Study On Spray Characteristics Coupled With Internal Nozzle Flow In High Pressure Common Rail Injector

The energy crisis in the world and the increasingly stringent emission regulations have put forward more and more requirements for the diesel engine's power,economy and emissions,and the spray characteristics and atomization effect of fuel are one of the important factors that directly affect the performance of diesel engines.The research shows that the atomization of fuel is influenced by some factors,such as cavitation,turbulence and aerodynamics.At present,the researchers have a clearer understanding of the aerodynamic factors,but the understanding of cavitation and other factors needs to be deepened.The high pressure common rail system improves the spray characteristics of the diesel engine effectively,but with the pressure increasing,the flow status in the nozzle is more complicated,especially the gas-liquid two-phase flow has an important influence on the atomization quality of the spray.It is of great significance for engineering practice to study the internal flow and the spray characteristics of coupled internal flow.In this paper,the research status of internal flow characteristics at home and abroad is reviewed from two aspects of experimental and numerical simulation,and the current situation at home and abroad of the spray characteristics coupled with internal flow is analyzed in detail.An accurate mathematical model for the internal flow is established.Based on the AVL FIRE simulation platform,the single-hole injector nozzle is numerically simulated using the linear cavitation model in the two-phase flow frame,and the motion grid is generated according to the needle lift curve.The fuel injection curve of the injection pulse width of 1.6ms under different pressures was measured through experiment.The flow discharge coefficient was calculated and compared with the simulation results to verify the correctness of the nozzle internal flow model.Based on the above model,the influences of the length-diameter ratio of the injection hole,the radius of the transition fillet,and the injection pressure and back pressure on the pressure distribution,velocity distribution,gas volume fraction distribution,and turbulent kinetic energy distribution were analyzed.A spray model of coupling nozzle internal flow characteristic is established,and the influence of the internal flow characteristics on the fuel atomization was analyzed.The parameters of the outlet section of the injection hole were used as the spray simulation boundary conditions,and the KH-RT spray secondary break-up model was used to simulate the spray.A high-speed camera was used to take a spray image at a pulse width of 1.6 ms.The image was binarized and the spray penetration distance was plotted against the injection time.The spray penetration distance curve and spray pattern of the test and simulation were compared to verify the correctness of the spray model that coupled theinternal flow characteristics.Based on the validated spray model,the effects of nozzle structure parameters and inlet boundary conditions on the macroscopic and microscopic properties of the spray were analyzed.