Flame Structure of Ammonium-Dinitramide-Based Liquid Propellant in a Small Thruster

摘要

In this paper,the flame structure of a liquid propellant ammonium dinitramide-methanol aqueous solution in asmall model thruster is investigated. The thruster is composed of an injector and a combustion chamber (including acatalyst bed) with optical windows,through which the combustion process in the atmosphere is inspected,and thetemperature distribution along the flame is measured by the tunable diode laser absorption spectroscopy method.Obvious fluctuations in temperature and flickering yellowish flame downstream of the combustion chamber areobserved,indicating that the combustion is not stable. The mean temperature distribution has a significant peakwhere a yellowish flame appears. To explain the experimental observations,a detailed gas-phase ammoniumdinitramide-methanol reaction model is used to establish the flame structure of an ideal liquid propellant,which canbe divided into several different regions,including the liquid phase,aerosol zone,and twoflame zones. Thedecomposition of ammonium dinitramide and the evaporation of methanol take place in the liquid phase and aerosolzone,whereas the gas phase reactions of methanol and the decomposition products of ammonium dmitramide takeplace in the twoflame zones. Based on the proposed theory of flame structure,it is seen that,in our experiment,thephysical and chemical processes in the liquid phase and aerosol zone are completed upstream of the catalyst bed,andthe unstable yellowish flame appearing in the combustion chamber is caused by competitive influence between the twoflame zones.