Infrared laser absorption sensors for multiple performance parameters in a detonation

Laser absorption sensors for temperature and H2O near 1.4 and 2.5 mu m, CO2 near 2.7 mu m, and CO near 4.8 mu m were developed, validated, and deployed in an ethylene-fueled pulse-detonation combustor (PDC). Each sensor was fiber-coupled to enable remote light delivery to the PDC and photo-voltaic detectors were mounted directly to the PDC for improved light collection. Measurements were acquired simultaneously along two orthogonal lines-of-sight (LOS) in both the PDC combustion chamber and the throat of a converging-diverging nozzle located at the PDC exit. Measurements in the nozzle throat were combined with a choked-flow assumption to calculate the time-resolved enthalpy flow rate exiting the PDC. All sensors used first-harmonic-normalized wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f/ 1f) to account for non-absorbing transmission losses and emission. Furthermore, strong mid-infrared absorption transitions were used to enable improved measurement accuracy and precision. These sensors were validated in non-reactive shock-tube experiments at temperatures and pressures up to 2700 K and 50 atm. There, these sensors exhibited a nominal accuracy of 3 to 5% with bandwidths from 2 to 20 kHz. Measurements in the PDC indicated peak temperatures near 3500 K with near-stoichiometric proportions of H2O and incomplete conversion of CO to CO2. The stagnation enthalpy flow rate was highly transient, but repeatable with peak flow rates near 25 MW. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.