Measurement And Simulation Of Injection Rate Of Each Hole Of Injector Based On Spray Momentum Flux

As the regulations of emissions and fuel consumption are becoming more stringent,diesel engines are improved more clean,efficient and energy-saving.The fuel supply and injection system,its pressure is about 200 MPa or even higher is required to fulfill the increasingly strict emission regulations.Consequently,the common rail technique has become the mainstream in diesel engines because of its unique technical advantages,where the injector,as the final actuator connecting upstream high pressure common rail system and downstream fuel injection,is critical.There are injection characteristic differences among each hole,due to the differences in nozzle structure,the process error and the complicated movement of the needle.These affect the atomization of fuel and formation of the mixture.The economy,emissions,and vibration and noise of diesel engines are affected the fluctuation of the injection rate due to the complex multi-physics coupling of the high-pressure common rail fuel system.Therefore,for large diesel engine injectors,the study of the difference of injection characteristics of each hole and their cyclic variation has great significance to optimizing the design and manufacture of the injector.The main contents of the thesis are as follows:（1）A measurement system for transient injection characteristics of each nozzle hole was designed and set up based on the momentum conservation and Bernoulli’s theorem.The measurement system could acquire the instantaneous injection rates of each nozzle hole in the multi-hole injector simultaneously,and realize the cyclic acquisition of multiple injection in the meantime.Finally,the accuracy and reliability of the test system are validated（2）The two types of force sensors（Strain sensor and Piezoelectric sensor）are also analyzed and compared with one another.The influence of the force sensors’installed position and angle（location in the set-up）on measured results,were analyzed.The optimum position that ensures accuracy of the results is determined.Piezoelectric force sensor has better dynamic response to meet the requirements of the test system.The accuracy of the results is affected by the installation position of the sensors.A distance range of 10-20 mm（between nozzle hole exit and sensor surface）and angle within±6°were determined,which are adequate for the acquisition of reliable experimental data.The errors between the momentum flux method and the EFS single injection measuring instrument under different injection pressures and injection pulse width were within5%.（3）The injection characteristics of heavy-duty diesel injectors with different nozzle structures were measured by the established fuel injection rate test system.The influences of injection pressure,injection pulse width and hole diameters on injection rate of each hole,nozzle-to-nozzle variability coefficient and hole-to-hole variability coefficient of injection quantity were also analyzed.With the increasing of the injection pulse width,the cycle injection quantities are increased and the cycle to cycle to cycle variation of the injection quantities are reduced.As the injection pressure increased,the consistency of each hole is improved.The injection pressure has little effect on the discharge coefficient when the needle is at the maximum lift.Besides,when the diameters of hole are larger,the injection rate and the discharge coefficient are higher.（4）A three-dimensional（3D）two phases model for the internal fluid domain of the nozzle was established and verified based on the experiment results.The internal flow characteristics of the nozzle（mainly including velocity,pressure,and cavitation）were analyzed.The flow characteristics inside the nozzle with different nozzle structures(taper coefficientK_factor,orifice inclination)were also studied.The results show that,the tapered nozzle hole helps to improve the flow characteristics of the nozzle.With the increasing ofK_factor,the injection rate is increased.When the nozzle inclination angle is larger,the injection rate is smaller.