Experimental Investigation of the Primary Spray Development of GDI Injectors for Different Nozzle Geometries

The optimization of the mixture formation represents great potential to decrease fuel consumption and emissions of spark-ignition engines. The injector and the nozzle are of major importance in this concern. In order to adjust the nozzle geometry according to the requirements an understanding of the physical transactions in the fuel spray is essential. In particular, the primary spray break-up is still described inadequately due to the difficult accessibility with optical measuring instruments.

This paper presents a methodology for the characterization of the nozzle-near spray development, which substantially influences the entire spray shape. Single hole injectors of the gasoline direct injection (GDI) with different nozzle hole geometries have been investigated in a high pressure chamber by using the MIE scattering technique. To examine the spray very close to the nozzle exit a long-distance microscope in combination with a Nd:YAG-laser was used. Among the qualitative evaluation of the images the selection and representation of quantitative parameters which allow a characterization of the nozzle is carried out. In this study the characteristic parameters are the droplet number, droplet size, spray area and the circularity of the droplets. By gathering two time shifted images it was possible to calculate a velocity field near the nozzle exit using a cross correlation algorithm. The measurements show unambiguous differences in the flow pattern created by the individual nozzle hole geometries. The methodology presented in this study shows great potentials to characterize the primary spray development of different injectors and to draw conclusions about the internal nozzle flow. Comparative considerations between different nozzles are possible.