COMBUSTION BEHAVIOR OF HAN-BASED LIQUID PROPELLANTS

Open Access
Author:
Chang, Yi-Ping
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 02, 2002
Committee Members:
  • Harold Harris Schobert, Committee Member
  • Fan Bill B Cheung, Committee Member
  • Kenneth K Kuo, Committee Chair
  • Stefan Thynell, Committee Member
  • Thomas Litzinger, Committee Member
Keywords:
  • pressure exponents.
  • burning rate controlling mechanisms
  • decomposition
  • autocatalytic
  • pyrolysis
  • propellants
  • hydroxylammonium nitrate
  • combustion
Abstract:
Hydroxylammonium nitrate (HAN)-based liquid propellants have many attractive features. For gun propulsion applications, they have advantages in storage, logistics, and demilitarization. For space propulsion applications, their high density, low toxicity, and low freezing point are highly desirable. In this investigation, the combustion behavior of three HAN-based liquid propellants were investigated. The first propellant studied was XM46, whose fuel component is triethanol ammonium nitrate [TEAN, (HOCH2CH2)3NHNO3,]. The flame structure displayed three different stages: (1) nearly simultaneous decomposition of both HAN and TEAN initiating in the liquid to produce gases around 300°C, (2) breakdown of heavy opaque intermediate molecules into transparent species, and (3) reaction of transparent species to form final products in the luminous flame. The pyrolysis data indicates that TEAN participates in the first-stage combustion. The second propellant was HANGLY26, with glycine as the fuel component. No luminous flame was observed in any combustion tests. The burning rate of HANGLY26 exhibited four burning rate regimes with different pressure exponents for pressures ranging from 1.5 to 18.2 MPa. The decrease of the burning rate pressure exponent with increasing pressure at 3.9 MPa was caused by the higher percentage of the gaseous products formed, which reduced the heat feedback. The increase of the burning rate pressure exponent with increasing pressure at 8.8 MPa was due to a reduction of energy requirement of water vaporization. Thus, a higher percentage of the surface heat release can be used to pyrolyze the active ingredients. The third propellant was HAN269MEO15, with methanol as its fuel component. An abrupt discontinuity of the burning rate curve was observed between 1.14 and 1.21 MPa. For tests of chamber pressures near 1.14 MPa, pulsating burning was observed. The temperature of the products after the reaction front was bounded by the boiling point of methanol and water, indicating the influence of the evaporating process of both liquids. The burning rate curves of the HAN-based liquid propellants shared features such as dome-like burning rate curves, negative slope regions, and extremely high pressure exponents. Staged combustion characteristics were commonly observed among these three propellants, which result from the autocatalytic decomposition of HAN. Based upon a simple kinetic model of HAN/fuel interaction proposed by the author, possible ways of reducing autocatalytic characteristics are suggested. They are: utilization of nitrous acid-scavenging fuel, consideration of fuels which would react more readily with NO2, and the increase of fuel percentage in the propellant formulation to slightly fuel-rich compositions.