20056510 (JSAE) 2005-32-0093(SAE) SETC 2005 1／12 Effects of relative port orientation on the in-cylinder flow patterns in a small unit displacement HSDI Diesel Engine Giuseppe CANTORE, Stefano FONTANESI, Vincenzo GAGLIARDI, Simone MALAGUTI Università di Modena e Reggio Emilia- Italy Copyright © 2005 Society of Automotive Engineers of Japan, Inc. and Copyright © 2005 SAE International The paper aims at providing information about the in-cylinder flow structure and its evolution of a high speed direct injection (HSDI) four valve per cylinder engine for off-highway applications. Fully transient CFD analyses by means of state-of-the-art tools and methodologies are carried out for the whole intake and compression strokes, in order to evaluate port effects on both engine permability and in-cylinder flow field evolution. Organized mean motions (i.e., swirl, tumble and squish) are investigated, trying to establish general rules in the port design optimization process, addressing relationships between the relative port orientation and the in-cylinder flow structure. Different port configurations are compared, each deriving from the rotation of the BASE port configuration on two different planes, the former being perpendicular to the cylinder axis, while the latter being parallel to the cylinder axis. Relative intake port orientation proves to strongly influence the flow field evolution within the combustion chamber, and is therefore expected to play a non negligible role on the subsequent spray evolution and fuel combustion. Keywords: Port orientation, Swirl motion, permeability, 4-valve engines, CFD 1. INTRODUCTION In – cylinder flow patterns evolution is well known to strongly influence both engine performances and pollutant emissions, by playing a fundamental role on mixture formation, early ignition development stages, mixing-controlled combustion and late-combustion fuel consumption [1, 2, 3, 4]. The ability to optimize in-cylinder flow patterns is therefore a key controlling mechanism to match the strict regulations about vehicle emissions, particularly in small unit-displacement direct injection compression ignition engines, where the air motion is important to properly stir fuel and oxidizer, since both time and space available to the fuel for vaporizing, mixing, igniting and fully burning is very limited [5, 6]. In – cylinder mean flow motion is usually addressed by means of the intensity and length in time of two main organized flow structures: the swirl vortex and the tumble vortex. The combination of these two eddies allows the designers to characterize the combustion chamber flow field by means of two average quantities, and to evaluate the effectiveness of the port design effectiveness in delaying the energy cascade from the mean flow to the small dissipative eddies. The experimental characterization of the in-cylinder flow patterns during actual engine operations, as well as their interaction with the injected fuel sprays, is far from being feasible from an engineering point of view. On one side, automotive industries usually estimate the air motion through intake valves by means of steady state flow rigs, evaluating the attitude to promote swirl and tumble vortices by means of proper steady state coefficients. Nevertheless, comparisons between fully transient and steady state evaluation of the swirl coefficient suggest a critical remark on the use of the steady flow rig for the evaluation of the swirl intensity. In fact, swirl coefficient sometimes differs significantly for a steady state and a transient analysis, not only in terms of absolute values, but also in terms of relative trend between different geometries. On the other side, mixing and combustion effectiveness are evaluated only at the engine bench, by means of time and money-costing engine prototypes, thus strongly limiting the number of tests. As a consequence, Computational Fluid Dynamics analyses of the whole intake, compression and power strokes become an unavoidable tool to optimize the air motion patterns and intensity and the air-spray interaction, allowing the designers to quickly test different engine configurations, and to gain a better insight of the multiple phenomena involved [7, 8, 9, 10, 11]. The need for accurate and cost-effective design tools is becoming even more stringent because of the growth in popularity of four valves per cylinder engines, nowadays common practice in high-speed direct-injected Diesel engines [12, 13, 14, 15]. The four valves per cylinder implies a larger complexity in determining the optimal in – cylinder flow motion, being the in-cylinder flow patterns influenced not only by the shape of each single intake port and valve, but also by the mutual interaction of the two intake streams.