INTRODUCTION The development of current internal combustion engines (ICEs) has to comply with several simultaneous requirements. On one hand, in fact, customers are becoming increasingly sensitive to fuel consumption levels, mainly because of the uprising fuel costs; on the other hand, car manufacturers are requested not to reduce, or even to increase, power/torque performance, in order to guarantee the desired level of drivability and fun-to-drive. Furthermore, both tasks have to comply with increasingly stringent pollutants emission limitations. To fulfll the above listed - often conficting - issues, ICE architecture is becoming more and more complex and new engine concepts are under continuous investigation and development [1]. Concerning spark ignition (SI) ICEs, advanced technical solutions, involving the combination of a fully fexible actuation system of the intake valves (Variable Valve Actuation - VVA), a turbocharging system and gasoline direct injection are under continuous research and development [2,3]. Particularly, a VVA system allows the designers to combine a fne tuning of the pressure waves in the intake system at full load (maximum cylinder flling) and a fexible load control without throttling the intake system (thus reducing fuel consumption). On one hand, the use of either a turbocharging or a supercharging system allows for a further reduction of the brake specifc fuel consumption at low- and medium-loads through the reduction of engine displacement (downsizing), while preserving (or even increasing) peak engine torque at high load / low engine speed and peak engine power at high load / high engine speed. On the other hand, the consequent higher pressure and temperature levels reached in the cylinders contribute to increase the engine knock tendency. Analysis of Knock Tendency in a Small VVA Turbocharged Engine Based on Integrated 1D-3D Simulations and Auto-Regressive Technique Stefano Fontanesi and Elena Severi Università degli Studi di Modena Daniela Siano Istituto Motori CNR Fabio Bozza and Vincenzo De Bellis Università di Napoli Federico II ABSTRACT In the present paper, two different methodologies are adopted and critically integrated to analyze the knock behavior of a last generation small size spark ignition (SI) turbocharged VVA engine. Particularly, two full load operating points are selected, exhibiting relevant differences in terms of knock proximity. On one side, a knock investigation is carried out by means of an Auto-Regressive technique (AR model) to process experimental in-cylinder pressure signals. This mathematical procedure is used to estimate the statistical distribution of knocking cycles and provide a validation of the following 1D-3D knock investigations. On the other side, an integrated numerical approach is set up, based on the synergic use of 1D and 3D simulation tools. The 1D engine model is developed within the commercial software GT-Power ™ . It is used to provide time-varying boundary conditions (BCs) for the 3D code, Star-CD™. Particularly, information between the two simulation tools are at frst exchanged under motored conditions to tune an “in-house developed” turbulence sub-model included in the 1D software. 1D results are then validated against the experimental data under fred full load operations, by employing a further “in-house developed” combustion sub-model. BCs are fnally passed back to the 3D code to carry out a detailed knock analysis for two full load points, namely 2100 and 4000 rpm. In particular, the knock intensity is predicted, for experimentally actuated and earlier spark advances, and the results are qualitatively compared to the AR model outcomes. CITATION: Fontanesi, S., Severi, E., Siano, D., Bozza, F. et al., "Analysis of Knock Tendency in a Small VVA Turbocharged Engine Based on Integrated 1D-3D Simulations and Auto-Regressive Technique," SAE Int. J. Engines 7(1):2014, doi:10.4271/2014-01-1065. 2014-01-1065 Published 04/01/2014 Copyright © 2014 SAE International doi:10.4271/2014-01-1065 saeeng.saejournals.org 72