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We propose a flat spray pattern to improve conventional stratified-charge combustion systems in a direct-injection (DI) gasoline engine. Swirl-type DI fuel injectors with a V-groove cut orifice nozzle (V-groove nozzle) and a rectangular-groove cut orifice nozzle (U-groove nozzle) are newly designed. We examine experimentally the characteristics of newly designed injector nozzles under various ambient pressure and fuel pressure conditions. The fuel spray characteristics were tested inside an experimental pressure chamber. The resulting spray patterns were illuminated by YAG-laser sheet and recorded by CCD cameras. The atomization of fuel-spray in the V-groove and U-groove nozzle was also investigated. These experiments showed that the V-groove and the U-groove nozzles generate a well-atomized flat fuel-spray pattern that can be controlled by the orifice-depth and it is robust under ambient pressure variations.

Fuel-spray pattern is one of the most critical factors for obtaining stable combustion. A DI fuel injector in which the fuel-spray pattern can be easily controlled and predicted is therefore essential. Our main goal is to develop a fuel-spray pattern control method that takes into account the influences of ambient pressure and fuel pressure. After deciding how to incline and split the fuel spray, we designed an L-cut orifice nozzle (L-step nozzle) based on a swirl-type injector. We investigated the fuel-spray pattern of the newly designed injector both experimentally and numerically. Experimentally, the L-step nozzle injector was used to spray fuel into an experimental pressure chamber. The resulting spray patterns were visualized by YAG-laser sheet and recorded by CCD cameras. The spray formation was analyzed and the spray patterns were evaluated in terms of spray angle and penetration length. Atomization from the spray in the L-step nozzle injector was also investigated.

We examine experimentally and numerically the influences of nozzle geometry on spray angle and penetration length. Swirl-type DI fuel injectors with an L-cut orifice nozzle (L-type) and a taper-cut orifice nozzle (Taper-type) are newly designed. The new injectors are used to spray fuel inside an experimental pressure chamber. The resulting spray patterns are visualized by YAG-laser sheet and recorded by CCD cameras. These experiments showed that both the L-type and taper-type nozzles can produce an inclined fuel-spray pattern. Furthermore, the fuel-spray pattern can be controlled by changing the depth of the orifice in both nozzles. During the development of the new nozzles, a CFD code for predicting the spray shape are also developed. By comparing the calculated results to the experiments, it was shown that the CFD code can predict the spray angle with reasonable accuracy. The spray angle was found to be strongly dependent on the air void geometry formed inside the orifice.

The effect of fuel injection fuel atomization on engine performance has been studied in order to improve fuel economy and emission characteristrics. The fuel swirl method for injector atomization was studied both by fuel flow analysis and prototype experimentation. The goal of the studies was to develop fine fuel atomization over a wide engine operation range. As a result of our studies, it has been concluded that a desirable atomization can be obtained when the fuel is swirled in a circumferential direction and the swirl number is greater than 0.6. Protoype injectors applying these principles have been developed and tested in passenger car engines. The test results show that 3% improvement in fuel consumption and 8% reduction in hydro-carbon emission can be expected when fine atomization injectors are installed.