Comparative investigation of alternative intake strategies to improve the efficiency of multivalve spark-ignition internal combustion engines

This study aims at analysing alternative intake strategies in order to improve the breathability and the fuel consumption of multivalve spark-ignition engines. To this purpose a twofold approach has been adopted based on an experimental and a numerical investigation. The experimental characterisation has been carried out at a steady flow rig in terms of discharge and flow coefficients, while a one-dimensional numerical model has been used to evaluate the engine performance in real operating conditions. The attention has been focused on low engine loads that are characterised by a noticeable decrease in the global efficiency and fuel economy. In particular, the standard intake strategy has been compared to an alternative control based on the deactivation of an intake valve and unthrottled flow. The investigation demonstrates that at low engine loads the opening of a single inlet valve (deactivation strategy) provides a positive influence on the engine performance owing to the possibility to minimise the pumping losses induced by the throttling process and to promote more organised flow structures inside the cylinder. Consequently, a significant improvement in the engine breathability and an interesting fuel saving are produced.