Multispecies Midinfrared Absorption Measurements in a Hydrocarbon-Fueled Scramjet Combustor

Abstract

Spatially resolved laser absorption measurements of CO, , and within an ethylene-fueled direct-connect model scramjet combustor are presented. The sensors employ a variety of laser sources at midinfrared wavelengths to provide access to fundamental vibrational band absorption transitions for each species. Both scanned-wavelength-modulation spectroscopy and scanned-wavelength direct-absorption are used, with particular attention paid to employing these methods in a manner that accounts for expected nonuniformities in temperature and composition throughout the combustor. Results for product temperatures and column densities offer insight on the ongoing combustion process downstream of fuel injection throughout the combustion-product plume, and on the significant temporal variations in the combustor. Additional tests measure the temperature and concentration of in the cavity flameholder during a flame extinction event, which gives an upper bound of the cavity residence time. These measurements are the first use of these midinfrared wavelengths for measurements in a scramjet combustor, and this work introduces an important new tool for characterizing hydrocarbon combustion in scramjet engines.