Investigation On Dynamic Characteristics Of Diesel High Pressure Common Rail Fuel Injection System

Development trends in high pressure common rail(HPCR)fuel injection system reflect state-of-the-art electronic fuel injection system which has excellent ability in improving the performance of diesel engines through flexible control of injection pressure and injected fuel quantity.Dynamic characteristics of fuel supply and injection can directly influence the HPCR system's performance.Therefore further investigations in fuel supply performance of high pressure pump and stability of cycle fuel injection quantity(CFIQ)are the two technical problems which needed to be improved.In this thesis test benches for electromagnet force testing,fuel supply performance of high pressure pump and injection performance of HPCR system will be established.A numerical model for electromagnet force will be developed in Maxwell Ansoft and redicted magnetic force will be mapped in AMESim numerical model of HPRC system.HPCR AMESim model couples various fields including electric,magnetic,mechanical movement and flow using co-simulation method.Predicted accuracies of both numerical models will be verified through comparisons with experimental results.Based on these validated numerical models HPRC fuel injection dynamic characteristics and fuel supply performance will be thoroughly investigated.Moreover,a novel electronic fuel injector for HPCR system will also be proposed.Firstly,main influential parameters of high pressure pump and their influence laws on fuel supply quantity are studied.Fuel supply dynamic characteristics of high pressure pump would be obtained by analyzing the regulation characteristics of volume control valve(VCV)and velocity characteristics of cycle fuel supply quantity.Frequency coupling characteristics of fuel supply will be studied using frequency domain analysis method.Then the influence of frequency coupling effect between VCV and fuel supply plunger on fluctuation characteristics of VCV outlet flow rate and the influence of VCV operating frequency on fuel supply characteristics are going to be revealed.Main influential parameters of key components and their influence law on cycle fuel supply quantity will also be presented after detailed investigations.Secondly,main influential parameters of HPCR system and their influence laws on cycle fuel injection quantity(CFIQ)are studied in detail.These influence laws along with generation mechanism of cycle fuel injection quantity fluctuation(CFIQF)caused by variations of different parameters should be analyzed thoroughly.Quantitative analysis method is refined by using the proposed definition of relative CFIQF.Percentages of CFIQF shall be computed through quantitative analysis and critical influential parameters of HPCR system will be obtained.Then the correlation analysis will be carried out on CFIQ.Variation of correlation coefficients as a function of CFIQ for both first-order factors of all individual influential parameters and second-order factors with considering interaction between all individual influential parameters will be analyzed.Injection characteristics of small fuel injection quantities will also be analyzed.Reasons for inflection points in CFIQ curves and the influence law of key influential parameters for small fuel injection quantities will be presented in detail.Thirdly,fluctuation characteristics of CFIQ in pilot-main injection and main-post injection are investigated in order to further clarify CFIQF characteristics of HPCR system in multiple injection processes.The main reason why there is CFIQF in multiple injection processes should be revealed.Then pressure fluctuation characteristics will be analyzed and an LC undamped hydraulic mathematic model is going to be developed for predicting fluctuation cycle and frequency of pressure wave.On the basis of this a pressure wave prediction equation should be proposed for predicting the pressure fluctuations of both single and multiple injection processes.Finally,a new type of electronic injector with dual sealing surface control valve is going to be proposed for reducing the impact of variations in parameters of injector on CFIQ,cutting down the correlation between interaction of influential parameters and CFIQ and decreasing the cycle fuel return quantity of injector and reducing CFIQF in multiple injections by accelerating the decay rate of pressure fluctuation amplitude caused by fuel injection.And Injection characteristics of novel electronic injector will be simulated and studied through developed numerical model in AMESim.