An Experimental Study of Microscopic Spray Characteristics of a GDI Injector Using Phase Doppler Interferometry

Gasoline Direct Injection (GDI) engine is known for its higher power and higher thermal efficiency. Researchers are steadily determining and resolving the problems of fuel injection in a GDI engine. In order to meet the stringent emission norms such as PM and NO_x emitted by a GDI engine, it is necessary to investigate the microscopic spray characteristics and fuel-air mixing process. This paper aims to share the fundamental knowledge of the interacting mixture preparation mechanisms at the wide range of fuel injection pressures. The investigations were carried out at five different fuel injection pressures viz: 40, 80, 120, 160, 200 bar, for 24 mg fuel per injection. A high speed CCD camera was used to determine the macroscopic spray characteristics of the GDI injector. It was found that spray penetration length increased with increasing fuel injection pressure. Phase Doppler Interferometry (PDI) was used to determine the droplet size and droplet velocity for different test fuels. In the end, Sauter Mean Diameter (SMD) and Probability Density Function (PDF) and diameter verses velocity curves were plotted, which gave better understanding of the behavior of fuel injection pressures responsible for improved fuel-air mixture. In the PDF, the shifting of the peak towards left was found to be desirable for better fuel-air mixture. It was observed E15 is better fuel for pressure range of 40-160 bar and gasoline for 200 bar pressure. Droplet sizes with different injection pressures in turn helped in minimizing stringent emission norms.