Spark Anemometry of Bulk Gas Velocity at the Plug Gap of a Firing Engine

The objective of the present work was to investigate a rapid method of obtaining the convection velocity of the bulk gas near the spark plug gap of a firing engine at the time of ignition. To accomplish this, a simple model was developed which utilized both the secondary current and voltage signals, from a conventional spark discharge. The model assumed the spark path was elongated in a rectangular U-shape by the flow. Based on experimentally measured electrical signals the mean convection velocity was computed. The convection velocity calculated by the model first needed calibration which was accomplished with a bench test that used a hot wire anemometer. The technique has a weak correlation at low velocities of 1-2 m/s, but correlates well at higher velocities up to 15 m/s. Although the accuracy of prediction by the technique is moderate, it is shown to be suitable for rapidly studying the bulk flow velocity near the plug gap in an operating engine without modification of the combustion system. It is also shown to favorably compare with data taken with a fiber optic equipped spark plug.