Study on Water Vapor Distribution in Supersonic Flow Using Tunable Diode Laser Absorption Spectroscopy

Abstract

The scramjet engine is attracting research interest due to its potential as a new propulsion system to space. Clarifying the combustion phenomena in scramjet engines is necessary for the development of the engine. This study primarily aimed to obtain water vapor distribution using tunable diode laser absorption spectroscopy (TDLAS) in a cross section of a supersonic flow containing combustion products. The supersonic wind tunnel with a vitiation air heater in the Kakuda Space Center was used to ensure that TDLAS was applied to the supersonic flow, which contained reacted gases, after the calibration using a McKenna burner. The results of TDLAS were compared with those of gas sampling to evaluate the accuracy of TDLAS measurements. The average concentrations calculated from each distribution of TDLAS and gas sampling were 1.64 mol/m³ and 2.0 mol/m³, respectively, indicating an approximately 19% of error in TDLAS measurement. As a result, TDLAS is not a suitable quantitative measurement method. However, the position of the maximum concentration of TDLAS measurement was almost the same as that of gas sampling. Therefore, it was concluded that the concentration distribution measurement in supersonic reacted flow using TDLAS can be used as a qualitative evaluation tool.