Non-Equilibrium behavior of dissociated hydrogen in historic Nuclear thermal propulsion reactors

Abstract

Hydrogen gas dissociation in Nuclear Thermal Propulsion (NTP) analyses and models is often assumed universally at chemical equilibrium or neglected entirely. This study examines the non-equilibrium chemical kinetics of high-speed dissociating hydrogen within a range of reactor temperature profiles using historic NTP engine inlet and outlet conditions. Below 1600 K, all reactors should be modeled at equilibrium unless somehow disrupted off the equilibrium concentration where it must be modeled in non-equilibrium. Above 1600 K, NTP systems should assume non-equilibrium behavior to accurately represent high-speed flow. However, analysis of historic NTP reactors all achieved equilibrium, modeled at the highest possible flow speeds, at the reactor outlet. Historic atomic hydrogen molar fractions at the outlet were less than 0.5%. These findings and analyses provide useful and validated assumptions for all NTP reactors for dissociation aiding future CFD analysis.