Visualization Experimental Study On The Near-field Spray Characteristics In Diesel Engines

The fuel spray atomization quality of diesel engine has a huge influence on the combustion and emission characteristics,especially the primary breakup and atomization quality of in-cylinder spray,making the research on the diesel spray characteristics,especially on the near-field spray characteristics,meaningful.However,there are so many factors having great effects on the near-field spray,such as injection pressure,nozzle structure and fuel properties and so forth,besides,the spray in near-nozzle region scatters seriously and has the opacity characteristics,which makes it difficult to carry out the study on the near-field spray.Two different experimental test systems were used to investigate the near-field spray characteristics.The first is the ultra-high-speed shooting system to study the effects of the different orifice diameters,injection pressure and ambient pressure on the near-field spray cone angle and spray primary breakup characteristics.The second is the nanosecond flash shooting system to investigate the effects of fuel properties and injection pressure on the near-filed spray characteristics of diesel blending biodiesel,besides,the surface wave characteristics of near-field spray jet liquid core were also studied.The effects of different orifice diameters,injection pressure and ambient pressure on the near-field spray were investigated by using the ultra-high-speed shooting system.The results indicate that the profile of near-filed spray cone angle curve shows a three-phase development including the beginning-stage peak,the steady stage and the closing-stage peak.During the beginning stage,the beginning-stage peak would be larger under higher injection pressure or larger hole diameter,and the starting-injection performance would be better under higher injection pressure and increasing the hole diameter would deteriorate the starting-injection performance.Besides,the ambient pressure shows little influence on the near-field spray characteristics in this stage.During the closing stage,the closing-stage peak would be larger under higher injection pressure,or larger hole diameter,or higher ambient pressure,simultaneously,the closing-stage peak appear later and the duration of the whole injection process would be longer.During the steady-stage,the near-field spray cone angle would be larger with increasing the ambient pressure while the spray cone angle would be decreased under larger hole diameter.The effects of fuel properties and injection pressure on the near-filed spray characteristics of diesel blending biodiesel were studied through using the nanosecond flash shooting system.The results indicate that the morphology of the near-filed spray would be slender and the primary atomization quality would be poorer with the increase of the blending ratio.During the period from ASOI 0μs to ASOI 55μs,the spray penetration would be larger and shows a three-stage development while the near-field spray cone angle and the spray area would be decreased under larger blending ration.During the period from ASOI 55μs to the steady stage,the near-field spray morphology and the spray cone angle in steady stage under different blending ratio fuel both have the evident difference.When the injection pressure is low,the near-field spray shows the thin-stripes morphology.However,the spray begin to appear umbrella-like morphology as increasing the injection pressure.In early period of the beginning stage,near-field spray penetration,cone angle and the spray area would be larger under higher injection pressure.During steady stage,the he near-field spray morphology and the spray cone angle under different injection pressure also both have the evident distinctions.The wavelength of the near-field spray surface wave is mainly in the range of 13μm-100μm,presenting a cyclic variation(the wavelength increases firstly and then decreases).And the amplitude of the surface wave is increased as increasing the distance from the nozzle,mainly in the range of 4μm-52μm.There is no simple function relationship between wavelength and amplitude.At the same time,the increase of injection pressure has a positive effect on the surface wave,and the initial surface wave is closer to the nozzle.In this paper,some new research methods have been put forward to study the the near-field spray characteristics of diesel engine,and some achievements have been obtained.It has a certain reference value for the further study of near-field spray characteristics.