High-bandwidth absorption-spectroscopy measurements of temperature, pressure, CO, and H2O in the annulus of a rotating detonation rocket engine

The development and application of two laser-absorption-spectroscopy diagnostics capable of performing high-bandwidth measurements of (1) temperature, pressure, and CO, and (2) temperature and H 2 O in the annular combustion chamber of a rotating detonation rocket engine (RDRE) are presented. The mid-infrared (MIR) diagnostic utilized a quantum-cascade laser (QCL) to measure absorbance spectra of three CO absorption transitions near 2008.5 cm - 1 at 750 kHz using scanned-wavelength direct absorption. Measurements of gas temperature, pressure, and CO partial pressure were obtained from the QCL diagnostic using a nonlinear fitting routine to fit simulated CO absorbance spectra to measured absorbance spectra. The near-infrared (NIR) diagnostic utilized two tunable diode lasers (TDLs) emitting near 7185.6 and 6806.0 cm - 1 which were modulated at 35 and 45.5 MHz, respectively, and scanned over the linecenters of their respective H 2 O absorption transitions to obtain measurements of WMS-4 f /2 f and WMS-2 f /1 f signals. WMS-4 f /2 f measurements were used to infer the collisional-broadening full-width at half-maximum (FWHM) of the H 2 O transitions, and the WMS-2 f /1 f signals were then used to infer the gas temperature and H 2 O partial pressure at up to 1 MHz. The diagnostics were packaged in single-ended sensor assemblies to enable measurements in the annulus of a methane–oxygen RDRE, and results are presented for a test case with the RDRE operating at an equivalence ratio of 1.15 and a total propellant mass flow rate of 0.6 lb/s.