Liquid Fuel Atomization and Evaporation in Complex Geometries Using High-Fidelity Multi-Scale Simulation Methods

Modern combustion systems used in applications like automotive, ship and aerospace engines are increasingly focused on advanced technologies that may enable to reduce pollutant emissions and incorporate carbon neutral fuels. In such systems mainly fired with liquid fuel, the process of liquid injection is essentially realized under non-isothermal conditions making the whole liquid injection a very complex phenomenon featuring a wide range of length and time scales. Thereby, complex interaction processes take especially place between flow dynamics, atomization, evaporation, turbulent mixing and combustion, which critically influence fuel-air mixture formation and pollutant generation. Understanding these processes is vital not only for advancing nozzle design, but also for optimizing fuel-air mixing, and improving combustion efficiency. High fidelity numerical simulation techniques are able to support such a challenge. That is why, in the present work, a novel multiscale approach is developed which saves computational costs and is able to capture correctly the whole spray formation and dispersion while including the in-nozzle flow, the liquid fuel atomization and the phase change throughout the spray regions. The suggested approach consists in a seamless coupling of the Volume of Fluid (VOF) method and the Lagrangian Particle Tracking (LPT) within a high-fidelity framework based on Large Eddy Simulation (LES) techniques. Adaptive Mesh Refinement (AMR) is incorporated into the simulation setting to dynamically enhance the resolution of the liquid-gas interface, effectively lowering computational costs while ensuring accuracy. The coupling algorithm is implemented into the open source CFD code OpenFOAM. First, the model is developed and validated to deal with isothermal applications of liquid jet injection, and then applied to three practical configurations, namely the liquid jet injection in cross-flow (LJICF), the spray atomization from a pressure swirl atomizer, and the spray atomization with co-flow effects from a spray burner. The results successfully reproduce the key atomization processes, including the in-nozzle flow, the jet penetration, the breakup and the droplet dispersion, while highlighting the significant influence of turbulent co-flow on the spray cone angle, sheet thickness, breakup length and droplet distribution. Encouraged by these impressive achievements, the approach could be then extended by consistently integrating the phase change into the overall modeling. This makes it possible to investigate practical configurations under non-isothermal conditions. Two cases are selected for this purpose. The first allows to analyze and quantify the influence of evaporation on the entire spray evolution in LJICF. The second brings to the fore the effects of different crossflow temperatures on atomization, evaporation, spray dispersion, interaction between turbulence and evaporation, as well as on turbulent mixing in LJICF. Overall, the extended methodology effectively captures the influence of phase change on spray dynamics in the near-nozzle region, including instabilities, breakup through appropriate breakup diagram, and penetration length of the liquid jet. In addition, it allows to quantify the influence of crossflow temperature on evaporation rates, droplet sizes, turbulence-evaporation interaction thanks to a targeted evaporation Damköhler number, and turbulent mixing through specific selected measures in the dilute spray region far from the nozzle. Comparisons with experimentally available data demonstrate the predictive accuracy and reliability of the developed approaches. In summary, these accomplishments ensure significant progress both in the development of the methodology and in the analysis of the phenomena. The established method provides a solid basis for future extensions, including combustion and other complex processes.