An experimental study was performed to investigate spark ignition and subsequent spark stretch evolution of inert nitrogen charge gas under high-velocity flow conditions across the electrode gap in a constant-volume optical combustion vessel. The vessel is capable of generating various in-cylinder thermodynamic conditions representative of light-duty spark ignition engines. It realizes a high flow velocity of 32 m/s created by a new high cross flow design. The characteristic behavior of the spark stretch was captured through a high-speed imaging of flow under elevated pressure conditions starting from atmosphere to 45 bar. Results show that the spark flowing downstream the spark plug is subject to restrike after electrical breakdown in high speed flows. Spark plug orientations and gap sizes as well as the charge gas pressure are determined to have significant influence on spark stretch development and electrical discharge time prediction. It was observed that wider spark plug gap leads to reducing the electric field which results in a higher breakdown voltage and shorter discharge. Shortest discharge duration occurs at the charge gas pressure of 45 bar under the flow velocity of 32 m/s while the spark plug is perpendicular to ground strap. Results also indicate that lower charge gas pressures and flow velocities lead to longer electrical discharge. The discharge at 10 m/s is 1.5 times the case in which the incoming gas flows at 32 m/s and the atmospheric pressure. It was also shown that how different electrode orientations change the ignition output due to the change of the flow direction.
Mary P. Zadeh, Henry Schmidt, William Atkinson, Jeffrey Naber