Pressure Dynamic Characteristics Of Diesel Common Rail System Simulation

Increasingly rigorous emission legislation and severe energy shortage force diesel to be developed for the objects of lower pollution, lower fuel consume and high power per weigh. However, the key to reduce emissions, improve diesel's power and fuel efficiency depends on improving diesel's combustion process, While improving the combustion process depends on well matching among the fuel injection system, the intake system and structure of combust chamber. Among these, the fuel injection system plays the most important role. And diesel engine high-pressure common rail electronic control injection system is the most effective in emission reduction and engine performance improvement among all of the fuel injection system currently. Since dynamic pressure characteristic especially pressure fluctuating inside rail directly refer to achievement of perfect injection rule, the study of rail pressure fluctuating have been one of current hotspots in high-pressure common rail system.The thesis established the flow model based on one-dimensional, unsteady, compressible, Navier-Stokes equations, and discrete the governing equations using a finite-volume formulation. Then founded the numerical models of fuel pump, rail and injector according to the structure of fuel injection system, and specified the numerical models as fluid model boundary. Above models were checked up by testing results, and the influence of different parameters in common rail system on dynamic pressure characteristic was simulated.Through the simulation, the main cause of pressure fluctuate was found, that is, injection pulse width and pump pulse width, the matching between two pulse width and time interval of the two pulse. The wider of the pulse, the larger of rail pressure fluctuate. Under the specified condition, the difference value of pressure fluctuate was up to 6-7Mpa. The select of rail volume and size was relatively effective measures. The most perfect rail volume value was between 30ml and 40ml, and the ratio value of length/diameter was between 40 and 80. The influence of spring and orifice diameter of outlet valve in pump mostly consisted in plunger volume, the infection of diameter of measure hole in injector control chamber on pressure fluctuate was not obvious, and the flow buffer component could give more attenuation of pressure amplitude.