EXPERIMENTAL AND NUMERICAL INVESTIGATION ON THE EFFECTS OF LOW PRESSURE COOLED EGR ON KNOCK TENDENCY AND PERFORMANCE OF A DOWNSIZED TURBOCHARGED SI ENGINE

Cooled Exhaust Gas Recirculation (EGR) is a viable technique to mitigate the knock tendency and to improve the fuel consumption of Spark-Ignition (SI) engines. This paper aims at investigating the effects of a low pressure cooled EGR system on the performance and emissions of a 2-cylinder turbocharged SI engine. In a first stage, experiments are carried out at 3000 rpm at different loads (5, 12 and 16 bar IMEP) with the external EGR circuit closed. For each point, the standard ECU calibration is applied for the spark timing, airto- fuel ratio, throttle valve opening and turbocharger setting. In a second stage, for each tested condition, the external EGR is activated, and the load is maintained adjusting the boost pressure and the spark timing. Experimental results are used to validate a 1D engine model, developed in GT-Power(TM) software, integrated with user-defined sub-models for a refined description of the in-cylinder phenomena, namely turbulence and combustion. Both numerical and experimental results highlight maximum EGR benefits over BSFC at low load, thanks to the reduction in pumping losses. At high load, lower improvements occur, mainly arising from a slight better knock resistance. The proposed approach showed the capability to explore the potentiality of the EGR technique application on SI engines, thanks to the combination of focused experimental tests and refined 1D simulations