The impact of nozzle shape on mixing, combustion efficiency, and flame blowout velocity.

Waste gas flares are subjected to a range of turbulent flow conditions that adversely affect combustion efficiency downstream of the nozzle. In extreme cases, this leads to flame extinction due to excessive straining, causing a rapid drop in combustion efficiency and a sharp increase in the concentration of vented waste gases. In this work, methane combustion in a jet in cross-flow is simulated for a range of momentum ratios and canonical nozzle shapes to understand the effect of nozzle geometry on mixing, combustion efficiency, and flame blowout velocity. The simulations are performed using large-eddy simulation (LES) coupled with a flamelet progress variable approach (FPVA). Blow-off velocity and mixing metrics are validated against a range of experiments. This study aims to understand the effect of the nozzle shapes, while holding the exit area constant, and identify the geometries that lead to better global mixing, provide better combustion efficiencies, and sustain flames at stronger crosswinds.