Comparative Research on Emission Characteristic and Combustion Characteristic of Gasoline Direct Injection and Port Fuel Injection for Free-Piston Linear Generator

As a new type of energy, free-piston linear generator (FPLG) attracts more research on its stable operation and power performance, while less on its combustion and emission performance. So, in this paper, the emission characteristics of FPLG in two different modes are studied through a port fuel injection (PFI) mode which was verified by the experiment and a gasoline direct injection (GDI) mode. The results showed that: both the GDI mode and the PFI mode produced large amounts of nitrogen oxide (NOx) during the working process. But the GDI mode produced before the PFI mode and it produced nearly 2 times than the PFI mode. However, the formation rate of NOx in GDI mode is much lower than that in PFI mode. Meanwhile, in both modes, 90% of NO_X was generated in the cylinder at the temperature higher than 1750K, and only about 10% of NO_X was generated at a temperature lower than 1750K. As for carbon smoke (SOOT), accorded to the research results, the SOOT production in GDI mode was 25% lower than that in PFI mode, and the SOOT production rate in GDI mode decreased in certain stage. On the contrary, this phenomenon did not occur in PFI mode. However, the SOOT generated in both modes can be oxidized rapidly at a later stage to reach zero emissions.