Study of auto-igniting spray flame in vitiated swirling hot coflow using flamelet generated model

Swirl-stabilized auto-igniting spray flames are essential for designing efficient and clean combustion systems. The present study performs large eddy simulations of the dilute auto-igniting methanol flame in a vitiated, hot coflow of varying swirl intensities. The six-dimensional Flamelet Generated Manifold technique is used to solve the reactive flow accurately and economically. The swirl numbers (SN), i.e., 0.2, 0.6, 1.0, and 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 liftoff height. Beyond the critical swirl number (SN = 0.6), the liftoff 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.