An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirled-type injector, has been carried out at the 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 has been investigated in terms of global spray structure, interaction with the external gas, time resolved droplet size and velocity distribution. The measurements have been carried out by an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. A digital image processing software for the study of the global parameters of the spray has been used. A particle Doppler analyzer (PDA) system has been 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 has been applied to investigate the region close to the nozzle up to 5 mm. The spray emerging from the nozzle, at early time, has shown a hollow-cone type 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 has been evidenced; curls on the external boundary and re-filling of the central part of the cone, during the second part of injection, have been observed. Measurements at different locations within the spray have shown high values of droplets velocity close to the nozzle exit at early time. These high values have been found downstream in the final stage of injection. Radial velocities are present along the entire injection process with an outer direction in the first stage, while an inner direction has been observed in the second part. The droplet size distribution has shown increasing values along the injector axis and toward the periphery of the spray.
Droplet size and velocity distributions of a transient hollow-cone spray for GDI engines
Allocca L;Valentino G
2001
Abstract
An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirled-type injector, has been carried out at the 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 has been investigated in terms of global spray structure, interaction with the external gas, time resolved droplet size and velocity distribution. The measurements have been carried out by an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. A digital image processing software for the study of the global parameters of the spray has been used. A particle Doppler analyzer (PDA) system has been 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 has been applied to investigate the region close to the nozzle up to 5 mm. The spray emerging from the nozzle, at early time, has shown a hollow-cone type 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 has been evidenced; curls on the external boundary and re-filling of the central part of the cone, during the second part of injection, have been observed. Measurements at different locations within the spray have shown high values of droplets velocity close to the nozzle exit at early time. These high values have been found downstream in the final stage of injection. Radial velocities are present along the entire injection process with an outer direction in the first stage, while an inner direction has been observed in the second part. The droplet size distribution has shown increasing values along the injector axis and toward the periphery of the spray.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
