Experimental and Numerical Investigation of the Flow Field Effect on Arc Stretching for a J-type Spark Plug

Nowadays internal combustion engines can operate under lean combustion conditions to maximize efficiency, as long as combustion stability is guaranteed. The robustness of combustion initiation is one of the main issues of actual spark-ignition engines, especially at high level of excess-air or dilution. The enhancement of the in-cylinder global motion and local turbulence is an effective way to increase the flame velocity. During the ignition process, the excessive charge motion can hinder the spark discharge and eventually cause a misfire. In this perspective, the interaction between the igniter and the flow field is a fundamental aspect which still needs to be explored in more detail to understand how the combustion originates and develops. In this work, a combined experimental and numerical study is carried out to investigate the flow field around the spark gap, and its effect on the spark discharge evolution. Two different velocities of the flow field are explored and compared to the static configuration under ambient conditions in an air flow channel, investigating the effect of the orientation of a conventional J-type spark plug. Results of numerical simulations predict spark stretching that is in close agreement with experimental observations. The model results are used to provide insight into the spatial and temporal development of the spark discharge. This work provides a numerical tool that can be extremely useful to link the interaction between the in-cylinder charge motion and the spark discharge to the engine cycle-to-cycle variability prediction.