In four-stroke S.I. engines, direct injection allows reducing fresh charge temperature (fuel evaporation heat is subtracted from air, not from inlet valves and ducts), with benefits for volumetric efficiency, combustion efficiency and knocking resistance that allows higher compression ratios [1-3]. As a result, engine power and fuel economy increase. If direct injection is associated with charge stratification, further benefits in fuel economy occur at partial loads, due to lower combustion temperatures, unthrottled operation and smaller heat flow to combustion chamber walls [4]. However, direct injection is justified only if it leads to significant improvements in engine performance compared to the most performing indirect injection systems. This explains the progress of the direct injection & charge stratification technique from wall-guided to purely air-guided spray, up to the most recent technique consisting in self-guided spray by outward-opening injectors. This last solution reduces flow field constraints and renders stratification less sensitive to engine operating conditions changes. As well, these injectors give significant benefits in homogeneous-charge operation especially when dealing with high-performance engines, since they improve charge micro-homogeneity and fuel distribution at high engine speeds. This occurs somewhat independently from any particular flow field feature and combustion chamber shape. In consequence, more freedom is allowed in combustion chamber design that can be better aimed at achieving high thermal and volumetric efficiency and as well permits simple and hence light pistons, required by high-performance engines with high mean piston speeds. Accordingly, a numerical study has been conducted, aimed at verifying the feasibility and at predicting the benefits of direct injection by outward-opening injectors, in the case of Lamborghini V12 engine, presently equipped with an indirect injection system. Till now, the study has only considered homogeneous-charge operation. Computational Fluid Dynamics (CFD) 3-D predictions are reported in the paper and comparisons are given between the outcomes of the original indirect injection and the ones of direct injection.

CFD Study of GDI for Lamborghini V12 Engine

MUSU, ETTORE;GENTILI, ROBERTO;
2008-01-01

Abstract

In four-stroke S.I. engines, direct injection allows reducing fresh charge temperature (fuel evaporation heat is subtracted from air, not from inlet valves and ducts), with benefits for volumetric efficiency, combustion efficiency and knocking resistance that allows higher compression ratios [1-3]. As a result, engine power and fuel economy increase. If direct injection is associated with charge stratification, further benefits in fuel economy occur at partial loads, due to lower combustion temperatures, unthrottled operation and smaller heat flow to combustion chamber walls [4]. However, direct injection is justified only if it leads to significant improvements in engine performance compared to the most performing indirect injection systems. This explains the progress of the direct injection & charge stratification technique from wall-guided to purely air-guided spray, up to the most recent technique consisting in self-guided spray by outward-opening injectors. This last solution reduces flow field constraints and renders stratification less sensitive to engine operating conditions changes. As well, these injectors give significant benefits in homogeneous-charge operation especially when dealing with high-performance engines, since they improve charge micro-homogeneity and fuel distribution at high engine speeds. This occurs somewhat independently from any particular flow field feature and combustion chamber shape. In consequence, more freedom is allowed in combustion chamber design that can be better aimed at achieving high thermal and volumetric efficiency and as well permits simple and hence light pistons, required by high-performance engines with high mean piston speeds. Accordingly, a numerical study has been conducted, aimed at verifying the feasibility and at predicting the benefits of direct injection by outward-opening injectors, in the case of Lamborghini V12 engine, presently equipped with an indirect injection system. Till now, the study has only considered homogeneous-charge operation. Computational Fluid Dynamics (CFD) 3-D predictions are reported in the paper and comparisons are given between the outcomes of the original indirect injection and the ones of direct injection.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/123223
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