The Microstructure Characteristics Of The Spray Of A Direct-injection Gasoline Signal-hole Injector

Direct injection technology is one of the effective ways to improve the fueleconomy of spark ignition gasoline engines. Fuel spray is a key factor influencing thecombustion and emission characteristics of direct-injection spark ignition (DISI)gasoline engines. Therefore, it is significant to investigate the spray breakup processesunder the conditions of high injection pressure. Investigation was conducted asfollow:A specific constant vessel used for the microscopic magnification of the gasolinespray of a single-hole injector for direct injection and its optical system were set up.On the basis of the MATLAB software, a code to recognise the features of sprayimages was programmed. Microscopic spray images were recorded by means of ahigh-speed digital camera. The results show that,The development of near-field spray cone angle close to the injector exitexperiences sharp decrease, intensive fluctuation, slight fluctuation and gradual risewith time. Injection pressure difference evidently affects the vertical velocity of sprayat the beginning of fuel injection. In high pressure difference condition, the change inspray cone angle experiences the zone dominated by cavitation number, transient zoneand the one dominated by ambient pressure with cavitation number. With the increaseof cavitation number, the near-field spray cone angle decreases and then increases.The length of surface waves on the jet become shorter and its frequency becomeshigher with increasing ambient pressure. Fuel film is formed at the hole exit of theinjector at the end stage of injection and is finally broken up into the droplets with bigdiameter.The degree of spray breakup is different in various regions in the jet. After theprimary breakup, large-scale fuel droplets appear near the axes of spray and thenumber of droplets increases with increased ambient pressure. The amount of dropletsdecrease along the radial direction and the spray breakup is complete on the boundarybetween the spray plume and ambient air. During the injection processes, thedistribution of small fuel droplets is uneven on the boundary of the spray plume andthe fishbone shaped spray is formed. The secondary breakup of a droplet is a process dominated by various breakup mechanisms. There are a lot of droplets movingdownwards due to droplet inertia and horizontally because of entrainment at the sametime.