Swirl effects on global and chemical behavior of flames

Flame characteristics are reported for four lean direct injection (LDI) method flames using direct flame photography and optical emission spectroscopy (OES). The flames included three counter-swirl and one coswirl configuration using a double concentric swirl burner. The chemiluminescent images for the OES technique are acquired using an intensified charge coupled device (ICCD) camera and narrow bandpass filters centered at wavelengths sensitive to the specific specie of interest. The swirl imparted to the combustion air in outer annulus of the burner is kept constant (swirl vane angle 50°) with direction varied in one case while the swirl vane angle to the inner annulus was varied as 30, 45 and 65 degrees, respectively. This swirl number variation provides observation of low, medium, and high swirl strength. The direct flame photographs show that mixture mixedness increases with swirl strength and results in decrease of flame length. Spatial distribution of the flame species OH, CH, and C₂ provided an insight on the chemical behavior of flames. The reaction zone, marked by the OH intermediate species, increases in intensity with the increase in swirl strength. These features are corroborated with the global flame photographs.