Swirl-stabilized auto-igniting spray flames are essential for designing
efficient and clean combustion systems. The present study performs large eddy
simulations (LES) of the dilute auto-igniting methanol flame in a vitiated, hot
coflow of varying swirl intensities. The six-dimensional Flamelet Generated
Manifold (FGM) technique is used to solve the reactive flow accurately and
economically. The swirl numbers (SN), i.e. 0.2, 0.6, 1.0, E 1.4, are used to
assess their effect on auto-ignition and flame stability. At lower to moderate
swirl numbers (SN =0.2, 0.6), the increase in swirl is found to increase the
lift-off height. Beyond the critical swirl number (SN=0.6), the lift-off height
drops. Also, the time-averaged flame structure transitions from a tubular-like
flame into a uniformly distributed combustion region at these high swirl
numbers. It also results in a more compact flame for the higher swirl numbers.
These effects on flame dynamics are analyzed in detail using the mean gas-phase
flow field distribution, particle statistics, and proper orthogonal
decomposition (POD).

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