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By means of photographic techniques, the size histories, ignition lags, and loci of ignition of small (100-300 microns diameter), single, freely falling fuel droplets suddenly exposed to a hot, oxidizing atmosphere in a furnace were determined as a function of initial droplet size, oxidizer temperature, fuel composition, and droplet spacing. The results show that ignition lag depends significantly on the temperature of the atmosphere, on the droplet-droplet spacing, and on the chemical nature of the fuel, but it appears to be only weakly affected by the oxygen concentration in the oxidizer. The ignition lag seems to be independent of the initial droplet size if the droplets are large enough to ignite at all. This characteristic insures that droplets with initial diameters smaller than a characteristic value will not ignite during their life-times. In spite of the complexity of the ignition process, the experimental results correlate satisfactorily with theoretical models that seem to represent a reasonable approximation to the physical situation of a spontaneously igniting fuel droplet.

Supersedes AD-295 494.

Supersedes AD-244 950.

Supersedes AD-259 548.

The kinetics of reaction between solid graphite and gaseous atomic hydrogen was studied in the temperature range 450-1200K. The products of reaction are molecular hydrogen and methane. The rate exhibits an activation energy of 5.55 kcal/mole and is a function of the concentration of both hydrogen atoms and hydrogen molecules. Near 800K the rate goes through a maximum value, probably because of the thermodynamic instability of methane. A mechanism for the reaction is proposed. (Author), Prepared in cooperation with Stanford Research Inst., Menlo Park, Calif.

The research reviewed in this report concerns the kinematics and kinetics of reacting gases of interest in advanced propulsion systems. The experimental measurements have included (1) the dynamics of interaction between atoms and solid surfaces, (2 0 the kinetics of gas-phase reactions involving atomic species (including chemionization), and (3) the transport parameters of high-temperature reacting gas mixtures containing atoms. New techniques have been developed to carry out the experimental measurements with chemical species of high reactivity and short lifetimes. The results have shown quantitatively the nonequilibrium behavior of exothermic gas-solid reactions, the role of energy transfer during homogeneous and heterogeneous collisions, and the magnitude of the interaction parameters applicable to high-temperature gas mixtures containing dissociated species. Some applications of these results to problems of propulsion and high-velocity flight are briefly explored in this report. These include (1) enhancement of specific impulse in hypersonic propulsion systems: (2) evaluation of the drag coefficient of a body in motion in rarefied atomic gases; (3) detection of atoms in high-velocity gas streams; and (4) analysis of boundary layers associated with chemical reaction., Prepared in cooperation with Stanford Research Inst., Menlo Park, Calif.