Gasoline Direct Injection (GDI) engines have developed rapidly in recent years driven by fuel efficiency and consumption requirements, but face challenges such as injector deposits and particulate emissions compared to Port Fuel Injection (PFI) engines. While the mechanisms of GDI injector deposits formation and that of particulate emissions have been respectively revealed well, the impact of GDI injector deposits and their relation to particulate emissions have not yet been understood very well through systematic approach to investigate vehicle emissions together with injector spray analysis.
In this paper, an experimental study was conducted on a GDI vehicle produced by a Chinese Original Equipment Manufacturer (OEM) and an optical spray test bench to determine the impact of injector deposits on spray and particulate emissions. The vehicle, with the mileage over 13,000 km, was subject to emissions tests such as gaseous emissions, particulate mass (PM), and fuel economy on a chassis dynamometer under the new European driving cycle (NEDC), then re-tested after having its injectors replaced. Deposit morphology and spray characteristic experiments including spray angle, penetration, droplet diameter and velocity distribution as well as near-field spray imaging were also conducted for the coked injectors both before and after cleaning.
The results demonstrated GDI injectors were prone to form deposits which resulted in smaller spray angles, longer penetration, smaller droplet diameter, and higher velocity as well as severe leakage found at the end of injection. These results can well explain why injector deposits resulted in much higher particulate emissions (increased 376%) as well as higher fuel consumption (3%) after just 13,000km of mileage accumulation.