Research On Fluctuation Characteristics Of Cycle Fuel Injection Quantity For High Pressure Common Rail Fuel System

As a state-of-the-art injection technology,high-pressure common rail injection system(HPCRIS)has advantages including high injection pressure,adjustable injection timing and flexible injection rate.Fluctuation of cycle fuel injection quantity(FCFIQ)for HPCRIS influences the stability and reliability of diesel engines.Due to the mechanical,electronical and hydraulic multi-physics field coupled characteristic for HPCRIS,the interaction between parameters have significant effect on FCFIQ which decreases the coherence and percent of pass for the system.FCFIQ during multiple injection decreases the stability of control in economy,vibration and noise for diesel engine.For the diesel engine equipped with aftertreatment device,FCFIQ during multiple injection results in the instability of exhaust temperature,which decreases the transfer efficiency of the catalyst and leads to the exhaust coherence decline.Keeping the stability of cycle fuel injection quantity(CFIQ)and reducing the FCFIQ are the technical problems that needed to be improved.In this paper,a method of combining numerical modeling and experimental analysis has been adopted.Influence factors of FCFIQ,fluctuation characteristics of injector inlet pressure,FCFIQ characteristics of multiple injection for HPCRIS will be analyzed in depth.Then the CFIQ compensating strategy will be proposed.Finally,the nature rule and inherent property during fuel injection process will be revealed.The research results of this paper can provide technical support for the optimization design and the control of the FCFIQ of HPCRIS,and have important theoretical and practical significance for promoting the development of diesel engines electronic control injection system that has independent intellectual property.The following research works have been carried out in this dissertation.In order to reveal the influence factors of single injection FCFIQ,the interaction effects between the common rail injector parameters on FCFIQ will be analyzed.The multi-physics field coupled numerical model which including common rail,high pressure pipeline and electronic control injector,is developed and the state equations are derived.The experiments are conducted using D-optimal design method.A regression model of FCFIQ is proposed based on partial least-squares regression method.Verification and evaluation of the regression model indicate that the model has a goodness-of-fit and can predict the FCFIQ significantly.Through the significance analysis for the model terms at 95%confidence level,the influence factors that have significant effect on FCFIQ are obtained.The significant effects of the interactions between different parameters on FCFIQ are analyzed.In order to reduce the FCFIQ during multiple injection caused by the fluctuation of pressure wave in the system and propose the correction strategy of FCFIQ during multiple injection,the fluctuation characteristics of pressure wave are studied.The influence rules and mechanism of characteristic parameters on pressure fluctuation for injector inlet during single injection will be investigated.The fluctuation characteristics of CFIQ during multiple injection caused by the pressure fluctuation are investigated,including the fluctuation rules of main injection CFIQ and post injection CFIQ.The fluctuation mechanisms of CFIQ at two multiple injections are revealed.Through the investigation of damping hole on FCFIQ demonstrates that installing damping hole on common rail can decrease the fluctuation amplitude of pressure wave and reduce the subsequent FCFIQ for multiple injections.Based on the analogous theory between mechanical vibration system and hydraulic system,the pipeline will be equivalent to an undamped two degrees of freedom spring mass free vibration system which does to-and-fro beeline movement in horizontal smooth plane.The fluctuation frequencies of main injection quantity for pilot injection and main injection mode at different rail pressure are obtained.The relative damping coefficient,rail pressure,interval between pilot injection and main injection and pulse width of main injection are chosen as input variable,and the correction pulse width is chosen as output variable.Then the CFIQ compensating strategy will be proposed.Results show that the strategy has a good compensating efficiency that reduces the FCFIQ at multiple injections effectively.The maximum main fuel injection quantity fluctuation is decreased by 37.96%after correction.For purpose of revealing the nature rule during injection process further,the linearization of the system has been conducted.The state matrix of different typical working points during injection process at different injection mode and the variation rules of the rank for the state matrix at different intervals are obtained.The eigenvalue distributions of the state matrix during injection process in complex plane are analyzed making use of Lyapunov method.The variation rules of injection stability for the system are obtained.