| Combustion is a main path for energy utilization. Nowadays, along with the boom of economy, the demands for energy is becoming increasingly intensifying, which lead to the requirements for the specific characteristics of different fuels, including the combustion stability, insensitivity, mechanical property, energy density, burning rate, characteristic signals, exhaust pollutions etc., aiming at adapting various applications. Propellant is a kind of fuels composed of energetic materials, and applies to provide the aerospace crafts with propulsion energy. The previous researches were once used to focusing on making propellants exhibit high-energy performances, and there is a great deal of relevant references. Whereas, together with the rapid development of aerospace technology, some new needs has arisen besides the demands for high specific impulse, for example, the increasingly developed micro-propulsion systems that are used to fulfill the requirements of maintaining the formate and tracking for spacecrafts, the abutting joint between space shuttle and space station, the orbit transfer of satellites, and so forth. These demands ask for the development of propellants with high combustion stability, outstanding controllability and low burning rate, as well as low sensitivity and less pollution. Motivated by these issues, I have chosen two new type fuel systems, and studied their thermal decomposition and combustion mechanisms in this dissertation.The dissertation can be logically divided into two parts. Part I focuses on the experimental and theoretical studies of thermal decomposition and combustion of high-energy solid GAP/B based propellant. Both the advantages and disadvantages of B used as a propellant component are discussed, and some coating processing methods are proposed for improving ignition and combustion performances of B. Thermal decomposition investigation of GAP was carried out in detail. The nitrogen elimination reaction has been attracting great research interests due to its high energy release in short time. Thus, the nitrogen elimination for one monomer have been explored with B3LYP/6-31G(d)//G2 method, and the reaction channels were identified, and the relative energies of reactant, product and intermediates were presented simultaneously. As to the combustion study of GAP, the free-energy minimization method was introduced to calculate the combustion temperature and mole fractions of final products under normal pressure adiabatic condition. Several exploratory boron-contained propellants were prepared, and some important parameters were tested and analyzed. PartⅡpays much attention to experimental investigations of Al/H2O based fuel. Al powders with three particle sizes were put to use in ignition tests under different pressures to determine the suitable fuel component Al. The flash pyrolysis of the key addition agent polyacrylamide in argon were carried out at 300℃, 450℃, 600℃, respectively, and the formation mechanism for liquid and gas products, as well as the effects on improving the characteristics of Al/H2O propellant were discussed. Moreover, the influences of some other addition agents, including amorphous state nano-B/Co alloy, HMX, RDX, AP, CL-20, etc., were studied, and some basic parameters were preliminarily obtained. Otherwise, the new concept of micro-propulsion system was described in some extent, and a kind of ideal fuel material, Methylmethacrylate (MMA), for this application was presented. Also, it was supposed to work as the combustion stabilizer and improver for Al/H2O based propellant. Then, the laminar premixed lean combustion of MMA was carried out by tunable synchrotron radiation VUV photoionization molecular beam mass spectrometry. The species in the flame were identified by their PIE spectra, and displayed the relevant mole fraction profiles together. What is noteworthy is that the more vivid understanding of thermal decomposition of GAP was newly formed, and the combustion mechanism of MMA was comprehensively studied for the first time, which would definitely provide some valuable information for mathematical and physical modeling. The optimal composition of Al/H2O propellant in Ar environment was proposed. This demonstrates that the dissertation has certain originalities.The findings obtained from the above researches are summarized as following.(I) Recent research progresses on GAP/B and Al/H2O based fuels, including some basic properties, the combustion behaviors, the improvement methods for fuels' characteristics, and so forth, were reviewed.(Ⅱ) An analytical method was employed to accurately measure the B wt% and B2O3 wt%, and other impurities were quantitatively measured by AAS and ICP. Two chemical coating methods, i.e., recrystallization and neutralization deposit, were proposed to treat B powders, aiming at improving its ignition and combustion characteristics. AP and LiF were used as the coating materials. The coating effects were analyzed by DSC and ignition testing, and more comparisons about the practicability underwent when coated B acted as the propellant component. The results showed that the double-layer coating methods exhibited the outstanding ignition and combustion performances. (Ⅲ) Laser light scattering method was introduced to proceed the in-situ characterization of the polymer properties of GAP. The results show the number average molecular weight and the mass average molecular weight are 3981 and 5497, respectively, thus the diversity is 1.38.