Numerical and experimental investigation on combustion characteristics of a spark ignition engine with an early intake valve closing load control Federico Millo a,⇑ , Sabino Luisi a , Fabio Borean b , Andrea Stroppiana b a Energy Department, Politecnico di Torino, c.so Duca degli Abruzzi, 24, 10129 Torino, Italy b Fiat Research Center, Strada Torino, 50, 10043 Orbassano, Italy highlights  A new intake port for a turbocharged spark ignition engine was designed and tested.  The new port promotes turbulence by increasing the tumble motion at low valve lifts.  Target of enhancing poor turbulence levels typical of EIVC at part load was reached.  Full load performance targets were not reached due to the slower combustion.  Combustion characteristics were related to in cylinder flow characteristics. article info Article history: Received 11 November 2013 Received in revised form 15 December 2013 Accepted 16 December 2013 Available online 31 December 2013 Keywords: Spark ignition engines Variable valve actuation Early intake valve closing abstract In this paper a new intake port configuration has been designed, analyzed by means of 3D CFD simulation and experimentally tested on a turbocharged Spark Ignition (SI) engine, with the aim of addressing the issue of the poor in-cylinder turbulence levels which are typical of the Early-Intake-Valve-Closing (EIVC) strategies adopted in Variable Valve Actuation (VVA) systems at part load to reduce pumping losses. The proposed intake port layout promotes turbulence by increasing the tumble motion at low valve lifts in order to achieve a proper flame propagation speed at part load. The new layout was proved to have a sig- nificant and positive effect in improving the EGR tolerance and in shortening the combustion process, especially at the lower loads, which are the more critical for VVA systems using an EIVC strategy. However, under full load operating conditions the new design (which enhances the tumble motion at the low valve lifts used at part load, but decreases the tumble intensity under the full lift operation used at full load) did not reach the performance targets, since the knock mitigation was not sufficient to com- pensate for the loss in combustion efficiency due to the slower combustion. The proposed solution could therefore be exploited only if a reduction of the engine full load performance is allowed in view of the significant benefits during part load operation. Finally, the calculated in cylinder flow characteristics were related to the experimental combustion durations, identifying, on a quantitative basis, the relationship between the turbulent kinetic energy and the burning process durations, and thus providing guidelines for further possible modifications of the engine geometry aimed to achieve a suitable combustion speed over the whole engine operating map. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction A major challenge for combustion scientists and engine devel- opment engineers is to optimize engine combustion for improved fuel economy and reduced exhaust emissions while maintaining outstanding performance, durability, and reliability at an afford- able price [1,2]. Spark Ignition (S.I.) engines have been gaining an increasing interest in the last years, especially in combination with downsizing and turbocharging, due to their noteworthy potential for fuel consumption and emissions reduction. Fuel consumption and therefore CO 2 emissions are being reduced by means of engine downsizing, which allows a shift of load points towards more efficient zones of the engine map, while performance are being preserved or even enhanced despite the smaller displacement thanks to high boost levels [3–5]. However, downsizing and turbocharging are not the only means to improve SI engine efficiency: technologies which can allow 0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.12.047 ⇑ Corresponding author. Tel.: +39 0110904517; fax: +39 0110904599. E-mail addresses: federico.millo@polito.it (F. Millo), sabino.luisi@polito.it (S. Luisi), fabio.borean@crf.it (F. Borean), andrea.stroppiana@crf.it (A. Stroppiana). Fuel 121 (2014) 298–310 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel