Using ion current sensing to interpret gasoline HCCI combustion processes

Homogeneous charge compression ignition (HCCI), combustion has the potential to be highly efficient and to produce low NOx, carbon dioxide and particulate matter emissions, but experiences problems with cold start, running at idle and producing high power density. A solution to these is to operate the engine in a ‘hybrid mode’, where the engine operates in spark ignition mode at cold start, idle and high loads and HCCI mode elsewhere during the drive cycle, demanding a seamless transition between the two modes of combustion through spark assisted controlled auto ignition. Moreover; HCCI requires considerable control to maintain consistent start of combustion and heat release rate, which has thus far limited HCCI’s practical application. In order to provide a suitable control method, a feedback signal is required. This paper will investigate the use of an ion-current sensor in HCCI combustion in order to extract and quantify combustion measurants, with particular reference to control applications. A presentation of results of ion-current sensing for monitoring combustion under steady state operation, over a variety of speeds and trapped residual gas amounts is made. The results show that estimation of cylinder pressure parameters through the ion signal with promising accuracy is shown, and ion-current is proven to be a cost effective and adequately informative feedback signal for both SI and HCCI engine control.