Effects of key factors on the engine combustion mode switching between HCCI and SI

A technical strategy for a rapid and smooth switching between spark ignition (SI) mode and homogeneous charge compression ignition (HCCI) mode on a gasoline direct injection engine has been proposed and investigated, which involves an electrohydraulic two-stage cam profile mechanism and special injection strategies. The key factors that affect the HCCI/SI mode switching processes were analyzed on the basis of transient engine tests in terms of combustion parameters and exhaust emissions. It is shown that special care should be taken on the engine functionalities during the mode switching from SI to HCCI, which appears to be more difficult, and simultaneous control of the key parameters such as injection mass, injection timing, and spark timing is required. Various strategies and their general criteria for the mode switching were discussed. An optimized combination of selected control strategies has been demonstrated with a satisfactory switching process completed in ten engine cycles, without any abnormal combustion cycles in between.