ADVANCES IN AMMONIA COMBUSTION CHEMISTRY AND NH3 SENSING USING LASER DIAGNOSTICS

Abstract

Ammonia (NH3) is a promising alternative carbon-free fuel. For this reason and others, significant research is directed towards studying NH3 especially pertaining to its chemical kinetics. A brief review of the literature on ammonia combustion chemistry is provided in this paper, with emphasis on the studies related to fundamental reaction kinetics at elevated temperatures. 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 ammonia combustion chemistry and also as an ammonia sensor for practical applications. 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 a method shows promise for studying the chemical kinetics of ammonia.