Method of ion current detection for HCCI combustion on SI/HCCI dual mode engine

With the advantages of high thermal efficiency and extra low NOx and soot emissions, homogeneous charge compression ignition (HCCI) combustion has become a promising combustion method. Comparing with the SI engine or diesel engine, it is hardly to control combustion phase and combustion period on a HCCI engine directly. Hence, sensing of combustion phase and combustion state is very important for HCCI engine control. In this paper a method of detecting ion current signal as the feedback of combustion characters was discussed through a series of experiments on a gasoline HCCI engine. When the engine operated in pure HCCI mode, the ion current was measured and several parameters were abstracted from ion current waveform in order to investigate the relationship between the ion current and the combustion characters. Simultaneously, the in-cylinder pressure was measured and the rate of heat release was calculated. Experiment results show that there is a strong correction between HCCI combustion phasing and ion current signal. On the other hand, the relationship between ion current and combustion phasing was also discussed when the engine operated under spark assisted HCCI mode. Thus through a set of parameter definition the influence of ignition coil discharge to ion current also be researched.