Research On Multi-physical Field Coupling And Multi-parameters Step-by-Step Optimization Of GDI Injector

Compared with the traditional PFI gasoline engine,the Gasoline Direct Injection(GDI)engine has more prominent advantages in energy-saving and emission reduction.The domestic and foreign researches show that the GDI technology will become the main trend of automotive gasoline engine in the future.The GDI injector is a key componentin combustion engine which impact mixture forming quality and emissions of the combustion engine.Therefore,to meet higher requirements of vehicles on economics and ever-stringent exhaust emission regulations,improving the GDI injector performance becoming a hot topic in the field of fuel injection.The working process of GDI injector is affected by its structure,electromagnetic field,temperature,flow field,etc.,and those physical fields have multiple interactions and complex coupling relationships,which makes improving the GDI injector performance become a difficult problem in the field of fuel injection.This research is focus on the coupling mechanism and the structure parameter optimization methods of GDI multi-hole injector.The coupling forms and transitive relation are analyzed based on the subsystem models of GDI multi-hole injector.The different parameters impact on the electromagnetic and spray performance are analyzed by multi-physical coupling simulation,and the magnetic circuit and the nozzle structure are optimized by multi-objective optimization step by step.At last,the comperhensive performance prediction and the overall structure optimization of GDI injector is achieved by this method.The main researches of this paper include the following aspects:Based on the foreign typical GDI injector structures,a multi-hole GDI injector structural is established by surveying and mapping.According to the basic principles of electromagnetism,mechanical dynamics,fluid dynamics and thermodynamics,the subsystem models including the electric circuit,magnetic circuit,mechanical movement,electromagnetic loss,flow and fuel spray are established.The coupling characteristic and transmission relations of the multi-physcial parameters among the multi-physical fields are analyzed,which lays a foundation for the multi-physical field coupling analysis and multiple objective parameter optimizations.The multi-physical fields coupled forms and their solving methods are analyzed systematically.The convergence,distribution and operation efficiency among four kinds of multiple objective intelligence-optimized algorithm are evaluated by using the knapsack problem.Finally,multi-objective simulated annealing(MOSA)algorithm is determined to solve the magnetic circuit structure optimization.According to the coupling character of multi-physical parameters of GDI multi-hole injector and the finite element theory,data interfaces which can link the Simplore,Ansoft Maxwell,Thermal,Fluent and other simulation softwares are established based on the primary platform on ANSYS Workbench and data interactions among the parameters of multi-physical fields are achieved.By using the finite element method,the electric-magnetic-thermal coupling process of GDI injector is analyzed.Thevariation laws of current,magnetic induction intensity,temperature and dynamic response performance and the influence from the change of body temperature on its dynamic response performance are analyzed in detail.With the temperature rising of the GDI injector body as sources of heat and the inner heat transfer property is analyzed.Based on the boundary condition of the thermal-fluid coupling,the time step iteration method is used to simulate the process of the thermal-fluid coupling of the GDI injector.The effect of flow conditions on the temperature rising of the GDI injector and the temperature rising of the GDI injector effect on the flow conditions and spray characteristic are analyzed.At last,both of the viability and validity of the multi-physical field simulation method are verified from different aspects,including the dynamic response performance,temperature distribution characteristic,inner flow and spray characteristic through experience.Becasuse coupling characteristics of magnetic circuit parameters andnozzle structure parameters are indirectly and weak,soa step-by-step optimization strategy is designed tooptimize the magnetic circuit parameters and nozzle structure parameters.When optimizing the magnetic circuit structure parameters,the MOSA algorithm is used to improve the dynamic response and structure compactness properties and reduce energy consumption.The results show that,after magnetic circuit structure optimization,the structure size of the GDI injector is lessen,electromagnetic loss is decreased and the dynamic response characteristic is improved.According to the design principle of nozzle,the orthogonal experiment method is used to optimize the nozzle structure parameters based on magnetic circuit structure completed.By using the principles of statistics,the nozzle structure impacts on the internal flow and external spray performance is revealed.The results show that,after nozzle structure optimization,spray particle diameter decreases obviously and the spray pattern and penetration basically unchanged.Finally,the manufacturing techniques of the GDI injector are studied thoroughly and the materials selection,technological design and the assembly plan are done.A batch of injector samples are trial-produced based on the original and optimized GDI injector structures.The variation of the temperature,dynamic response performance,spray characteristic and flow rate ofthe original or optimized injectors are tested by comprehensive performance tester of GDI injector.Experimental data indicate that the comprehensive performances of the optimized GDI injector are improved significantly,at the time the method in this dissertation can provide a reliable theory to the prediction and evaluation thecomprehensive performances of GDI injector and can guide its structural optimization.