Internal combustion (IC) engines serve as power devices that are widely applied in the fields of transport, engineering machinery, stationary power generation, etc., and are evolving towards the goal of higher efficiency and lower environmental impacts. In this Editorial, the role of IC engines for future transport and energy systems is discussed, and research directions for advancing IC engine and fuel technologies are recommended. Finally, we introduce the 14 technical papers collected for this Special Issue, which cover a wide range of research topics, including diesel spray characteristics, combustion technologies for low- and zero-carbon fuels, advanced combustion mode, fuel additive effects, engine operation under extreme conditions and advanced materials and manufacturing processes.

This article presents a computational fluid dynamics study of the engine combustion network Spray G, focusing on the transient characteristics of the spray during the start of injection and the impacts of nozzle geometry details derived from the manufacturing process. The large-eddy-simulation method, coupled with the volume-of-fluid method, was used to model the high-speed turbulent two-phase flow. A moving-needle boundary condition was applied to capture the internal flow boundary condition accurately. The injector geometry was measured with micron-level resolution using X-ray tomographic imaging at the Advanced Photon Source at Argonne National Laboratory, providing detailed machining tolerance and defects from manufacturing and a realistic rough surface. For comparison, a nominal geometry and a modified geometry incorporating measured large-scale geometric features but no surface details were also used in the simulations. Spray characteristics such as mass flow rate, injection velocity, and Sauter mean diameter were analyzed. Significantly distinct spray characteristics in terms of injection velocity, spray morphology, and primary breakup mechanism were predicted using different nozzle geometries, which is mainly attributable to the realistic surface finish and manufacturing defects. The measured high-resolution geometry predicts a lower injection velocity, a wider-spreading spray, and an overall slower breakup rate with evident injector tip wetting compared to the ideally smooth nozzle boundary. This result implies that the manufacturing details of the injector, which are usually ignored in fuel injection studies, have a significant impact on the spray development process and should be taken into account for design optimization.