Abstract
Engine knock has become the prime barrier to significantly improve power density and efficiency of the engines. To further look into the essence of the abnormal combustion, this work studies the working processes of normal combustion and knock combustion under practical engine operating conditions using a three-dimensional computation fluid dynamics (CFD) fluid software CONVERGE (Version 2.3.0, Convergent Science, Inc., Madison, USA). The results show that the tumble in the cylinder is gradually formed with the increase of the valve lift, enhances in the compression stroke and finally is broken due to the extrusion of the piston. The fuel droplets gradually evaporate and move to the intake side under the turbulent and high temperature in the cylinder. During the normal combustion process, the flame propagates faster on the intake side and it facilitates mixture in cylinder combustion. During the knock combustion simulation, the hotspots near the exhaust valve are observed, and the propagating detonation wave caused by multiple hotspots auto-ignition indicates significant effects on knock intensity of in-cylinder pressure.
Highlights
High boost and fuel direct injection possess the potential of enhancing power density and fuel economy in downsized spark ignition (SI) engines running under high load conditions
High loads induce more harsh thermodynamic conditions in the cylinder, which promote the occurrence of the typical abnormal combustion phenomena such as the conventional knock even super-knock [1,2]
Due to the above mentioned motivations, this study investigated the end-gas autoignition in a production engine adopting 3D numerical simulation coupled with the detailed chemical mechanism of the combustion of engines
Summary
High boost and fuel direct injection possess the potential of enhancing power density and fuel economy in downsized spark ignition (SI) engines running under high load conditions. The development of high boost and direct injection in gasoline engines under low engine speed and high load operating conditions, has been threatened by the occurrence of a new abnormal combustion, namely super-knock or deto-knock [5,6]. Mittal et al [8] studied the influencing factors of the starting point of the knock from a single-cylinder gasoline engine.
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