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The present work aims at providing information about the spray structure and its interaction with the tumble motion generated by the intake ducts of a prototype gasoline direct injection (GDI) engine. The investigation was carried out characterizing the fuel evolution within a prototype cylinder, under steady state flow conditions, by the 2-D laser imaging and Particle Image Velocimetry (PIV) techniques. The results offer a database about the spatial and temporal evolution of fuel spray that can validate numerical simulation for prediction of mixture formation and combustion in direct injection gasoline engines. Experiments were taken using a common rail injection system able to work at a maximum pressure of 12 MPa, a swirled type injector with a nozzle diameter of 0.55 mm and a nominal cone angle of 50°. The investigation was conducted by applying the 2-D imaging and the PIV techniques in a flow test rig, designed for capturing the tumble motion in a prototype cylinder. The system included a blower, which supplied the intake flow rate, and a prototype 4-valve direct injection gasoline engine head modified to lay down the swirled-type injector. Tests were taken, on a plane crossing the cylinder and the injector axes, spraying the fuel at Pinj = 5, 8, and 10 MPa for an injection interval of Δt=3 ms. The results provided detailed information on the pre- and main spray evolution. At the first stage of injection, the fuel jet depicted a dense liquid column with a very small cone angle while a transition to a spray hollow-cone structure was observed at later injection time. Images of the interaction of the fuel with the tumble motion displayed, firstly, a fuel jet that traveled as a compact liquid column not affected by the tumble motion within the cylinder because of its high momentum. At later injection time, the fuel was strongly distorted by the tumble motion with the formation of secondary droplets clusters that detached from the main jet and were dispersed within the cylinder. Images highlighted a spray that penetrated with a cone angle smaller than that observed under stagnant conditions. PIV measurements showed a fuel jet having a velocity distribution profile that endorses the liquid column like typical of the pre-spray penetration. When the fuel jet reached the steady cone angle, PIV results depicted an intense momentum exchange with the tumble airflow that becomes the controlling parameter for the jet break-up and the dispersion of droplets within the cylinder.
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