Effects of jet pulsation intensity on a wake-stabilized non-premixed jet flame in crossflow

• Jet pulsation intensity changed flow modes and therefore changed flame behaviors.
• Enlarged vortices, irregular puffs, up-down oscillating bent jet were developed.
• Shear-layer vortices and recirculation bubble dominated flame behaviors.
• Excitation significantly improved mixing.
• Excitation significantly reduced combustion-induced pollutants.

The jet pulsation intensity effects induced by acoustic excitation on a non-premixed fuel jet flame in crossflow were experimentally studied in a wind tunnel at the crossflow Reynolds number Rew = 1416, jet Reynolds number Rej = 1550, jet-to-crossflow momentum flux ratio R = 0.192, and excitation Strouhal number Stexc = 0.21. The jet pulsation intensity Ipul varied from 0 to 0.9. The flame behaviors, stability mechanism of flame blowoff, flow patterns, and thermochemical fields were measured and discussed. The time-averaged and instantaneous flame appearances were photographed by a high speed camera. The instantaneous flow patterns were obtained by the laser-light-sheet-assisted particle-tracing method. The temperature and concentrations of combustion-induced pollutants (unburned HC, CO, and NO) were measured by a fine-wire R-type thermocouple and a gas analyzer, respectively. Analysis of the measured results showed that the flame and flow behaved differently within four ranges of jet pulsation intensities (slight, medium, strong, and over excitations). The flows presented different characteristic modes of enlarged shear-layer vortices, irregular puffs, up-down oscillating bent jet in different ranges of jet pulsation intensities, and therefore induced different flame behaviors in different ranges of jet pulsation intensities. The primary flow features leading to modifications of the flame behaviors were the upwind shear-layer vortices and the recirculation area around the leeward side of burner tube tip. Appling excitation to the combusting jet in crossflow at Ipul > 0.55 could lead to significant improvement in mixing and combustion and reduction of combustion-induced pollutants.