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, i-ping.chung@nist.gov
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.