| Since 21 Century, the energy crisis has become increasingly severe, and haze occurred frequently. Demand for the economy and environmental protection of the power machine is becoming more and more stringent. As an important member of the power machine, diesel engine’s technological innovation has been paid more and more attention by scholars. As the most important part of the diesel engine, the injector has a great influence on the emission and dynamic performance of the engine. The advanced injection system based on the group injection hole can make the fuel achieve high quality atomization under the lower injection pressure. The processing technology of small holes in injector is becoming more and more mature. Besides, the feasibility of group-hole nozzle technology is increasing day by day. It is increasingly recognized by the academia and industry.This study firstly illustrated the background of fuel atomization, then introduced the development of the experimental measurement and spray model. Based on the AVL-FIRE fluid calculation software, an accurate mathematical model of the internal flow field is established. The reliability of the calculation model is verified by comparing with the experimental data. On the basis of this model, the two-flow in the group-hole nozzle is calculated. The influences of injection pressure, distance between adjacent holes, inlet rounded radius of nozzle orifice, nozzle length, disturbed area, varying longitudinal cross-section and cross angles were analyzed. Analytical indexes included internal pressure, velocity, turbulent kinetic energy distribution of liquid fuel, volume fraction, mass flow and mass flow coefficient. The results showed that compared to the multi-hole nozzle group-hole nozzle had larger mass flow. The mass flow and the flow coefficient increased with the increase of the cross angle of the group-hole nozzle, the average velocity had a modest rise and the turbulent kinetic energy decreased. In addition, this study designed disturbed area, increasing the diameter of disturbed area can lead to the increase of the mass flow and mass flow coefficient. However, the mean velocity and turbulent kinetic energy of the outlet reduced when the diameter of disturbed area is 0.0015 mm.In this study, we designed and processed the group-hole nozzle. Relevant sizes were measured by using Mycrona measuring instrument. Spraying experiment was carried out on the high pressure common rail test platform after the nozzle had reached the relevant requirements of the test. The spray pattern under atmospheric pressure was observed by using Motion ProTMin10000 high speed digital video camera. The influences of different injection pressure and nozzle types on the spray were compared and analyzed. According to the test results, a more accurate calculation model was built. The mass flow in the nozzle was acted as the boundary condition, and the accuracy of the model was verified by comparing the penetration distance and spray pattern. Using the validated calculation models, constant volume chamber’ condition, effects of R/D(Curvature Radius of the Inlet Orifice/Orifice Diameter)and L/D(Nozzle Length/Orifice Diameter) on spray characteristics were studied numerically. The increased R/D can increase SMD, reduce the spray penetration, cut evaporation mass and slow droplets velocity. When the value of R/D is 0.12, the spray characteristics reach a constant state due to cavitation elimination. The spray characteristics of the group-hole nozzle were similar to that of single-hole nozzle, but the atomizing performance of group-hole was slightly better than that of single one. R/D had same effect on spray characteristics of group hole nozzle and single nozzle. L/D increased, SMD increased, the spray penetration increased, and the evaporation mass decreased. |
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