Numerical Investigation of the Spark Plug Orientation Effects on Flame Kernel Growth 2019-01-0005

Spark plug design is critical for the performance of spark ignited (SI) engines, however, its orientation is frequently not controlled for most of production engines, which has great impacts on ignition and subsequent flame propagation processes. In the present work, a recently developed comprehensive ignition system model--the VTF ignition model, has been employed to investigate the effects of spark plug orientation on ignition and flame kernel growth. Three orientations for the spark plug, including downstream, crossflow, and upstream relative to the flow, have been considered under a typical a high-speed high-load condition in a GDI engine. Electrical circuitry model was validated by comparing the simulation results with measured secondary current and secondary voltage with good agreement. Engine simulation results show that different spark plug orientations have different velocity distributions near the spark plug, which consequently influences arc growth including arc length, arc location and energy deposition due to its interaction with local gas flow field. In particular, it is found that the ground strap blocks the tumble flow and generates a recirculation zone behind in the upstream configuration, which substantially limits the arc and flame kernel growth. Meanwhile, these orientation differences can also result in different contact surface area with the solid structure that enhances heat loss and facilitates flame quenching, both of which will slow down flame kernel growth. This work provides useful guidance on general spark-ignition modeling and emphasizes the significance of spark plug orientation in engine design and calibration.