| In cylinder direct injection gasoline engine oil nozzle is an important component ofinjection system, With a great influence on the length and duration of injection, for thequality of fuel atomization spray and combustion chamber,combustion and emission Thespray quality is an important factor affecting the performance of GDI engine, goodatomization effects not only can enhance the power performance of GDI engine, but alsoreduce emissions, improve fuel economy. The fuel spray characteristics of nozzle internalflow and closely related, because the physical properties and increased fuel injectionpressure itself, internal flow of fuel injection nozzle is easy to produce cavitation; cavitation,a strengthening of the turbulent flow and atomization nozzle internal flow, but also reducesthe efficiency of the nozzle, and produce "cavitation" for the needle valve and needle valveseat, thereby affecting the nozzle life. Therefore, it is necessary to make deep research on thenozzle cavitation flow.Cavitation flow in high pressure swirl nozzle of GDI gasoline engine is a very complexflow phenomena in the nozzle, In a small area, it is difficult to get high fuel injectionpressure and fuel velocity, so the need for multi-dimensional numerical simulation of fuelflow is an effective research method with the aid of computer. Based on the high pressureswirl nozzle as the research object, using the method of computational fluid dynamics, usingthe Hypermesh to build3D mesh, simulate the transient cavitation flowin the GDI enginenozzle with the AVL-Fire software, numerical simulation, and the simulation results arecomparedFirst carries on the analysis to the cavitation flow pressure field and velocity field,pressure field of analysis that causes cavitation flow generated, analysis of the velocity fieldmeasured jet velocity and outlet fuel velocity. The formation and collapse of cavitation, the rules, in the needle valve movement of the early, cavitation in nozzle entrance around thecorner, along with the increase of the needle valve lift, the cavitation enhanced formation ofsuper cavitation, the pressure fluctuation at the super cavitation instability. The needlereaches the maximum lift, this time cavitation gradually weaker until it disappeared. Finally,began to decline, in close to the minimum lift near, between the needle and the needle seatring ring formed cavitation, cavitation does not spread to the nozzle exit,"cavitation" on thenozzle, is not conducive to the life of the nozzle. The needle movement in the process of thenozzle mass flow and outlet fuel velocity were studied, obtained the transient nozzle outletfuel mass flow and outlet velocity of outlet variation.In order to get the influence of injection conditions and nozzle structure on thecavitation flow, the different injection pressure, injection pressure, different nozzle diametersand different orifice length on cavitation, and the analysis of the conditions of the nozzle onthe fuel mass flow and outlet velocity, analysis results provide guidance for the design andGDI engine fuel injection mouth improvement, provide the boundary conditions for thesimulation of spray.For different injection pressure and injection pressure are simulated, found that thehigher the injection pressure, the cavitation number is higher,the cavitation is stronger,butthe time cavitation exists will get shorter. At the same time, analyzes the different spraynozzle export section pressure changes under transient fuel mass flow and fuel velocity. Thehigh pressure jet, cavitation number cavitation region is smaller, smaller, weaker cavitationcavitation, but some time longer, get the change regularity of different pressure transientnozzle export section of the fuel mass flow and fuel velocity... |
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