On-line testing of fuel injector flow coefficient based on 3D modeling
[Objective]To improve the efficiency and fuel economy of diesel engines,researchers have focused on online measurement and accurate control of key actuators.Among these actuators,the injector has emerged as a vital component of the fuel system.The injection characteristics of the injector directly influence the combustion process and emissions from the engine cylinder.The discharge coefficient of the injector nozzle is a crucial parameter that significantly affects fuel consumption,smoke emissions,and external characteristics of diesel engines.[Methods]This paper introduces an innovative one-dimensional mathematical model applied to the online measurement of the transient discharge coefficient of diesel injector nozzles.Changes in the fuel system are represented by the transfer and evolution process of the Riemann wave.A direct mathematical relationship between pressure and the transient discharge coefficient within a single Riemann wave environment is established.Moreover,this paper introduces a method for recognizing the time-domain characteristics of the input signal and segmenting the model based on these time characteristics to improve its performance.The analysis of injector characteristics and pressure signals indicates that changes in the fuel system state can be represented by the transmission and evolution process of the Riemann wave.According to the one-dimensional unsteady flow theory,the Riemann wave is described in terms of fuel pressure(dP)and flow velocity(du).Furthermore,this paper establishes a direct mathematical relationship between the pressure signal and the discharge coefficient.Upon analyzing the actual fuel system structure,a decoupling algorithm for the reflected wave W3 and a correction method for interference wave W1 are introduced.[Results]The results indicate that this method effectively eliminates pressure wave components caused by noninjection processes,thereby significantly improving the accuracy and applicability of the model.The decoupling algorithm of the reflected wave and the correction method of the interference wave are introduced to improve model performance.Experimental results confirm the high accuracy of the mathematical model.The nonlinear variation of the average discharge coefficient with injection pressure and pulse width can be attributed to cavitation and the average opening of needle valves.The use of measurable physical signals in the actual working process of the engine as input enables the real-time demands of the engine control system to be met through reasonable hypotheses and advanced algorithms embedded within the model.[Conclusions and Prospects]This paper presents an innovative one-dimensional mathematical model for the transient discharge coefficient.Using the pressure at the injector inlet as input,an algorithm for determining the transient discharge coefficient is introduced.This model can be used for fault diagnosis,injector health evaluation,and controlling the injection mass under various working conditions.Experimental verification confirms the accuracy of the calculated results.The goodness of fit between the calculated and measured values exceeds 0.93.Analysis of the average discharge coefficient reveals a nonlinear relationship with the injection pressure and pulse width owing to the influence of average nozzle opening and cavitation.
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