Development And Validation Of Unit Pump Injection System Computation Model

Combustion process is the key factor to affect the performance.The injection characteristics of the injection system are the main influence factors to improve the combustion characteristic of the engine.There are two methods to improve the injection characteristics: theoretical study of injection mechanism and experimental research.At present commercial software can basically meet the needs of injection macro characteristics.But it’s difficult to improve and research characteristic based on theoretical model.In order to study the injection mechanism,it’s necessary to develop theoretical model.Therefore,theoretical research of each stages of injection process is particularly important.Building own mathematical model on the basis of theory study,then through the programming to complete its numerical calculation,and ensure model accuracy and reliability by experimental verification,the resulting simulation model can provide guidance for improving and enhancing the injection characteristics of the engine fuel injection system.So the economical and emission characteristics can be improved by the optimization of the combustion process.The main research object of this paper is unit pump fuel injection system.Firstly,unit pump injection experimental system and its working principle was introduced in this paper.In order to verify the accuracy of simulation results.Cycle fuel injection volumes experiments of different temperatures and different backpressures and pump pressure experiments of different speeds and different injection pulse widths were completed on unit pump fuel injection test platform.Analyses of test data and error were also introduced and calculated.Secondly,based on the unit pump injection system’s physical model and basic working principle,according to the geometry structure of injection system and the dynamic law of pressure propagation,taking into account the fuel compression coefficient and fuel density changed with pressure.Mathematical model of cam,wheel,high-pressure oil supply pump,one-dimensional unstable flow of fuel in high-pressure pipe and mechanical injector were built.Choosing the high-pressure tubing to divide the calculation unit.In its characteristic line,then transformed the solution of partial differential equations of the fuel flow in high-pressure pipe into the solution of ordinary differential equations in its characteristic line.Each boundary equations,node equations of high-pressure pipe were combined to solve the fuel status parameters of every moment and point,the calculation formulas of the important parameters in injection simulation calculation process were also provided.With the mathematic model simulation program,pressure waveform of the injection system and cycle fuel injection volumes were obtained.At last,comparing the simulation results with the experimental results,it shows that the error between simulation results and experimental results was within the acceptable range,therefore,the simulation model in this paper has certain credibility.Through the results of simulation and experiments,it was obtained that,cycle fuel injection volumes decreases with increasing backpressure at the same temperature;and it also decreases with increasing temperature at the same backpressure.The analysis of the relative difference between cycle fuel injection and peak pressure showed that,at the same speed,as the injection pulse width increases,the relative difference of peak pressure decreases gradually;at the same injection pulse width,the relative difference of peak pressure at 900r/min was greater than that of 1200r/min.