Pre-lift Valve Actuation Strategy for the Performance Improvement of a DISI VVA Turbocharged Engine

Modern internal combustion engines (ICEs) are becoming more and more complex in order to achieve not only better power and torque performance, but also to respect the pollutant emissions and the fuel consumption (CO 2 ) limits. The turbocharger, advanced valve actuation systems (VVA) and the EGR circuit allow the ICE's load control together with the traditional throttle valve and spark advance. Thus, an higher number of operating parameters are available for the calibration engineer to achieve the required performance target (minimum fuel consumption at part load, maximum power and torque at full load, etc.). On the other hand, the increased degrees of freedom may frustrate the potentialities of so complex systems because of the effort needed to identify the optimal engine control strategies. The development of proper numerical models may assist and direct the experimental activity in order to reduce the related times and costs. Although VVA solutions could bring a reduction in the specific fuel consumption thanks to an important de-throttling of the intake system, unfortunately they can simultaneously lead to higher noise levels radiated by the intake mouth. In fact, in this case, the pressure waves travelling through the intake ducts are not properly damped by the throttle valve. In this paper a numerical methodology is developed to define the engine calibration and the intake valve lift profile that simultaneously minimize the BSFC and the noise at part load. The engine object of the study is a turbocharged Spark-Ignition Direct Injection (SIDI) ICE equipped by a lost motion valve actuation system for the intake valves. In this study, the commercial 1D thermo fluid-dynamic code GT-PowerTM is provided with user routines for the description of the combustion process and the handing of variable valve lift profiles. The engine model is thus integrated with a commercial optimization code (modeFRONTIERTM) to identify the optimized load control strategies to achieve the set objectives. The proposed methodology is also used for the definition of unconventional valve lift profiles. Particularly, the advantages related to the use of a small pre-lift before the main valve lift profile are estimated compared to a conventional EIVC strategy.