Probing Spark Discharge Behavior in High-speed Cross-flows through Modeling and Experimentation

This paper presents a combined numerical and experimental investigation of the characteristics of spark discharge in a spark-ignition engine. The main objective of this work is to gain insights into the spark discharge process and early flame kernel development. Experiments were conducted in an inert medium within an optically accessible constant-volume combustion vessel. The cross-flow motion in the vessel was generated using a previously developed shrouded fan. Numerical modeling was based on an existing discharge model in the literature developed by Kim and Anderson. However, this model is applicable to a limited range of gas pressures and flow fields. Therefore, the original model was evaluated and improved to predict the behavior of spark discharge at pressurized conditions up to 45 bar and high-speed cross-flows up to 32 m/s. To accomplish this goal, a parametric study on the spark channel resistance was conducted. Then, the parameters that best fit the experimental data were obtained using the least-squares fit technique. Results show that the model captured the spark discharge characteristics including the occurrence of the spark blowouts and re-strikes that were observed experimentally. It was also shown that the voltage and current waveforms of the spark discharge are correlated to the flow velocity across the spark plug gap. Further investigations were also performed to study the stretching rate of the spark channel under high-speed cross-flows.