Simulation of knock and super-knock in spark ignition engines

Pre-ignition in spark ignition engines is a critical issue that leads to severe knocking events and can damage the engine catastrophically. It is widely accepted that pre-ignition emanates from hot spots inside the combustion chamber. The location of the hot spot is expected to influence the knock intensity that may result from the pre-ignition event. In this study, full cycle engine simulations are conducted to investigate the effects of the location of the hot spot inside the cylinder on subsequent combustion behavior. The simulations are performed using CONVERGE, a three-dimensional computational fluid dynamics (CFD) code, incorporating reduced chemistry, turbulence modeling and moving structures (valves, piston). Gasoline direct injection (GDI) spray is represented by the Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) spray breakup model with the renormalization group k-epsilon turbulence model to describe the internal flow field. A G-equation model for flame tracking coupled with a multi-zone model is utilized to capture flame propagation, auto-ignition and subsequent combustion processes. The endgas temperature is higher for pre-ignition cycles when compared to normal spark combustion cycles, which favors the endgas auto-ignition. Strong formation of CH2O, which is an indicator of cool flame, was found in the endgas region ahead of the flame front in pre-ignition cycles. A method to simulate pre-ignition cycles and techniques to analyze the pre-ignition results are proposed in the study.