Measurements of NH3 in a Shock Tube for Investigating the Chemical Kinetics of Rocket Propellants

Ammonia (NH3) is a promising alternative carbon-free fuel and an important intermediate and final species of nitrogen-based propellants. For these reasons and others, significant research is directed towards studying NH3 especially pertaining to its chemical kinetics. Until recently, NH3 was never measured using laser absorption spectroscopy to study its chemical kinetics. This recent NH3 measurement was conducted by the authors’ group using a newly developed laser absorption diagnostic that probes the v2 fundamental band of NH3 in the mid-infrared near 10.4 µm. The present study utilized this recently developed NH3 diagnostic to highlight its capabilities and potential future use for studying propellant-related combustion chemistry. The laser was operated using two methods: a scanned-wavelength method to measure the absorption spectra of NH3-containing mixtures, and a fixed-wavelength method to measure NH3 time histories behind reflected shock waves. The scanned-wavelength method was used to determine the NH3 mole fraction in multi-component gas mixtures; such a method presents future promise when the accurate determination of NH3 in a sampled gas is needed. The fixed-wavelength method, coupled with a shock tube, was used to follow NH3 time histories during the oxidation of NH3/O2 in Ar; such method shows promise for studying the chemical kinetics of ammonia, especially that pertained to nitrogen-based propellants.