A Numerical Investigation on VVA Influence on the Combustion Phase for Premixed Combustion Engine Under Partial Load Conditions

Nowadays, the vehicle hybridization and the use of more clean fuel in heavy-duty applications brings to a new beginning in the use of spark ignition engine. In standard intake system, the pre-mixed fuel air mixture is controlled by the injection of fuel after the throttle valve. Then, intake system, consisting in intake duct, valve number and geometry and cylinder head shape influence the characteristics of the intake flow within the cylinder up to the ignition of the combustion by the spark plug. The technology advancement in fluid-power and electrical actuation gives the opportunity to decouple the intake and exhaust valve actuation with respect to the standard cam shaft distribution. The Variable Valve Actuation (VVA) concepts is not new, but its application is now affordable and flexible enough to be applied in partial load conditions. Here, by means of three-dimensional numerical simulations the intake and combustion process is studied with a finite volume approach to solve the mass, momentum and energy equations together with an Extended Coherent Flamelet Model (ECFM). Two different approaches in driving the intake valve lift profiles are studied. The engine is equipped with two symmetrical intake valves. Two strategies are studied with reference to a partial load condition: a standard lift profile for both the intake valves, and a single valve lift, keeping constant the overall mixture intake mass. The intake flow characteristic and its influence on the combustion process is studied comparing the above mentioned two strategies. Hence, the turbulence production is enhanced in single lift strategy increasing the residual turbulent kinetic energy till the spark ignition promoting the combustion velocity.