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The government has been imposing a stricter diesel engine efficiency standard to reduce carbon dioxide, NOx and other particulate emissions. Diesel combustion improvement is a major concern, and many researchers have examined diesel combustion and its sprays. One possible method to solve the technical problems is applying the Variable Orifice Nozzle (VON) to fuel injection systems. The VON, which nozzle cross-sectional area is changed continuously, has been developed for direct injection (DI) diesel engines. The orifice changing mechanism is composed mainly of a rotary valve, drive shaft and small pulse motor. The VON's standard deviation (SD) of injection quantity in injection pump operation range is the same as the conventional hole nozzle's due to the rotary valve that is fixed by a spring. The smaller orifice of the VON has produced a higher injection pressure and produced a longer injection duration than that of a larger orifice.

The Variable Orifice Nozzle (VON), has been developed to improve diesel combustion by changing the cross-sectional area of the injection hole. The area of the nozzle orifice is continuously controlled by the rotary valve, one component of the VON. The discharge coefficient of the VON was increased by simulating an internal flow in the nozzle tip. The VON performances were evaluated by its rate of injection, injection pressure, spray droplet diameter and instantaneous photographs taken by a high speed camera. These results show that, injection characteristics and spray patterns respond to the nozzle orifice area which is changed by the rotary valve from larger to smaller. The orifice area controlled nozzle provides higher maximum pressure and a longer injection duration than the conventional hole nozzle without full-load point of the injection pump. A smaller nozzle orifice has a wider spray angle compared with larger nozzle orifice.

The motion and distribution of the cloud cavitation in a fuel injection pump are calculated. Numerical code consists of a set of equations in which the radial and transverse motion of bubbles are considered. The computational results examine that bubbles are trapped in the vortex and formed the bubble cloud. These results show qualitatively good agreement with experimental ones. Furthermore collapse of cloud cavitation is simulated numerically. The computational results reveal that the emitted impulsive pressure in the center of cloud exceeds a few GPa and becomes a few hundred times larger than the pressure from a single bubble collapse.

An Eulerian model of evaporating transient sprays and a new method to describe air-atomization near the injector exit to predict the mean size and velocity of droplets have been developed to study the influence of operating conditions of an air-assist hollow-cone injector and the influence of fuel atomization on the spray structure. Good agreement between the results of the computation and experiment in terms of spray shape has been achieved. The numerical results show the typical structure of sprays from the air-assisted fuel injector and show the influence of atomization on the structure.