High-bandwidth absorption-spectroscopy measurements of temperature, pressure, CO, and H$$_2$$O in the annulus of a rotating detonation rocket engine

• DOI: 10.1007/s00340-021-07703-9
• Publication Date: 2021-11-16T17:02:34Z
• Authors: Garrett C. Mathews; Matthew G. Blaisdell; Aaron I. Lemcherfi; Carson D. Slabaugh; Christopher S. Go...
• Keywords: 0103 physical sciences; 7. Clean energy; 01 natural sciences

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-4f/2f and WMS-2f/1f signals. WMS-4f/2f measurements were used to infer the collisional-broadening full-width at half-maximum (FWHM) of the H $$_2$$ O transitions, and the WMS-2f/1f 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.