Carbon-Monoxide Laser Absorption Spectroscopy Measurements over Ablating Graphite in a Shock Tunnel

Abstract

Measurements of carbon monoxide (CO) during air–carbon ablation of graphite are performed in the Sandia Hypersonic Shock Tunnel. Resistive heating is used to bring graphite samples to wall temperatures ([Formula: see text]) as measured by an imaging pyrometer. The heated models are subjected to a flow condition of [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. Tunable diode laser absorption spectroscopy measures CO temperature and concentration within the boundary layer at 50 kHz. Ablation product concentrations from experiments are presented as a function of time, including the transient startup of the tunnel. The measured CO concentration increases by approximately a factor of 2 as surface temperatures increase from 1250 to 1630 K. Finally, the CO concentration is observed to be lower than that predicted by several air–carbon ablation models, with the best agreement occurring at the higher surface temperature.