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.