Strategies for enlarging the operational range of an HCCI gasoline engine

The homogeneous charge compression ignition (HCCI) engine concept (also known as the controlled auto ignition (CAI) engine concept) has the potential to be highly efficient and to produce low NOx, carbon dioxide and particulate matter emissions. However, it experiences problems with a restricted operating range by misfiring at low load and by high rates of heat release and misfire at high load and hence is seen as a low- to medium-load concept. For commercial use there is a need to expand the HCCI operational range to cover greater parts of contemporary driving cycles such as NEDC, FTP-75 and Japan 10-15, without switching to conventional spark ignition (SI) combustion mode. The aim of this paper is to present an investigation into and the development of various strategies for enlarging the HCCI operational range enabled mainly by using fully variable valve train (Lotus AVTTM). These include recompression, rebreathing, a combination of the two, early or late intake valve closure and exhaust valve opening, increasing or reducing valve lift and duration, together with adjusting the coolant temperature. The potential, efficiency and practical implementation of each of the strategies were analysed from the experimental results obtained.