Development of a Gasoline Engine System Using HCCI Technology - The Concept and the Test Results

Homogeneous-charge compression-ignition (HCCI) technology has high potential to significantly reduce fuel consumption and NOx emissions over PFI engines. Control of the HCCI combustion process over the full range of conventional PFI operating conditions, however, has been a challenge. This study describes an HCCI-SI dual-mode engine system proposal based on new approaches to optimize the engine performance. A 0.658L single-cylinder engine was built and tested using these concepts. The engine was operated in HCCI mode from idle to 5.5 bar NMEP and up to 4750 rpm. NSFC in HCCI mode was about 175 g/kWh over most of the operating range except at very low load or near the high load boundary. At a part load of 1500 rpm and an equivalent BMEP of 2.62 bar, net indicated fuel efficiency was 50% higher than PFI engines and 30% higher than a prototype SC-DISI engine. Net specific NOx emissions were lower than 0.1 g/kWh below 4 bar NMEP, approximately two orders of magnitude lower than those from both SC-DISI and PFI engines. Boosting the intake pressure at loads above 4 bar NMEP leaned the mixture, significantly reducing NOx emissions and expanding the HCCI high-load operating region. Engine operation at light loads increased CO emissions sharply, but with both intake throttling and advanced combustion timing, CO emissions were reduced. Other HCCI combustion control issues and strategies were also investigated, such as the available thermal energy for intake heating at light load. Unboosted, the engine was tested in SI mode up to 7 bar NMEP with fuel efficiency higher than conventional PFI engines. Boosted with 92 RON fuel, the engine was operated up to 11.7 bar GMEP.