Shock-Tube Spectroscopic CO Measurements and Kinetics Modeling of Rocket Propellants

Propellants based on Ammonium Perchlorate (AP)/Hydroxyl-Terminated PolyButadiene (HTPB) are extensively used in aerospace propulsion applications. The key features of the gas-phase combustion chemistry behavior of AP/HTPB can be represented by a surrogate mixture of ammonia (NH3), hydrocarbon (CH4), and chlorine precursors (CHCl3 or CCl4). This study aimed to understand the interactions between NH3-CH4-Cl and CH4-Cl, where the chlorine is produced via the thermal decomposition of CHCl3 and CCl4, respectively. New measurements of CO time-history profiles were performed in a shock tube using a CO laser absorption diagnostic, the P(20) transition line centered at 2059.91 cm-1. The experiments were carried out for CHCl3/CH4/NH3 and 0.1 CCl4/0.9 CH4 oxidation at an equivalence ratio (ɸ) of 1.0 in 99.5% He/Ar with temperatures ranging from 1460 to 2130 K, and near atmospheric pressure. This CO quantification is a continuation by the present authors to collect unique target data to develop and validate the detailed chemical kinetics mechanisms that are much required for understanding and modeling the AP/HTPB combustion process. While both precursors produce COCl2 via CHCl3 → CCl2 → COCl2 and CCl4 → CCl3 → COCl2, CO is then formed via the two consecutive reactions COCl2 + M ⇋ CClO + Cl + M and CClO ⇋ CO + Cl. The 0.1 CCl4/0.9 CH4 mixture was specifically designed to compel the formation of CO from Cl-related reactions, namely CH4 + Cl ⇋ CH3 + HCl and CH3 + Cl ⇋ CH2 + HCl providing the CH2 for the sequence CH2 → HCO → CO.