A Theoretical Comparison of Various VVA Systems for Performance and Emission Improvements of SI-Engines

A wide experimental investigation on a 16 valves, 1242 cm³ SI-engine is reported. Experimental data were collected in correspondence with about 250 different operating conditions of the engine. This allowed to deeply assess the accuracy of a simulation model (1Dime code), developed by the authors, based on a one-dimensional computation of the gas flow in the manifolds, and on a quasi-dimensional fractal approach for combustion simulation. The model is then employed to theoretically verify the advantages that can be exploited from the adoption of various VVT (Variable Valve Timing) or VVA (Variable Valve Actuation) systems, including those realizing a throttle-less operation of the engine. The gains predicted in terms of torque profile at WOT, and of BSFC or NO_x emissions at part load are quantified and discussed. The main objective is the development of a methodology, which can substantially reduce experimental activity and help the definition of optimal control strategies of a VVT-equipped engine.