Performance optimization of a spark-ignition turbocharged VVA engine under knock limited operation

A very effective approach to improve the performance of spark-ignition internal combustion engines is the downsizing. The above technique may cause substantial BSFC detrainments at high load because of the onset of knocking combustions. In the present work, a turbocharged spark ignition engine equipped with a fully flexible valve system is numerically investigated by a 1D model. In a first stage, the engine model is validated against experimental data under both high and part load operations, in terms of overall performance and combustion evolution. The validated model is then integrated in a multipurpose optimizer with the aim to identify the engine calibrations that maximize the load and minimize the BSFC under high load knock-limited operations at a speed of 3000 rpm. The adopted optimization process shows the capability to reproduce the experimentally-identified calibration with satisfactory accuracy. In addition, the results underline the BSFC advantages related to an early intake valve closure strategy with respect to a Full Lift one, due to a better combustion phasing and a reduced mixture over-fuelling. The developed automatic procedure allows for a “virtual” engine calibration on a completely theoretical basis and proves to be very helpful in reducing the engine development costs and time-to-market.