experimental studies on condensed-phase interactions of hypergolic propellants

Open Access
Author:
Wang, Shiqing
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 26, 2013
Committee Members:
  • Stefan Thynell, Dissertation Advisor
  • Richard A Yetter, Committee Member
  • Adrianus C Van Duin, Committee Member
  • James Hansell Adair, Committee Member
Keywords:
  • Hypergolic propellant; Monomethylhydrazine; Tetramethylethylened
Abstract:
Current research is focused on the development of novel experimental techniques that can be used to obtain an understanding of the physical and chemical processes during the condensed-phase interaction of hypergolic pairs. A drop test setup, coupled with a high speed camera, was developed to conduct time-resolved studies on the pre-ignition, ignition and post-ignition events during the drop-on-pool impingement interactions of two hypergolic liquids. Thin-wire thermocouples were used to trace the temperatures of the liquid reactants as well as the gaseous products formed during the pre-ignition process which has a very short time scale. In addition, a confined interaction setup, coupled with rapid scan Fourier transform infrared (FTIR) spectroscopy, was developed to study the gaseous species evolved from the early reactions that occur upon the mixing of small quantity of liquid hypergols. One major objective of this research is to develop an understanding of the pre-ignition reactions between the oxidizer nitric acid (HNO3) and two target fuels: monomethylhydrazine (MMH), one of the most well-known hydrazine-based fuels, and N,N,N,’N’-tetramethylethylenediamine (TMEDA), which may be one of the most promising alternative fuels. This is also a part of an effort to provide experimental support for the MMH-RFNA and TMEDA-RFNA mechanisms that are being developed by the Army Research Laboratory (ARL). A three-stage hypergolic ignition process was revealed by both the temperature measurements in the drop tests and the pre-ignition products analysis in the confined interaction experiments. In the first stage, condensed-phase reactions take place between MMH (or TMEDA) and HNO3 upon their contact to form corresponding nitrate salts. The temperature at the interface between the two liquids increases rapidly to their boiling points due to the exothermic nitrate formation reactions. In the second stage, gas-phase reactions occur between the vapors of MMH (or TMEDA) and HNO3 to form a particulate aerosol which is mainly composed of nitrates products. In the third stage, secondary reactions are activated when the temperature of the gaseous and aerosol species increases to a critical point. Rapid heat release from the secondary reactions leads to an ignition in the gas phase. The early species (or pre-ignition products) formed in the three stages were analyzed by rapid scan FTIR spectroscopy and possible reaction pathways were proposed in this work. Two energetic nitrate compounds, MMH•2HNO3 and TMEDA•8HNO3, were synthesized from corresponding hypergolic pairs MMH/HNO3 and TMEDA/HNO3. Both of these two energetic nitrates have a stoichiometric F/O (fuel-to-oxidizer) ratio, thus can be treated as monopropellants. The combustion and thermal decomposition of these two compounds were studied in a strand burner and a confined rapid thermolysis (CRT)/FTIR setup, respectively. Combustion studies on these compounds provided first-hand burn-rate data for future use in premixed combustion modeling of the hypergolic pair MMH/HNO3 and TMEDA/HNO3. The decomposition reactions of these nitrates should also be considered as an important part in the MMH-RFNA and TMEDA-RFNA mechanisms.