(Ⅳ) Thermal decomposition of uncured GAP and GAP coated Boron (BGAP) under normal pressure in air or N2 was investigated by TG/DTG and in-situ FTIR combined with pyrolyzer, and some kinetic parameters for the first weight loss process were calculated by Kissinger method. The results showed that BGAP exhibited different decomposition behaviors from pure GAP, including much lower initial temperature and different reaction pathways demonstrated by the formation of some special groups. The activation energies for the first decomposition step of both pure GAP and BGAP in air were respectively smaller than that in N2. Moreover, the activation energy of BGAPwas smaller than that of pure GAP. These indicated that the existence of Boron did induce the reaction mechanism variate to some easy-proceeding path. The reaction pathway for the nitrogen elimination step was studied by the Gaussian 03 method, B3LYP/6-31G(d)//G2; the structures and the energies of reactants, transition state, intermediates and products were calculated. Thermal decomposition of GAP under low pressure in Ar was studied by tunable synchrotron radiation VUV photoionization reflectron time-of-flight mass spectrometry combined with molecular beam sampling technology. The thermal decomposition of GAP was found to begin at about 70℃,and the products are basically with low molecular weight. The production amount of ammonia is small at low temperature thermal decomposition stage, but increases a lot at the high temperature. Many intermediates and free radicals have been identified with the measurements of photoionization mass spectrum and the PIE spectra by scanning photon energies. Azide radical has been detected. The possible ionization energies of some thermal decomposition species, such as vinyloxy radical, acetyl cyanide, 3-azide propylene et al., were given.(V) Combustion of GAP under normal pressure adiabatic condition was theoretically investigated by free-energy minimization method, and the combustion temperature was calculated to be 1475 K, and the mole fractions of the products are: 0.2238 N2+ 0.2842 C + 0.1402 CO + 0.1200 CO2 + 0.0219 CH4 + 0.3220 H2+ 0.0067 H2O.(Ⅵ) A series of high Boron content propellants contained various Boron powders (coated & uncoated) and binders (GAP & HTPB) were prepared, and the basic characteristics were measured in a laboratory-scale combustion chamber installation with two parallel glass windows by several experimental approaches. The results show that BGAP (1:0.3) has the obvious advantages for being used as the incendiary agent of propellants.(Ⅶ) A variety of experimental methods were employed to detailed study Al/H2O based fuels. Firstly, the average particle size of Al powders used was confirmed to within nanometer scale, which would be ignited under relative temperate conditions. Then, flash pyrolysis investigation of polyacrylamide (PAM) solution was carried out in an off-line furnace-type pyrolyzer at 300℃, 450℃and 600℃with Ar as the carrier gas, and many flammable compounds were identified by GC/MS in liquid products, especially some cyclic nitrogenous substances, i.e., 1,2,4-Triazine-3,5(2H,4H)-dione, 5-Nitro furfural semicarbazone, Hexadecanamide etc., were considered to release much energy under combustion condition. There were just a few gas products formed at 600℃, which were all flammable small molecules and believed to favor the combustion of the propellants. The FTIR results showed that the contents of tar and char compounds in residues increase as the temperature increasing. The addition of PAM evidently improved the burning rate and energy release of propellants, as well as decreased the pressure exponent -60%.(Ⅷ) Amorphous state nano-B/Co alloy was prepared. Both XRD and SEM tests were carried out to determine the average particle size to be -21 nm. It was then used as an addition agent for basic Al/H2O based propellant, and some regular parameters were measured. The results showed it had an obvious promotion effects compared to the blank recipe, for example, the burning rate and the detonation heat in 1 MPa Ar were increased by 4.52 mm·s-1 and 718.53 J·g-1, respectively. However, adding the oxidizers widely used in solid propellants, such as AP, HMX, RDX, CL-20 etc., into Al/H2O propellants increased the ignition threshold, and unexpectedly leaded to the degradation of combustion performances. A competition reaction mechanism was preliminarily proposed to explain the phenomena. It could be conjectured that under-water propulsion engine should be equipped an additional oxygen-containing accessory in order to make the most of the advantages of these oxidizers.(Ⅸ) A fuel-lean laminar premixed methylmethacrylate/oxygen/argon flame at 2.67 kPa with an equivalence ratio ((?)) of 0.75 has been investigated with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular beam sampling mass spectrometry techniques. Isomers of most observed species in the flame have been identified by measurements of photoionization mass spectra and the near-threshold photoionization efficiency spectra. Mole fraction profiles for about 42 flame species are displayed. Combined with the mole fraction profiles, the formation mechanisms of the free radicals, oxygenated compounds and other molecular intermediates are proposed. C3H2O was found to be the key radical in the whole combustion process for the first time.(Ⅹ) Finally, based on the variety of experimental results, the optimal recipes of Al/H2O based propellants under Ar were proposed for adaptting to different demands, which were (a) nano-Al+1 wt% PAM solution+5 wt% B/Co+ MMA (<5 wt%); (b) nano-Al+3 wt% PAM solution+5 wt% B/Co+ MMA (>5 wt%), and mAl:mH2O=1:1. (a) would be with high energy release, low pressure exponent, relative high burning rate, outstanding combustion stability and excellent combustion efficiency for Al. (b) would possess the characteristics of high energy release, high pressure exponent, more higher burning rate, and good combustion efficiency for Al.
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