Large eddy simulation of dual-fuel swirl flames

Dual-fuel combustion, where fuels of different reactivity are injected in the combustor separately in time or space, is important for some practical applications. This study employs Large Eddy Simulation (LES) coupled with the Doubly-Conditioned Moment Closure (DCMC) model to investigate dual-fuel flames, where liquid n-heptane (C7H16) is injected into a lean premixed methane/air (CH4/air) swirling stream. Two premixed equivalence ratios, ϕpmx=0.14 and 0.56, are studied, representing conditions below and above the lower flammability limit (LFL) of methane. Cold flow simulations and comparison with experimental velocity data suggest that the flow field is reasonably well predicted. Combustion simulations then explore the impact of ϕpmx on flame structure, with analysis performed in both physical space and conditional scalar space of DCMC. The results show good agreement with experimental observations in terms of flame shape and reaction zone location. The findings underscore the capability of LES-DCMC to capture key features of complex, multi-modal dual-fuel combustion systems.