General Motors recently demonstrated two driveable test vehicles powered by a Homogeneous Charge Compression Ignition (HCCI) engine. HCCI combustion has the potential of a significant fuel economy benefit with reduced after-treatment cost. However, the biggest challenge of realizing HCCI in vehicle applications is controlling the combustion process. Without a direct trigger mechanism for HCCI's flameless combustion, the in-cylinder mixture composition and temperature must be tightly controlled in order to achieve robust HCCI combustion.
The control architecture and strategy that was implemented in the demo vehicles is presented in this paper. Both demo vehicles, one with automatic transmission and the other one with manual transmission, are powered by a 2.2-liter HCCI engine that features a central direct-injection system, variable valve lift on both intake and exhaust valves, dual electric camshaft phasers and individual cylinder pressure transducers.
The development of the HCCI engine controller starts with a stability analysis of the HCCI combustion process. Based on the stability analysis, operating set-points (e.g., EGR rate, air-fuel ratio, etc.) for robust HCCI combustion were determined. The engine controller was then designed to follow those set-points in HCCI combustion mode as well as manage transitions to and from SI combustion mode, which is necessary because conventional SI combustion is still currently required in high-load operations. The engine controller has been validated on both single-cylinder HCCI engine and multi-cylinder HCCI engine in the engine test cell. Finally, some test results from demo vehicles are included.