喷雾中液滴粒径，浓度，温度分布基于SLIPI方法的测量

Structured laser illumination planar imaging (SLIPI) is a technique capable of
suppressing multiple light scattering effects in optically dense sprays, resulting in
spray images without blurs and with enhanced contrast. The novelty of the work
presented in this thesis concerns the applications of a variety of SLIPI-based
techniques for the measurement of droplet size, droplet concentration, and liquid
temperature in atomizing sprays. Two types of spray systems are investigated
here: 1) Steady hollow-cone water sprays using temporally averaged imaging.
2) Transient Direct-Injection spark ignition (DISI) biofuel sprays using
instantaneous imaging.
The temporally averaged measurements are performed using three-phase SLIPI
(3p-SLIPI) with liquid injection pressures in the range of 20–50 bar and at ambient
conditions. Droplet sizing is obtained by combining SLIPI with the laser-induced
fluorescence (LIF)/Mie ratio approach, where the droplet Sauter mean diameter is
deduced after calibration with phase Doppler anemometry measurements. The
droplet concentration and liquid volume fraction are obtained by combining the
SLIPI-LIF/Mie method with light transmission measurements. This is performed
using a laser sheet scanning approach, which provides three-dimensional
quantitative reconstructions. Finally, the spray temperature is obtained by
combining SLIPI with two-color LIF ratio thermometry for a liquid temperature
ranging from 25–55°C. It is found that multiple light scattering induces
measurement errors even for sprays having singly scattered photons in majority.
This finding, therefore, strongly supports the application of SLIPI for quantitative
spray measurements, even for optically dilute sprays. The 3p-SLIPI approach is
based on recording a minimum of three modulated sub-images successively, each
having a different spatial phase; therefore, it has been primarily used for
temporally averaged imaging.
To circumvent this limitation, two novel instantaneous imaging approaches, 2p-
SLIPI and 1p-SLIPI (corresponding to two-phase and one-phase, respectively),
have been developed. In the 2p-SLIPI optical setup, the “lines structure” is
optically shifted by exploiting the birefringence property of a calcite crystal. This
novel optical approach is used to image spray dynamics in ethanol and butanol
DISI sprays at liquid fuel injection pressures of 80 and 160 bar, where the spray
chamber is operated at 2-bar air pressure. Finally, the results from instantaneous
2p-SLIPI and 1p-SLIPI imaging have been compared, showing promising
applications for the study of spray dynamics.