Multi-scale optical diagnostics for marine diesel spray

This study explores diesel spray characteristics, focusing on atomization, spray evolution and fuel-air mixing, which impact engine performance, fuel efficiency, and emissions. Compared to the conventional diesel spray studies, a multi-scale hierarchical approach using high-speed optical techniques is applied to analyze multi-hole, single-hole and near-nozzle sprays, using Mie scattering, simultaneous Mie scattering and schlieren, and microscopic imaging. Experiments conducted in an optical spray and combustion chamber (OSCC) varied injection pressures (1200, 1600, 2000 bar), chamber densities (4.72–28.06 kg/m³), and temperatures (298 K, 413 K, 588 K). Key spray parameters, such as penetration, cross-sectional area, cone angle, and tip velocity are studied across three scales. Results show spray evolution is more influenced by injection pressure and chamber density than temperature, with evolution categorized into three stages: initial accelerating, momentum-driven, and decelerating. Injection pressure significantly impacts the initial stage, while chamber density affects the momentum-driven and decelerating stages. These findings provide valuable data for 1D and 3D spray model validation, enhancing the understanding of marine diesel sprays and aiding the design of more efficient, eco-friendly marine propulsion systems.