Enhanced mixing and combustion through ducted fuel injection

This presentation introduces ducted fuel injection (DFI), a simple and effective mechanical approach for improving fuel/charge-gas mixture preparation within diesel-engine combustion chambers, with the ultimate goal of reducing emissions while increasing efficiency. In DFI, each fuel spray is injected along the axis of a small cylindrical duct, promoting more complete local premixing at or near the duct exit, where autoignition occurs. The presentation summarizes the development of DFI technology at Sandia, beginning with proof-of-concept experiments in a constant-volume combustion vessel, continuing through testing in a single-cylinder optical engine, to a recent study employing a retrofitted heavy-duty multicylinder engine. The underlying physical mechanisms that enable DFI to work are discussed, as well as potential performance-limiting factors. The presentation concludes with a summary of promising initial progress toward achieving low-emissions, high-efficiency, "lean mixing-controlled combustion" with DFI. Such advancements diversify humanity's portfolio of technology options available for efficient, clean power, and they can enable pragmatic solutions where electrification or switching to carbon-free fuels is too costly.

Shock-Driven Multiphase Flows under Extreme Conditions: From Supercritical Fuel Mixing to Hypersonic Aerodynamics

Shock-driven multiphase flows play a critical role in high-speed propulsion systems, including fuel injection and combustion in high-pressure, high-temperature environments, multiphase detonation, and the interaction of hypersonic vehicles with atmospheric droplets. These flows involve complex interactions among shock waves, interfacial instabilities, droplet breakup, phase change, and fluid mixing across a wide range of length and time scales, presenting significant challenges for experimental characterization and predictive modeling. This presentation will introduce a multiscale computational framework integrating molecular dynamics (MD) and direct numerical simulations (DNS) to investigate shock-driven droplet dynamics under extreme thermodynamic conditions. The transition from subcritical to supercritical conditions, where changes in interfacial properties, phase behavior, and molecular transport alter droplet breakup, evaporation, and fuel–oxidizer mixing will be shown. The presentation will also examine reacting shock-driven droplet interactions under high-pressure and supercritical conditions, focusing on the coupling among shock dynamics, phase change, chemical reactions, and mixing. These mechanisms will be further explored in multiphase detonation systems, where droplet breakup, evaporation, and combustion interact with propagating detonation waves and influence detonation dynamics. These studies advance our understanding of shock-driven multiphase flows and provide a foundation for improved modeling of next-generation propulsion systems and hypersonic vehicle aerodynamics.