| Fuel is the major working media during the operation of the diesel engine in cylinder. Jet flow is closely related with the diesel engine power, economy and emission performance. Meanwhile, the jet flow behavior is very complicated under the practical operation of the diesel engine, which includes fuel broken, atomization, evaporation, mixing and others'physical and chemical process. A deep knowledge of these behaviors is helpful for us to understand the working process in cylinder and the reduction of harmful emissions. The mechanism and influencing factors of fuel atomization is deeply analyzed in this paper. And the application potential of the injection control condition and injector structure and layout are investigated in order to improve fuel jet behavior and optimize combustion process.In order to deeply understand the principle of the breakup and atomization of fuel jet in cylinder, the research results of others were analyzed and summarized, the flow behavior inside the orifice was deeply and roundly studied in this paper. The flow inside the orifice was subdivided into single-phase flow, partly cavitation flow, fully cavitation flow and plug flow. The four different flow regimes correspond to different gas/liquid two-phase flow distribution and structure, and had influences on the atomization process of jet out of the hole. For the further understanding of detail features about the flow process inside the orifice during the injecting process, single hole nozzle was numerically studied by dual fluid model in FIRE software. With the needle valve lift and fuel injection time changed, the flow state inside the hole changes apparently from single-phase flow gradually evolved into cavitation flow and the flow structure appears bi-region distribution gradually. Toward the axisymmetric nozzle, in the center of nozzle there is a higher density, higher velocity and weaker turbulence liquid area, and near the orifice wall there is a less density, lower velocity void area with more air bubble. When it comes to asymmetric orifice, the distribution of cavity bubble and flow parameter present asymmetric distribution, the void area exists around the upper wall. At the same time, based on a real injector with seven holes, the injection pressure, the backpressure, fuel characteristics and inlet rounded corner diameter ratio R/D, length rate L/D, inlet /outlet aperture ratio K and other structural geometries was studied .The results showed that these factors made high impact on the flow characteristics. The proper choice of these factors can enhance the cavity, turbulence and velocity of the inducing jet-flow that improves the atomization.Based on the study of the various atomization hypothesis and models, combining with the characteristics of FIRE software and the study of flow characteristics inside the hole, a more accurate and detailed description of the jet flow atomization procedure was put forward. In the model, turbulence, cavitation and aerodynamic were all important factors on the effect of jet flow atomization procedure. Cavitation and turbulence in the nozzle are one of the dominant factors to induce jet flow primary atomization. Turbulent kinetic energy and cavitation bubble motion in the nozzle greatly strengthen initial perturbations on the jet surface. Then the initial disturbance surface wave further developed under the influence of aerodynamic and finally broken isolated droplets. In the process of establishing the model, spray atomization processes was divided into primary breakup and secondary breakup to be simulated. Primary breakup near the nozzle hole, the flowing characteristics of nozzle and spray model contacted by additional grid and the basic measure of liquid can be calculated by Conservation of Mass. Then broken droplet was accordingly released in liquid core surface mesh. The length and diameter of droplets were obtained by length of turbulent in this model. The impact of the bubble cavity was treated as a source of turbulent phase equation. Atomization time scale is the weighted average of turbulence and aerodynamic crushing.The accurate condition of original injection was given to this model. SMD and spray cone angle can be calculated by this model. At the same time, KH-RT model was used to simulate the droplet atomization process of secondary breakup. The unstable breakup models of KH and RT were coupled in this model which applied to many breakup models of low and high Weber number.Based on the non-axisymmetric and axisymmetric structure, the effect Liquid-Gas Distribution on the process of jet puverization was studied. The results showed that the jet flow of the axisymmetric nozzle is axisymmetrical distribution and the non-axisymmetric nozzle jet flow was non-axisymmetric. The reason is that the bubble of cavity is non-uniformity distribution in the hole of the non-axisymmetric nozzle. The disturbance to jet flow was strengthened in the thicker side of the cavity area after the cavity collapsed. The body of the jet disturbance was significantly enhanced speed jets and fragmentation solution greater radial kinetic energy drops, which have large diffusion cone angle, while the hole on one side of the bubble is less contrast.Utilizing atomization model and the structure of jet atomization in the visual experiment, the influence of different injection conditions and spray hole structure on the jet atomization of porous nozzle holes were further studied. The results showed that the jet structure, spray penetration and cone angle were more consistent with the experimental results by the detailed coupled original boundary. Reasonable injection conditions and improved jet nozzle structure can effectively change the nozzle exit flow state. The jet atomization is improved , which expand the geographic distribution of droplets and promote fuel and gas mixture. Therefore the optimization on the two aspects of the spray conditions and the nozzle structure is important technical means to improve the diesel combustion process and reduce harmful emissions.In order to further understand the combustion process and the jet flow behavior in the complicated surroundings in cylinder, the research platform of the in-cylinder working process of the numerical simulation and experiment was established based on the YD4A75-C3 diesel engine. To deeply and quantificationally analyze the fuel distribution characteristics, combustion and the generation process of harmful emissions NO and Soot, the paper introduced the microscopic information quantity analysis method. The results showed that rate of heat release of prophase and intermediate combustion was higher. Because much fuel burned and heat rejection is much, the temperature is high at the area of high exothermic rate in this stage. The distribution of fuel is concentrated totally and the fuel spread inadequately, so the utilization of air is low at the process of combustion. The combustion is diffusive combustion. The heat was mainly absorbed by unburned fuel and combustion products which was the main factor of creating high temperature at some places and harmful emissions.Combined with the high-pressure common rail system of high degree of flexibility the injection pressure, main injection timing, pre-injection and post injection were studied in this paper based on the close relationships of jet flow, combustion process, high temperature zone and pollutant generation. The factors of nozzle hole number, diameter of nozzle hole, arrangement of nozzle hole and post injection were also studied. The research results showed that the jet flow, the diffusion motion of fuel, the distribution areas of fuel and the utilization of air was improved better and the harmful emissions was reduced when the injection condition and nozzle structure were reasonably improved.
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