Diagnostics For The Spray Characteristics Of Intersecting Hole Injectior And Outwards-opening Injector

As the gasoline direct injection engine and diesel engine HCCI/PCCI combustion system were proposed, premixed combustion concept has been enriched, meanwhile, the fuel injection technologies and researches of spray characteristics get more and more attention and rapid development. For the spray-guided concept of DI gasoline engines, spray characteristics are very important for the mixture preparation, which should own well-atomized performance, large spray volume and short spray tip penetration. On the other hand, HCCI/PCCI combustion system based on diesel fuel also need these spray characteristics. Due to low volatile and high viscosity of diesel fuel, early injection of diesel engines has to face more complicated problems relative to DI gasoline engines. It is easy to cause the "wall wetting" and engine oil dilution for the overlong spray tip penetration in the early stage of compression stroke. Meanwhile, the insufficient evaporation of oil film and many large-size droplets caused by impingement also play a negative role in the field of fuel economy and emission performance. Therefore, it is necessary to develop a new injector that owns the spray characteristics of well-atomized performance, large spray volume and short spray tip penetration, not only for diesel engines but also for the DI gasoline engines.For this backdrop, this dissertation focuses on the spray characteristics of outwards-opening injector and new V-type intersecting hole injector. The visualization research on the hollow cone spray through the outwards-opening pintle-type injector activated by piezo was carried out by means of high-speed photography. The results show that the effects of ambient pressure, injection pressure and needle lift on the spray angle is very small. The actual spray angles keep constant with the designed spray angles (pintle seat spread angle) in different experimental conditions. The spray tip penetration reduces significantly when the ambient pressure increases from0.1MPa to1.1MPa, even the injection pressure of20MPa. Meanwhile, this dissertation proposed the concept of spray volume enhancement ratio, namely the volume ratio of formed spray and injected fuel, in order to estimate the effects of variable characteristic parameters on spray distribution and atomization. The microscopic feature of the spray in the early stage of injection was observed by using super high-speed camera. It is noticed that the spray consists of many independent strings, instead of a continual structure. For this reason, it can be speculated that the string structure promotes fuel/air interaction and spray atomization significantly. Secondly, velocity field characteristics on axial cross-sections of conical sprays from the piezo outwards-opening pintle-type injectors under different chamber conditions are measured and analyzed by means of Particle Image Velocimetry (PIV). Experimental results reveal that an intense recirculation region is formed in the vicinity of nozzle by the aerodynamic action. The large-scale vortices formed near the nozzle, namely the vortex A and vortex B, not only promote air entrainment and atomization, but also play an important role to mixture distribution after injection. The effects of injection pressure, ambient pressure, needle lift and designed spray angle on the large-scale air vortex A and B are investigated. Moreover, the root mean square calculation of velocity results is carried out. The turbulence intensity characteristic of spray field and the influence of it on mixture distribution are analyzed further according to the standard deviation fluctuation of node velocities.In addition, droplet velocity and size characteristics of conical spray injected through the piezo pintle-type injectors are measured and analyzed by means of Phase Doppler Anemometry (PDA). Experimental results indicate that the variation of ambient pressure not only significantly affects the spray tip penetration and the velocity characteristics of spray field, but also affects the droplet size obviously. From the perspective of atomization and mixture preparation quality, the effects of ambient pressure, injection pressure and needle lift on the droplet characteristics, i.e. droplet velocities and sizes, are analyzed. Time dividing method is used to study the droplets characteristics in four parts of spray respectively. The result proves that the leading edge of spray contains many droplets with high velocity and large size. However, the AMD and SMD of fuel droplets in the spray field remain at a stable level when the droplet velocity becomes zero after fuel injection.The well atomization and the short spray tip penetration of the hollow cone spray through the piezo outwards-opening injector is proved, but the cost of this kind of injector is very high, and the spray performance in the condition of diesel high-pressure injection system still needs to be studied. The increased injection pressure for improving atomization challenges the seal and reliability of the fuel supply system, as well as the power consumption and cost problem. Therefore, it is necessary to develop a new injector, which can reach the same atomization level with a lower injection pressure, or better atomization with the same injection pressure relative the conventional injector. Meanwhile, the short spray tip penetration is another important precondition. For these reasons, a new nozzle structure called V-type intersecting hole nozzle is proposed in this dissertation. According to the different injection pressure levels of diesel engines and DI gasoline engines, the experiment is divided into the high-pressure and low-pressure parts. The macroscopic feature of the fan-shaped spray injected through the V-type intersecting hole nozzle is observed and measured in the environment of constant volume vessel. Furthermore, combing with the spray volume enhancement ratio, the detailed droplet size results obtained by PDPA is used for the further analysis on the effects of ambient pressure, injection pressure and intersecting angle on atomization of the fan-shaped spray. In addition, numerical simulation is carried out to analyze the effects of the intersecting angle on the velocity characteristics, as well as cavitation in AVL-FIRE environment. Experimental results reveal that the radial liquid internal force which is the reacting force of wall is the major reason for the larger spray angle. And the size difference of the liquid internal force in X and Y directions leads to the difference of spray radial growth rate, which causes the formation of the fan-shaped spray finally.