycle. In such sense, experimental results of the rate of injection and momentum flux could be useful for validation and improvement of computational models. Moreover, accurately quantifying the injected mass per pulse in a fuel–gas interface can provide data with more realistic engine-like conditions. To this end, this research presents measurements of the rate of injection and momentum flux for two simple multiple injection strategies: a pilot-main and a main-post. Boundary conditions included two rail and discharge pressures, two different pilot/post quantities and four dwell times. A new approach was employed to estimate the mass allocation with the momentum flux data, and results were compared to the rate of injection traces to verify the distribution calculated. On the results, signals for each pulse were successfully decoupled using its rising and falling edge. The shot-to-shot variability of the pilot/post injection was highly dependent on its transitory characteristics, and on the dwell time for post injections due to internal pressure waves. The injected mass per pulse was successfully measured as well in the momentum flux test rig, and the energizing time changed slightly to account for the different operation interfaces. Signals from both measurement campaigns showed a remarkable agreement when compared, ascertain the possibility of measuring the injected mass, and its allocation for multiple injection strategies, in the momentum flux test rig.