Numerical analysis of misfire in an automotive lean-burn direct-injection spark-ignition engine

Charge dilution strategies, such as exhaust gas recirculation and lean-burn operation, enhance internal combustion engine (ICE) efficiency and reduce NOx emissions. However, strong charge dilution can lead to cycle-to-cycle variation (CCV) and misfires. In-cylinder aerodynamics significantly influence flow evolution and mixture formation, introducing variation in governing flow variables. This study investigates flow and mixture states during ignition and their impact on flame propagation using multi-cycle Large-Eddy Simulation (LES) of an automotive lean-burn direct-injection spark-ignition (DISI) engine. Special focus is given to flow phenomena near the spark plug. Flow fields and equivalence ratios are compared across fast, slow, and misfire cycles during compression to assess differences in flow evolution and mixture formation. Key characteristics, including spark gap velocities, turbulent kinetic energy, and equivalence ratios, are analyzed at the spark plug during ignition. Analysis of the tumble flow evolution shows high tumble intensity in both propagating and misfire cycles; however, in fast cycles, a marked reduction is observed toward the end of compression. Mixture evolution indicates leaner conditions in misfire and slow cycles. At the spark plug location, misfire cycles exhibit the highest flow velocities but the lowest turbulent kinetic energies, whereas fast cycles show the inverse behavior. Spray influence on tumble formation is examined, revealing differences in spray cone characteristics and penetration. Misfire cycles exhibit slightly lower penetration depths than fired cycles. These findings provide insights into mitigating misfire in lean-burn DISI engines.