1990 Volume 25 Issue 8 Pages 498-504
Transient concentration of a single-shot gas jet was measured by using laser interf erometry. A He-Ne laser beam was divided by a beam splitter into test and reference beams, and interference fringes were produced by making the beams intersect after the test beam has passed through the test medium. Hydrogen gas jet was injected into the atmosphere passing through the test beam. When the density of the mixed gas of hydrogen and air changes, the optical path length of the test beam changes with a corresponding change of the refractive index, and then the interference fringes move. Two photo-transistors located in π/2 phase difference were used to detect the movement of the interference fringes by translating the luminousity into voltages.
The change in the refractive index mesured in this study indicates the change in total optical length of the laser beam. The jet is assumed to be axisymmetric. By means of the onion peeling method, the concentration distribution of the gas jet in each section was determined.
Tht penetration distance of the jet agrees with the configurations of the jet observed from schlieren photographs. The laser interf erometry is extremely useful for the measurement in the transient concentration of unsteady gas jet because this method has a high response and no intrusion into the jet. The concentration distribution from this method shows a similar result to that obtained by using a hot-wire as concentration measurement.
