Combustion timing variability in a light boosted controlled auto-ignition engine with direct fuel injection

A single cylinder engine with ability to controlled auto-ignition (CAI) combustion was used in order to study cycle-by-cycle combustion variability. The engine was operated in negative valve overlap (NVO) mode resulting with an internal gas re-circulation. Direct gasoline injection was applied in a single dose during the NVO period. Various intake pressures were applied, ranging from atmospheric aspiration to 0.15 MPa boost pressure. The combustion timing was examined in terms of 5 % mass fraction burnt (MFB). Experimental results showed that cyclic variations of 5 % MFB demonstrate deterministic oscillations under boosted operation. Cycle-by-cycle variability was associated with NVO heat release feedback to the main combustion process. Moreover intermittent combustion behavior was demonstrated with the use of recurrence plots.