Experimental And Simulation Research On Cavitation Characteristics Of Staggered Double Hole Injector

As the main power unit of industrial machinery,diesel engine is widely used in the fields of diesel automobile,agricultural machinery and engineering machinery.With the development of industry,the energy demand of diesel engine is increasing,and the environmental pollution is becoming more and more serious.In recent years,the requirements of energy saving and emission regulations have become increasingly stringent,and the use of energy in China is developing towards carbon reduction and diversification.However,diesel engines will still occupy a high share in the power plant market in the foreseeable 20 years.Therefore,diesel engines still need to continuously improve their technical level to meet various needs.The nozzle is an important upstream boundary that affects the combustion of diesel engine mixture.The study of its cavitation flow characteristics is helpful to understand the spray atomization characteristics and the mixing rule of oil and gas.In recent years,the research on the cavitation flow characteristics of the injector mainly focuses on the single hole structure and symmetrical structure of the injector,but rarely on the staggered double hole structure of the injector.In order to further understand the influence of the nozzle structure on the internal flow characteristics of the nozzle,the cavitation internal flow of the staggered double hole structure nozzle was experimentally and simulated.The main contents are as follows:The visualization experiment platform of transparent injector based on high-speed camera was built to test the misaligned and non-displaced dual-hole structure fuel injectors respectively.It was found that the cavitation phenomenon of misaligned double hole structure nozzle was different from that of non-dislocated double hole injector.The experiment was carried out on the double hole injector with 45°inclination angle dislocation,and the complete injection process of the injector was photographed.It was found that the pressure in the injection nozzle decreases due to the fuel discharge in the injection nozzle in the setting stage of the needle valve.The cavitation amount produced by this reason was much greater than that in the lift stage of the needle valve.Experiments on different injection conditions were carried out with staggered double hole nozzle.It was found that under the same other conditions,as the injection pressure increases,the longer the stable injection of the injector lasts,the greater the maximum amount of cavitation in the injector;with the increase of injection quantity,the cavitation in the injector decreases.Experiments were carried out on two-hole injectors with different nozzle hole inclination angles,and it was found that the smaller the nozzle hole inclination angle,the earlier the cavitation occurred in the pressure chamber during the needle valve seating stage.And the nozzle with 45°inclination angle has a higher probability of linear cavitation in the initial stage of needle valve seating.Based on the Fluent software,the model which was consistent with the experimental nozzle was established,and the needle valve movement was realized by using the dynamic grid technology.The model was calculated,and the cavitation flow diagram inside the nozzle was compared with the experimental phenomenon,which verifies the reliability of the simulation calculation.It was found that in the seated stage of the needle valve,the swirl flow was formed in the pressure chamber by the nozzle with staggered orifice structure,which was conducive to the line cavitation;Through the analysis of cavitation volume curves in the nozzle and pressure chamber,it was found that the occurrence and collapse of cavitation in the nozzle are earlier than that in the pressure chamber.The factors affecting the cavitation flow of the misaligned dual-hole injector were simulated.By changing the dislocation spacing of the nozzle holes,it is found that the cavitation of the misaligned structure injector occurs earlier than the non-displaced structure injector.;With the increase of the dislocation distance of the nozzle holes,the vortex generated in the pressure chamber of the nozzle during the initial stage of the needle valve seating was more obvious,and the peak value of cavitation in the nozzle was also higher.By changing the nozzle inclination angle,it was found that during the seating phase of the needle valve,the cavitation rate of the nozzle pressure chamber with a small nozzle inclination angle was faster,and the peak cavitation volume was also higher.By changing the seat speed of the needle valve,it was found that the amount of cavitation in the injector increased with the increase of the seat speed of the needle valve.The faster the seat speed of the needle valve,the faster the occurrence and collapse of cavitation in the injector.In addition,the dimensionless number C_N that reflects the cavitation in the injector during the seating phase of the needle valve was derived,and theoretically explains the simulation phenomenon that the amount of cavitation in the injector increases with the increase in the seating speed of the needle valve.