Some measurements of the infrared spectral radiances and emissivities of hydrogen fluoride in combustion gases at 1000°C

Abstract

Spectral radiances and emissivities were determined from moderate-resolution emission and absorption measurements in the exhaust gases of a small rocket motor. Data was obtained in the 2 to 3 p region for ClFa-NHs combustion products in which hydrogen fluoride was the principal infrared emitting species. The results are presented as average spectral emissivities, which are considered to be representative of 3.0 cm-atm of HF at 1250°K. The experimental techniques and methods of data analysis are discussed in some detail. SPECTRAL emissivities in the infrared vibration-rotation bands of combustion gases arerequired for a number of engineering purposes, such as calculations of radiant heat transfer and studies of combustion dynamics in propulsion devices. The combustion products of most importance in this regard are COz, HzO, and HF. Although the infrared spectra of these molecules have been known for a great many years, only recently has attention been given to the determination of quantitative spectral emissive properties, especially at elevated temperatures. Carbon dioxide has received most of this attention; measurements of spectral emissivity in the 2.7 and 4.3 ~1 bands have been made in a furnace-heated cell,(@J) a shock tube,@) and a small rocket motor.@) The resultant data, representative of a wide range of optical depths, can be well correlated by use of a statistical band model@) and are in reasonable agreement with approximate theoretical calculations.@) similar measurements of spectral emissivity have been made and correlations are being sought for the 2.7 band of water vapor at elevated temperatures.('JQJ@ On the other hand, except for a recent determination of total emissivity in an ammoniafluorine flame(ll), no high-temperature experimental data for hydrogen fluoride have been reported in the literature.The present work consists of a set of emission and absorption measurements obtained at moderate resolution in the combustion products of liquid ammonia and chlorine trifluoride, a mixture of HF, HCI, and Nz, at a temperature of about 1250°K. Spectral radiances and emissivities were obtained at spectral slit widths of 0.005 and 0.02 p in the 2 to 3 p and the 2 to 5 p regions respectively. * The experimental measurements reported herein were performed at Rocketdyne, a division of