Impact of Plasma Stretch on Spark Energy Release Rate under Flow Conditions 2022-01-0438

Performance of the ignition system becomes more important than ever, because of the extensively used EGR in modern spark-ignition engines. Future lean burn SI and SACI combustion modes demand even stronger ignition capability for robust ignition control. For spark-based ignition systems, extensive research has been carried out to investigate the discharge characteristics of the ignition process, including discharge current amplitude, discharge duration, spark energy, and plasma stretching. The correlation between the spark stretch and the discharge energy, as well as the impact of discharge current level on this correlation, are important with respect to both ignition performance, and ignition system design. In this paper, a constant volume combustion chamber is applied to study the impact of plasma stretch on the spark energy release process with cross-flow speed from 0 m/s up to 70 m/s. Research results show that cross-flow can significantly enhance total discharge energy as compared with under quiescent conditions. The resistance of the plasma channel increases with extended plasma length, consequently, the spark voltage and power increase, resulting in higher spark energy. The spark energy increases almost linearly with the gas flow velocity up to 20 m/s. Beyond this velocity range, a further increase in the cross-flow velocity results in a negligible increase in the spark energy. The trend is observed under three different discharge current levels, 60 mA, 400 mA, and 600 mA. Once the flow velocity increases to a certain level, where the spark energy is no longer sensitive to the change in velocity, a higher discharge current is needed to further increase the spark energy.