Informationofdropletsizeandsizedistributionlaysthebasisforinvestigationsofatomizationmechanismsandperformanceoptimization.However,thelaserdiffractionandphaseDopplerparticleanalyzershavedifficultyinaccuratelycharacterizingsprayswithawiderangeofdropletsizesandverylargedroplets,especiallyifalargenumberofdropletsareaspherical.Amethodtomeasuresizeinsuchlargedropletspraysbasedondigitalimagingwithbackwardilluminationwasdeveloped,includinganimageacquisitionsystemandimageprocessprograms.Calibrationofthemeasurementsystemwasperformedusingadotcalibrationtargetwithdifferentdotsizes.Anexperimentalsetupwasdesignedandestablishedtocharacterizespraynozzlesunderdifferentoperationloads,aswellasdifferentnozzlearrangements.Resultsshowthatthedropletsizeofspraysrangesfromdozensofmicronstoseveralmillimeters.Thesuperiorityofwideloadrangeforsuchnozzleswasindicatedbythesize-measurementresultsunderhalf-loadtofull-loadoperations.Thepresentstudyrevealedthattheimageprocessingtechniquecanbeeffectivelyimplementedforin-linesizemeasurementsofsprayswithawidedistributionofdropletsizeandasphericaldroplets,whichwouldbedifficulttocharacterizebyothermethods.
