Fuel Consumption and Pollutant Emission Optimization at Part and Full Load of a High-Performance V12 SI Engine by a 1D Model

Modern internal combustion engines show complex architectures in order to improve their performance in terms of brake torque and fuel consumption. Concerning naturally-aspirated engines, an optimization of the intake port geometry, together with the selection of a proper valve timing, allow to improve the cylinder filling and hence the performance. The identification of an optimal calibration strategy at test bench usually requires long and expensive experimental activities. Numerical tools can help to support engine calibration, especially in the early design phases. In the present work, a 12-cylinder naturally aspirated spark ignition engine is investigated. The engine is experimentally tested under full and part load operations. Main performance parameters, in-cylinder pressure cycles and raw pollutant emissions are measured. The engine is schematized in a one-dimensional model (GT-Power™), where “user routines” are employed to simulate turbulence, combustion, knock and pollutant production. 1D model is validated against the experimental data, denoting a good accuracy. A calibration procedure is implemented by an external optimizer, coupled with the 1D engine model, with the aim of minimizing the fuel consumption. The procedure decision parameters are intake and exhaust valve timings, and combustion phasing. Proper constraints are posed for residual gas fraction and knock intensity. The optimal calibration strategies have been recognized for two operating conditions, where the engine most frequently works along an RDE driving cycles. Main drivers for engine efficiency are intake de-throttling at part load, thanks to the internal EGR caused by a Miller-Atkinson valve strategy, and cylinder filling maximization at high load. A ‘virtual’ calibration of the considered engine, employing the developed automatic procedure, is identified on completely theoretical basis. The proposed methodology shows the capability to drive and support the experimental engine calibration and presents the potential to be very helpful in reducing the related costs and time-to-market.