The present study numerically investigated two variable valve actuation (VVA) strategies – early intake valve closing (EIVC) and second exhaust valve re-opening (2EVO) with a large bore marine engine operating under natural-gas/diesel RCCI mode. A fully calibrated and validated 1D engine model was utilized for VVA simulation via commercial software, GT-Power. In order to capture RCCI combus-tion behaviour on VVA, a physic-based chemical kinetic multizone model (UVATZ) was directly coupled with GT-Power. The simulation results revealed that EIVC and 2EVO could control combustion phase and extend load range to some extent by controlling in-cylinder thermal condition right before the com-bustion initiates. EIVC retards combustion phase by decreasing compression temperature while 2EVO advances combustion onset by increasing in-cylinder temperature by trapping hot residual gases.
