Effects of Probe Dimensions on the Ion Density Measurements in Combustion Gas Flows

Abstract

The effects of various parameters on the ion currents to Langmuir-type cylindrical probes of Pt or Pt/Rh alloy were studied experimentally. First of all, in very low ion density flows of pure combustion gases, the effects of the potential and the dimensions of the probe on the ion current were examined. In the case, an apparent increase in ion current due to thermal emission of electrons occurred when the surface temperature of a probe containing Rh became higher than 1 900°K. The sheath thickness around a probe seemed to be larger than 0.5 mm. Furthermore, experiments were conducted in combustion gas flows, the ion densities of which were increased with the addition of potassium. Besides the effects of the potential and the dimensions of the probe, those of the flow velocity and the ion density of the gas on the ion current were examined, and an empirical equation for the ion current was obtained.