THE EFFECT OF ACOUSTIC MODULATION ON SPRAY CHARACTERISTICS. I-Ping Chung, Hsu, University of California, Irvine, CA, USA. (NIST address: 221 / B312, (301)975-3899 (301)869-5924,

Combustion engines usually have poor partial load combustor performance primarily due to ineffective fuel atomization at low fuel flow rate. Poor atomization quality results in a lower evaporation rate and consequently poorer combustion performance. In order to maintain the atomization quality at partial load as same as that at full load in liquid injection systems, extra energy or perturbation is required. One proposed method is to provide perturbation in the liquid by an acoustically modulated device. The acoustic modulation is generated by a piezoelectric crystal driven by a high-frequency sinusoidal signal. The effects of acoustic modulation on liquid spray characteristics in a pressure swirl nozzle at partial load have been experimentally examined. The spray characteristics include discharge coefficient, spray appearance, spray cone angle, and spray patternation. An optical visualization technique is used to investigate the spray appearance and the spray cone angle. Spray patternation experiment is conducted with the liquid planar laser induced fluorescence (LPLIF) technique. The results show that the piezoelectric driver in the atomizer contains several discrete resonant frequencies. At these resonant frequencies, the acoustic modulation improves spray development and spray patternation, but has little effect on discharge coefficient and spray cone angle. The improvement is particularly prominent at a partial load injection pressure. Apparently, the acoustic modulation increases the perturbation of the liquid inside the nozzle and produces a condition for early disintegration of the liquid sheet issuing from the nozzle. Through this improved atomization, the acoustically modulated nozzle may improve the combustion process when engines are at partial load or idle condition.