Conference PaperLaser absorption of carbon dioxide at the vibrational bandhead near 4.2μm in high-pressure rocket combustion environmentsLee, Daniel D.; Bendana, Fabio A.; Nair, Anil P.; Spearrin, Raymond M.; Danczyk, Stephen A.; Hargus, William A.nullA novel laser absorption sensing strategy has been developed to evaluate combustion progress through quantitative measurements of carbon dioxide (CO2) in high-pressure (> 50 atm), high-temperature (> 3000 K) hydrocarbon-fueled rocket combustion flows. The sensor enables a broad range of operability by probing rovibrational transitions in the bandhead of CO2 near 4.2 #22;m, accessed with an interband cascade laser. Under extreme rocket conditions, this targeted bandhead region experiences line-mixing effects that favorably distort the molecular spectra. A preliminary spectroscopic model of line-mixing effects has been developed utilizing a high-enthalpy shock tube to achieve scalability of spectral simulations over a range of high temperatures and high pressures. The model is employed for quantitative interpretation of measured absorption signals. The mid-infrared light source was fiber-coupled for remote light delivery at propulsion test facilities. A wavelength modulation spectroscopy technique utilizing normalized-second harmonic detection was implemented for acquiring differential absorption signals in a harsh rocket combustor environment. Using this method, measurements of CO2 concentration have been demonstrated over a range of operating conditions up to 83 bar in a single-element-injector RP-2/GOx rocket combustor at the Air Force Research Laboratory in Edwards, CA.2020-01-0510206730AIAA SciTech Forum 2020https://doi.org/10.2514/6.2020-02981752516National Science Foundation