A new measuring technique of gas stream velocity has been developed, based on the phenomenon that the path of an electric discharge moves downstream under the influence of the gas stream. A probe (a thin conductive wire grounded by a resistance) is placed at a fixed distance downstream from the electrodes. When the discharge path arrives at the probe, the probe voltage rises rapidly. By means of measuring the time interval elapsing between the beginning of the spark and the rising of probe voltage, the stream velocity can be determined by the formula, U = Kℓ/τ, where K is a constant. As the result of preliminary tests, it was confirmed that the constant K is independent of distance ℓ, intensity of turbulence, temperature, and pressure of flowing gases, and depends only on the electrode spacing. The digital measurement of the time interval can be made easily. This technique can be applied not only to a steady flow but also to a pulsating flow such as that in the inlet and exhaust pipe or the air flow in the cylinder of the internal combustion engine.
In this paper, the details of the measuring technique and some results obtained by applying this technique to the inlet flow, exhaust flow, and air flow in the cylinder of two-stroke cycle spark-ignition engines are described.