Spark ignited internal combustion engine system, engine control method and computer program product for engine control

There is provided, in one aspect of the present description, an internal combustion engine system. In one example, the system comprises a controller configured to control an intake valve closing timing varying mechanism to vary a closing timing of the intake valve to regulate air charged in a combustion chamber in accordance with engine operating conditions and, in a first engine operating condition where a least volume of air is required to be charged into the combustion chamber, retard a closing timing of the intake valve to a most retarded crank angle which is after bottom dead center during a cylinder cycle and satisfies the following formulas: ± >= - 0.2685 x µ0 2 + 10.723 x µ0 + 15.815 and µ0 >= 11.0, where ± is the most retarded crank angle and µ0 is a geometric compression ratio of the engine.