Numerical simulations of a swirled turbulent spray flame: chemistry modeling effects on multi-regime combustion characteristics

Aeronautical gas turbine combustors feature turbulent spray flames, characterized by the complex interaction of atomization, evaporation, mixing, and combustion processes. The correct reproduction of these phenomena in numerical simulations is essential when investigating flames of unconventional fuels, whose peculiar physicochemical properties can impact the reliability and performance of combustion chambers. This work, based on the Cambridge spray burner n-heptane test case, aims to investigate the impact of combustion and chemistry modeling on the flame topology and characteristics. In the first place, the adequacy of the Flamelet Progress Variable approach in replicating multi-regime flames is assessed by comparison with finite-rate chemistry simulations. Results show that the tabulated chemistry approach fails to capture the extinction under high-strain conditions and overestimates the heat release associated with the same regime used to generate the laminar 1-D flamelet database. Additionally, the role of low-temperature chemistry (LTC) is evaluated by developing two skeletal mechanisms and analyzing the LTC contribution to the overall flame behavior. The low-temperature pathways are found to participate in the OH radical pool formation, thereby contributing to the stabilization of the outer lifted flame. Novelty and significance statement This study provides a comprehensive analysis of the impact of modeling on the combustion phenom- ena occurring in turbulent spray flames. Using the Cambridge lab-scale burner with n-heptane spray, the Flamelet Progress Variable (FPV) approach is compared against the finite-rate chemistry. In contrast to the FPV method, finite-rate allows for an accurate description of flame stabilization dynamics, extinction phenomena associated with turbulence-combustion interaction, and multi-regime combustion modes. Additionally, the role of low-temperature chemistry (LTC) in flame behavior is investigated through the development of two skeletal mechanisms, emphasizing the impact of LTC in the flame propagation assisted by the enhanced radical production. The key findings of this work strengthen the comprehension of modeling aspects related to the interplay between turbulence, chemistry, and the evaporation process in swirled spray flames, in view of the growing attention on the multi-regime combustion and lean blow-out sensitivity to the peculiar physicochemical properties of sustainable aviation fuels.