Hybrid SI-HCCI combustion modes and the potential for control

An improvement in the fuel efficiency of gasoline engines is necessary to realize a significant reduction in U.S. energy usage. Homogeneous charge compression ignition (HCCI) in internal combustion engines is of considerable interest because of the potential reductions in flame temperature and nitrogen oxide emissions as well as potential fuel economy improvements resulting from unthrottled operation, faster heat release, and reduced heat-transfer losses. Unfortunately for many transportation applications, HCCI may not be possible or practical under the full range of speed and load conditions. Thus, the most important technical developments needed to achieve wide-spread HCCI utilization are expanding the operational range and the ability to switch between HCCI and traditional propagating flame (e.g., spark ignition) combustion as power and speed change. Several recent publications and presentations have begun to address the control issues but have not focused on the fundamental nature of the transition dynamics associated with switching from SI to HCCI combustion. The development of both combustionmode switching and stabilization technologies requires that the fundamental nature of the transition be well understood, especially in the context of realistic engine conditions.