International Journal of Automotive Technology, Vol. 13, No. 3, pp. 389-399 (2012) DOI 10.1007/s12239-012-0036-1 Copyright © 2012 KSAE/ 064-05 pISSN 1229-9138/ eISSN 1976-3832 389 APPLICATION OF A THERMODYNAMIC MODEL WITH A COMPLEX CHEMISTRY TO A CYCLE RESOLVED KNOCK PREDICTION ON A SPARK IGNITION OPTICAL ENGINE G. D’ERRICO 1)* , T. LUCCHINI 1) , S. MEROLA 2) and C. TORNATORE 2) 1) Department of Energy, Politecnico di Milano, Milano 20156, Italy 2) Istituto Motori, CNR, Napoli 80125, Italy (Received 15 March 2011; Revised 27 August 2011; Accepted 6 September 2011) ABSTRACT-A combination of experimental and numerical methodologies is proposed for the investigation of knocking in spark ignition engines to aid in better understanding the physical and chemical processes that occur and to exploit the capabilities of a developed computational tool. The latter consists of a thermo-fluid dynamics model, which is part of an advanced 1-D fluid dynamics code for the simulation of the entire engine, and a complex chemistry model, which can be embedded into the thermo-fluid dynamics model using the same integration algorithm for the conservation equations and the reacting species. Their mutual interaction in the energy balance will be considered. The experimental activity was carried out in the combustion chamber of an optically accessible, single-cylinder P.F.I. engine equipped with a commercial head. The experimental data consisted of optical measurements correlated to the combustion and auto-ignition processes within the cylinder. The optical measurements were based on 2-D digital imaging, UV visible natural emission spectroscopy and the chemiluminescence of radical species (OH and HCO). The engine parameters, the pressure signals of the related data and optical acquisition are compared on an individual cycle basis in the simulation by running the engine at a constant speed and varying the spark advance from normal combustion to heavy knock conditions. KEY WORDS : Knock, Thermodynamic model, Complex chemistry, Optical diagnostics, Emission spectra 1. INTRODUCTION The current evolution of spark ignition engines is evidence for how this technology has high potentialities both in terms of efficiency and emissions control. The former of these two challenges has stronger key issues in the development of new engines with higher boosting and downsizing. Additionally, the extension of stoichiometric operations may also allow for a further reduction in pollutant emissions (Gerty and Heywood, 2006). Many other design variables, such as higher compression ratios, VVT techniques, direct gasoline injection and lower friction, are further contributing to the ongoing technology evolution. In such scenarios, modern engines are designed to work in many operating conditions that are very close to the knock limit in which exploitation and control become relevant challenges as well. In particular, one matter of interest is the occurrence of the auto-ignition phenomenon in the fresh gases ahead of the flame front during its normal propagation. Therefore, it is just as important to predict and investigate the temperature, pressure and composition of the mixture as it is to investigate the heat fluxes and fuel characteristics. The onset of auto-ignition is almost exclusively governed by the chemical kinetics (Heywood, 1988), but its timing strongly depends on the velocity of the propagating flame front that compresses the ending gas. To investigate this phenomenon, several numerical tools were developed by coupling computational fluid dynamics models with chemical kinetic mechanisms. The complexity and computational cost of such tools can vary greatly depending on the adopted spatial discretization and the detail of the employed kinetic mechanism. Liu (Liu and Chen, 2009) has recently reviewed the various levels of available engine models that may be used for knock prediction. A useful numerical tool to model such a complex phenomenon should be able to simulate all of the possible engine operating conditions and the effects of the fundamental engine parameters and fuel characteristics through a deep understanding of both the thermodynamic and chemical mechanisms that control the combustion process. To achieve this result, a mutual interactive coupling between a thermo-fluid dynamics model and an advanced kinetics code is required. In particular, in the present work, a detailed kinetics code including low-temperature oxidation mechanisms has been embedded into an engine simulation model based on a 1-D schematization of an intake and exhaust system and a two- *Corresponding author. e-mail: derrico@polimi.it