Research on in-cylinder pressure oscillation characteristic during knocking combustion in spark-ignition engine

Pressure oscillation is a typical phenomenon during knocking combustion in spark-ignition (SI) engines, and relevant study is mainly focused on low temperature chemical kinetics and optical experiments. In this paper, coupling of pressure wave equation and KIVA-3V code with reduced chemical kinetic scheme has been conducted to systematically investigate pressure oscillation characteristic during knocking cycles based on a SI engine. Simulation model has been tested by the validation of calculated results, including cylinder pressure, pressure oscillation and FFT spectral. Then visualized flame images from high speed camera and 3D CFD results have been presented, which shows that when auto-ignition occurs, pressure rise caused by violent heat release of auto-ignition reaction is much larger than that from spark-ignition flame front. This is confirmed by the discussion on contribution of various excitation resource to pressure oscillation, which indicates that end-gas auto-ignition reaction plays a dominant role in the pressure oscillation formation. Finally, effects of different levels of cooled exhaust gas recirculation (EGR) on pressure oscillation has been researched, which shows that appropriate amount of cooled EGR can effectively inhibit end-gas auto-ignition and high-frequency pressure oscillation due to the thermo-chemical properties of exhausted mixture.