Numerical Simulation of Knock Combustion in a Downsizing Turbocharged Gasoline Direct Injection Engine

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.

Impact of Exhaust Gas Recirculation on Gaseous Emissions of Turbocharged Spark-Ignition Engines

“…The need to increase the intake pressure to bring in exhaust gases along with fresh air is reflected in more open throttle positions and reduced pumping losses during throttled operation. In addition, using EGR allows better combustion phasing at higher loads, which is typically limited due to knock combustion phenomena [21]. Thanks the lower reactivity of the mixture knock probability is reduced, so the spark control can be optimized, thus achieving better efficiencies [22].…”