Fluid Structure Interaction Analysis Of Acrylic Optically Transmissive Nozzles

Over the years,in order to convenient for experiment observing,experimental study on using optically transmissive nozzle to observe the inside flow of nozzle and near-field spray is developing.In the whole experimental setup,the optically transmissive nozzle is the key component to get high quality image,the test nozzle made by polymethyl methacrylate(PMMA)has been used in most of the visualization experiment currently.There are several reasons that the PMMA was chosen for the optical nozzle.Such as the higher light transmittance,higher mechanical strength,lighter weight and easier processing when compared with other organic material.The other reason is that the refractive index of PMMA is closer to the refractive index of diesel.The same refractive index can eliminate the influence of solid-liquid interface refraction on the imaging and expect to make the photograph more realistic.While during the visualization experiment,it was founded that the test nozzle was easy to produce cracks and cannot be used any more.On the basis of this phenomenon,in this paper,a three dimensional numerical simulation research was carried out for analyzing the solid deformation and stress distribution of the optically transmissive nozzle by using one-way Fluid-Structure-Interaction method.The simulation results show that the deformation and stress of the test nozzle are mainly concentrated in the sac and the entrance of the orifice.The maximum stress which not exceed the fracture strength of the material was observed at the entrance of the orifice.The cracks of test nozzle in the actual operation process always beginning at the solid plane where the sac entrance at.This is because the adhesive that injected to the plane was less when made test nozzle,which made the injector failed to fully bonded with that plane and the fuel would get into the crack between the injector and plane in the injection process.The fuel at the crack would caused high stress which over the adhesive force and cause the failure of the optically transmissive nozzle.Then the influence of different factors on the maximum stress was analyzed.The results show that the maximum stress increases linearly with the raise of injection pressure;while the stress value decreases when the nozzle diameter increased;the length of the orifice has little effect on the maximum stress;the higher fillet diameter at orifice entrance,the maximum stress is smaller;the oblique hole has less stress when compared with the straight hole.A interesting phenomenon was founded when made near-field spray visualization experiment: the fuel dripping phenomenon after the end of injection is obvious and the duration of the fuel dripping process is also longer than the actual injector when use the optically transmissive nozzle for experiment at the same injection pressure,it was maybe caused by the deformation of test nozzle.Then it was founded that there are also some differences about the fuel dripping phenomenon when the injection pressure and nozzle diameter were different.On the basis of contrast experiment results,the paper would research the effect between the deformation of test nozzle and fuel dripping phenomenon by using two-way Fluid-Structure-Interaction method.The results show that because of the solid expansion and contraction,the delayed time of fuel cut-off was longer than the actual nozzle and the total fuel mass discharging from the test nozzle was slightly increase.The simulation and experimental results were consistent.Then analyzed the differences about the fuel dripping phenomenon by changing the injection pressure,nozzle diameter and volume of sac.The results show that the injection pressure has a indirect effects on fuel dripping phenomenon by influencing the deformation of the test nozzle and the higher injection pressure,the phenomenon is more obvious;differences of nozzle diameter has little effect on the fuel dripping phenomenon;the larger sac volume make the expansion and contraction of solid become more obvious and resulting in duration of the fuel dripping phenomenon is longer.