Investigation of the potential for gasoline direct injection (GDI) in a small displacement four-stroke engine

The primary goal of this research was to assess the potential benefits of gasoline direct injection (GDI) in term of fuel economy, efficiency and emissions in a small displacement, water cooled engine. A 747cc V-twin engine was installed in a test cell on a 25 kW dynamometer. The test cell was adapted with a water cooling system, an extended two-stage fuel system with low and high fuel pressure capability, a control system, a new data acquisition system and a new 5-gas analyzer. The engine was modified to be operated either port-fuel injected (PFI) or direct-injected (DI) in cylinder 1. To do so, the engine head was outfitted with a spark plug insert that held the injector and with a new spark plug location. High-speed in-cylinder pressure transducers were added to the cylinder heads. The injector was chosen from a range of production direct injectors after thorough injector characterization in atmospheric conditions, with and without gas flow. The engine was equipped with an incremental optical encoder and a Hall-effect cam sensor on the cam wheel for cycle differentiation. The engine was operated at light and part load conditions. The behavior of the GDI combustion was studied over a range of spark timings, start of injection timings and injection pressures. A same[1]cylinder comparison was performed between the GDI and PFI modes. Overall, the GDI configuration showed a potential for NOx reduction without impacting engine efficiency. The engine was successfully operated at low injection pressure, and it was demonstrated that reducing injection pressure did not affect the engine’s performances in most cases. A potential was shown for higher load based on a later SOI timing.