Effect of single and multiple acoustic frequencies on the atomization of a spray

A comprehensive investigation on the behavior of methanol and diesel sprays when subjected to single and multiple-frequency acoustic fields is provided. For all acoustic frequencies, the cone angle and penetration length rise while the Sauter mean diameter (SMD) reduces, indicating an atomization improvement in an acoustic field. Furthermore, the rise in cone angle/penetration length and decline in SMD are observed to be higher at lower frequencies, showing a significant enhancement in the atomization compared to the higher frequencies. Particle image velocimetry is employed to understand the spray dynamics in single/multiple frequency acoustic fields. The velocity vectors show a higher magnitude at lower frequencies compared to the higher ones, indicating the presence of higher acoustic streaming at lower frequencies. The presence of an acoustic source at the bottom of the sprays shows the formation of strong recirculation zones in the sprays, enhancing the mixing due to higher air entrainment because of intense streaming. The streaming is significant at lower frequencies compared to the higher ones. Furthermore, the data predicted using the Rosin-Rammler distribution model show good agreement with the measured one. Empirical relations are developed for the cone angle/penetration length/SMD. The smaller drops' number in the spray is determined to quantify the acoustic frequency's influence on the atomization. The presence of many smaller drops in acoustics is observed, and the number increases at lower and combined acoustic frequencies. Thus, the study unequivocally demonstrates that the presence of low/combined acoustic frequencies is essential for achieving an atomization enhancement.