Experimental Study on Transient Ignition Characteristics of Acoustic Excited Methane Jet Diffusion Flames

Abstract

The ignition process of fuel plays an important role in the flame development and emission characteristics, which has attracted intensive attention in the combustion field. However, the transient ignition process for jet flames under acoustic excitation is rarely reported. In the current study, the effect of external acoustic excitation with different frequencies on the ignition process of methane jet diffusion flames has been studied experimentally using high-speed color and schlieren imaging systems. The fuel nozzle used in the experiment features a concentric ring structure, with fuel in the middle and air around it. The acoustic excitation was added to the air side through the loudspeaker, and the frequency of the acoustic excitation was set as 10 Hz, 30 Hz, 50 Hz and 100 Hz, respectively, while a case without external excitation was used as the control group. It is found that the periodic vortex structure propagates downstream in the flow field after acoustic excitation is added, which leads to an uneven velocity distribution in the flow field and the appearance of a local high-speed zone. The acoustic excitation of 30 Hz and 50 Hz can reduce the probability of successful ignition, which is mainly because the acoustic wave propagates in the flow field and causes drastic velocity changes near the ignition position. For the case of 100 Hz, the acoustic perturbation is confined in a small region near the nozzle exit, while the flow field velocity is slightly higher than the case without acoustic excitation.