Effect Of Fluid Properties And Piezoelectric Transducer Modulation On Liquid Sheet Disintegration Of A Simplex Pressure-Swirl Atomizer.

I-Ping Chung and Cary Presser

National Institute of Standards and Technology, Chemical Science and Technology Laboratory, Process Measurements Division, Gaithersburg, MD 20899, USA

Combustion of liquid fuels in diesel engines, spark ignition engines, gas turbines, rocket engines, incinerators, and industrial furnaces strongly depends on effective atomization. Many factors can affect the performance of atomization, but for any given type of atomizer, operating pressure and fluid physical properties (i.e., viscosity, surface tension, and density) are the major parameters. This study investigates the effect of these fluid properties on the atomization process, and in particular, on liquid sheet disintegration of a simplex pressure-swirl spray. A piezoelectric transducer atomizer is used to improve liquid sheet disintegration and the effect of modulation is also examined. A stroboscope photographic technique is used to visualize the disintegration process of conical liquid sheet. Eight different fluids are used, in which viscosity varies from 0.9 to 6.0 mm2/s, surface tension changes from 0.023 to 0.072 kg/s2, and the variation in density is small. The experimental results indicate that fluid properties influence both the discharge coefficient and liquid sheet breakup length. The piezoelectric transducer atomizer contains several discrete resonant frequencies. At these resonant frequencies, the piezoelectric transducer modulation has little effect on discharge coefficient but shortens the breakup length. This effect is attributed to waves imposed along the liquid sheet surface that amplify wave-mode and rim-mode disintegration and assist in liquid sheet breakup. The wavelength generated by the modulation is found to depend on the driving frequency and fluid density. The resonant driving frequency is affected slightly by the fluid density. For our experimental arrangement, an optimum driving frequency, for which the liquid breakup length is a minimum, is found to occur at about 10 kHz. A higher input modulation power enhances disintegration. The relationship between the breakup length and the modulation power is in a cosh-1 function.