Combustion and extinction in the stagnation-point boundary layer of a condensed fuel

The combustion of solid fuels has been studied by using a solid fuel ramjet combustion chamber equipped with a vitiated air heater. The fuels were polyethylene (PE) and hydroxyl-terminated poly butadiene (HTPB), with PE being the prevailing fuel. The air was heated by combustion of hydrogen and oxygen. In order to get a better understanding of the combustion process, a thermocouple and a gas-chromatogr aphic technique were used to obtain temperature and species concentration profiles throughout the combustion chamber. The measurements were taken at several axial and radial positions of the combustion chamber, including measurements in the recirculation zone of the flameholder and in the afterburner chamber. The influence of different test conditions, like mixture ratio, inlet temperature, and mass flux, was also investigated. The results are discussed with regard to flame position, turbulent mixing, and combustion efficiency.

Temperature and Concentration Measurements in a Solid Fuel Ramjet Combustion Chamber

The regression rate of a fuel for hybrid propulsion applications results from the coupling between the heat flux density issuing from the reacting cross {Jow and the energy required by the condensed phase process. Three fuels are considered polyethylene, a reference material for laboratory scale investigation, hydroxyl terminated polybutadiene, a candidate material for booster applications, and glycidyl azide polymer. which although being a fuel has an autonomous burning rate. The condensed phase process is shown to be an irreversible thennal pyrolysis not directly affecred by pressure. The characteristics of this process are presented for the three fuels. The ablation process, measured here or in the literature on laboratory devices or small motors, can be described quite accurately by the diffusion flame approach for the pure fuels. The ablation of GAP is dominated by its self burning with probably some added effect of the cross flow difTusion flame, with, as a consequence, high regression rates.

Condensed-phase behavior and ablation rate of fuels for hybrid propulsion

Nutation dampers vs precession dampers for asymmetric spinning spacecraft.

Numerical analysis of combustion characteristics of hybrid rocket motor with multi-section swirl injection

To characterize the kinetics of the linear pyrolysis of polymers under combustion conditions,impinging-jet diffusion-flame experiments were conducted on seven different polymers (linear and crosslinked polymethylmethacrylate, polyethylene, polypropylene, Delrin, Nylon 6-6, polyurethane). Surface brightness temperatures typically of 500° to 600°C, were determined by infrared spectraradiometry, and were correlated with linear-pyrolysis rates, typically 0.08 to 0.4 mm/sec, using Arrhenius expressions. The observed apparent activation energies for linear pyrolysis could, in some cases (polypropylene, Delrin, Nylon 6-6, polyurethane) be correlated with bulk-pyrolysis data from the same polymers. In other cases (linear and crosslinked polymethylmethacrylate, polyethylene), further experimental testing and analytic modeling appear necessary before rational correlations can be made.

Linear pyrolysis of various polymers under combustion conditions

: A means for producing combustion of polymers under well-controlled conditions has been employed for study of their fundamental combustion characteristics. In the subject work, a planar diffusion flame is established between an axi-symmetric, 'stagnation-point' flow of gaseous oxidant and the pyrolysis product vapors emerging from the polymer surface lying below. Surface regression rate, surface temperature, and oxidant mass flow rate (the principal control variable) were determined. Plexiglas, Plexiglas-55, polyethylene, polypropylene, Delrin, nylon 6-6, ICRPG polyurethane binder, and polystyrene were tested. Surface regression rate and surface temperature were correlated by means of an Arrhenius function, and these results are utilized to examine previously proposed models of the surface pyrolysis process. The surface regression rate and oxidant mass flow rate were used with a fluid-dynamic analysis of the combustion region to predict the effective heat of gasification for each of the above mentioned polymers. Applications and implications of the above findings are discussed. (Author)

An Investigation of the Combustion Characteristics of Some Polymers Using the Diffusion-Flame Technique.

Effective heats of gasification of polymers under combustion conditions

: Air-breathing reciprocating engines and gas turbines fueled with hydrogen are treated with special concern for the problems each might encounter if used on a large scale. The potential improvements in performance of each power plant when operated with hydrogen are determined using prior analytical and experimental data and/or new estimates. Particular attention is given to factors which might improve conversion efficiency and discount, at least partially, the relatively high cost of hydrogen energy. Previous operating experience and analysis of gas-turbine operation on hydrogen are considered. Hydrogen-fueled gas turbines are found, unlike reciprocating engines, to offer relatively modest thermodynamic performance gain compared with hydrocarbon fueling, though LH2 fueling has substantial potential (undemonstrated) for power-plant efficiency or reliability improvement through hot-section cooling and/or heat regeneration. LH2 fuel-system problems with transient response as well as inavailability of suitable hardware are most evident, though probably resolvable by substantial state-of-the-art development.

Hydrogen Energy Conversion

: Two efforts are reported as a continuation and termination of previous work: (1) modelling of the deflagration of ammonium-perchlorate(AP)-oxidized composite solid propellants, (2) measurements of linear-pyrolysis rates of pure and catalyzed AP. Modeling efforts led to development of a new comprehensive model of AP composite propellant burning. The model is termed the 'modified granular-diffusion-flame model'. Linear pyrolysis experiments corroborated earlier data by another experimenter. New pyrolysis-rate measurements were made with catalyzed AP and with different radiometric wavelengths for surface-temperature measurement. Interpretation of these results was cut short by program termination. (Author)

Richard B. Cole

Papers

Linear pyrolysis of various polymers under combustion conditions

An Investigation of the Combustion Characteristics of Some Polymers Using the Diffusion-Flame Technique.

Effective heats of gasification of polymers under combustion conditions

Hydrogen Energy Conversion

Experimental Study of the Composite Solid Propellant Deflagration Process on a Fundamental Level.