Computational study on the effect of thermodynamic operating conditions on primary atomization in pressure-swirl atomizers

• DNS-like simulations were done to study atomization in pressure-swirl nozzles. • Two thermodynamically different injection conditions were modelled and compared. • An earlier breakup was observed to happen when injecting fuel at higher temperature. • The high-temperature condition presented a better atomization efficiency. • Both cases showed a droplet-size growing trend when going far from the nozzle. Reducing pollutants and carbon emissions is a main and commonplace concern nowadays. Improving liquid breakup efficiency in injection processes for combustion applications may lead to important benefits in that regard. In this work, the effect of varying the injection conditions in terms of their thermodynamic state is studied when injecting liquid fuel into quiescent air through a simplex pressure-swirl atomizer. For that purpose, high-fidelity DNS-like simulations are carried out. Results, validated by comparing the spray macroscopic shape with experimental pictures, show a realistic breakup mechanism already observed in previous studies. An improvement in breakup capabilities is observed when preheating both fuel and air. In this case, the injected liquid sheet is thinner and presents more instabilities, leading to an earlier breakup in the axial direction. Besides, the generated droplet population is larger and finer than that of the ambient temperature injection, indicating a better atomization efficiency. A size-growing trend is observed in the droplet population for both cases when getting far away from the nozzle, but is more noticeable in the low-temperature condition. This investigation helps to understand the first stage of the liquid breakup in pressure-swirl atomizers. Its results, complemented with those from simulating different operating conditions or fuels for the same atomizer, can be used to elaborate prediction models able to faithfully represent the primary atomization outcomes when using lower resolution methods more accessible from the computational standpoint. Besides, the importance of internal injector flow characteristics is also demonstrated, particularly when considering liquid film thickness, both mean and fluctuation. These findings indicate that a possible model based on internal injector flow studies may also be feasible for determining atomization efficiency.