Spark anemometry applied through secondary current measurements in an optical spark ignition engine

As a technology, internal combustion engines feature high level of maturity. Nonetheless, there is still room for improvement, especially in terms of solutions that do not require significant changes to hardware components. The present work developed a method for evaluating in-cylinder fluid velocity around the spark plug based on measurements of secondary current intensity. This information can be used for reducing cycle-to-cycle variability and indirectly to increase fuel conversion efficiency. Compared to existing techniques that employ secondary voltage signals, the new procedure can be readily applied in spark ignition (SI) engines with standard ignition coil and plug. In a first phase calibration was performed on a dedicated flow rig with known fluid velocity around the spark plug. The new method was then tested on an optically accessible SI engine. Offset effects were minimized by performing relative spark duration measurements. More to the point, the discharge interval recorded during the working cycle was referenced to spark duration values recorded in quiescent conditions; this procedure can be applied on existing ignition systems without any changes in hardware. Imaging data ensured additional information on flow orientation during ignition. The results were compared to the voltage rise anemometry technique and were found to be in good agreement. Values were also directly comparable to tumble and turbulence intensity predicted by 0D/1D simulations.