Improving fuel economy and reducing exhaust emissions of automobile engines have become very important. The direct injection gasoline engine has the advantage of reduced fuel consumption, but it also has disadvantages related to exhaust emissions. Weak mixing of fuel with air due to short mixing time and fuel liquid-film adhering to the engine cylinder walls cause emission problems. To reduce these emissions, injectors need to provide fine atomization, low fuel penetration (length of fuel spray), and spray formation control. In this study, we developed a multi-swirl nozzle that forms a thin liquid-film at the nozzle outlet for fine atomization; the thin liquid-film easily breaks up into small droplets. We investigated the fuel spray characteristics of these nozzles experimentally and numerically. Using a long-distance microscope, we found that a liquid-film formed at the nozzle outlet even if its diameter was small. This is an effect of the centrifugal force from the swirl flow. Experimental results also showed that the multi-swirl nozzle reduced the size of coarse droplets (irregular, large droplets) and shortened fuel penetration. We also simulated numerically the fuel flow of the multi-swirl nozzle. Numerical analysis described the swirling flow that the multi-swirl nozzle generated above the nozzle inlet and the thin liquid-film at the nozzle outlet.

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