In the context of global efforts to pursue carbon neutrality, the research on the application technology of methanol fuel in internal combustion engines has ushered in a new peak. In order to provide a theoretical basis for the development of direct injection methanol engines, the spray characteristics of methanol with high-pressure direct injection were studied. Based on the visualization experimental device of constant volume vessels, the diffused background-illumination extinction imaging (DBI) and schlieren methods were applied to examine the distinctions in the evaporating spray properties between methanol and diesel under different injection pressures and ambient temperature conditions. Furthermore, aiming to maximize the potential of methanol fuel in compression ignition engines, under the premise that the alternative fuel can obtain the same total fuel energy as diesel, two different injection strategies of methanol were proposed and evaluated through the coordination of the nozzle hole diameter, injection pressure and injection duration. It reveals that it is easier for methanol spray to evaporate because of the lower boiling point, which results in a shorter spray tip penetration and wider spray angle compared with those of diesel, especially under the middle-level ambient temperature (600 K) condition. These deviations are also observed under different injection pressure conditions. However, affected by the lower energy density, the strategies of injecting the same fuel energy of methanol with that of diesel prolong the methanol spray tip penetration, enlarge its spray area and sacrifice the methanol evaporation performance. It is necessary for the geometrical design of the combustion chamber to coordinate with the hole diameter and injection pressure selection to deal with the huge distinctions in the spray characteristics between methanol and diesel fuel.

This investigation employed the diffused back-illumination (DBI) technique to analyze the spray characteristics of hydrotreated vegetable oil (HVO) fuel at three injection pressures and compared them with conventional diesel fuel. The results showed that as the injection pressure increased, the peak injection rates of both the HVO and diesel increased. At injection pressures above 120 MPa, the injection rates of both fuels were nearly identical, though differences were observed at lower pressures. Increasing the injection pressure reduced the injection delay. The HVO fuel exhibited a shorter spray tip penetration, lower equivalence ratio, larger spray angle, and spray volume, but its spray angle stability was lower than that of diesel. The ambient gas entrainment rate primarily occurred in two stages, significantly influenced by the spray breakup development stage. For diesel sprays, the injection pressure mainly affected the equivalence ratio near the nozzle with minimal downstream impact. Dent’s model provided better predictions of the penetration distance for diesel, while Hiroyasu’s model was more accurate in predicting the penetration distance of the HVO at 120 MPa and 180 MPa. Inagaki’s model performed better in predicting the spray angle for diesel, whereas Hiroyasu’s model was more accurate for the HVO spray angle predictions. Through this research, a better understanding of the spray characteristics of green fuels will be achieved, providing a reference for the design and optimization of new generation engines.

Faced with dual challenges of “carbon neutral” and emission control, fossil fuel-based internal combustion engines need to explore new ways and technical paths to reduce harmful emissions and Carbon dioxide emissions simultaneously. Fuel injection process is playing a significant role not only in traditional engines but also in new low/zero carbon engines. Multi-hole nozzles have a wide range of applications in the fuel supply system. While the accepted spray study work and jet break-up models are usually developed under the quasi-steady-state of fuel injection by a single-hole nozzle. There are rare models that can describe the whole break-up processes of multi-hole nozzle spray, including complex internal flow factors, plume interaction, and the effect of start/end of injection. In this chapter, characteristics of spray morphology, evolution processes, and evaporation characteristics, emerging from the practical diesel multi-hole nozzles, were discussed and analyzed during the transient injection processes in detail. Moreover, the relationship between multi-hole nozzle internal flow properties and the corresponding spray behaviors was investigated by numerical simulation method systematically. Therefore, multi-hole spray modeling processes under engine operating conditions and the optimized design of diesel multi-hole nozzles are expected to get some benefits and clues from the current results.