An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirl‐type injector, was carried out at an injection pressure and duration of 7.0 ...MPa and 3.0 ms, respectively, in an optically accessible vessel, at atmospheric pressure and ambient temperature. The temporal and spatial spray evolution was investigated in terms of global spray structure, interaction with the external gas, time‐resolved droplet size and velocity distribution.
The measurements were carried out with an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. Digital image processing software for the study of the global parameters of the spray was used. A particle Doppler analyzer (PDA) system was used to estimate the local droplet size and velocity as function of the radial coordinate and distance from the nozzle. A laser light extinction technique was applied to investigate the region close to the nozzle up to 5 mm.
The spray emerging from the nozzle, at an early time, showed a hollow‐cone type of structure because of the swirl motion of the fuel in the orifice that produces a rotational momentum at the nozzle exit. The spray starts with a central pre‐injection phase followed, later, by the main body characterized by a large cone angle. The interaction of the fuel with the gas in the spray chamber was evidenced; curls on the external boundary and re‐filling of the central part of the cone, during the second part of the injection, were observed.
Measurements at different locations within the spray showed high values of the droplet velocity close to the nozzle exit at an early time. These high values were found downstream in the final stage of injection. Radial velocities were present along the entire injection process with an outer direction in the first stage, while an inner direction was observed in the second part. The droplet size distribution showed increasing values along the injector axis and towards the periphery of the spray.
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