Ignition phase

After the ignition phase, water is fed to the reactor and the 02 CH4 and H20 CH4 ratios are varied until the desired operating conditions are reached. It must be noted that after the ignition phase, due to the lower values of the 02 CH4 ratio, the homogeneous combustion of methane is inhibited and consequently POX, SR and WGS reactions occur simultaneously in the catalytic bed, while the temperature on the SiC foam decreases to values lower than 400 °C. 

During the ignition phase, as the pressure increases, the propellant is loaded by hydrostatic pressure imposed on a biaxial tensile stress field. Because the propellant is incompressible in the ignition condition, the pressure is transmitted entirely to the case, which, being thin because of the weight requirement, presents significant hoop deformations. Therefore, a tensile strain... 

Figure 3. Schematic representation of pressurization during the ignition phase.

Equation (2.10), together with the partial equilibrium relationships, determines a fully ignited composition which approximately describes the junction between the ignition phase of the reaction and the purely decelerating association phase which follows it. The sizable concentrations of the intermediates OH, H and O in this composition account for the magnitudes of the essential overshoots of these species which arise early in the main reaction simply because N must decrease in order for the reaction to be completed. To be sure, individual excursions of the concentrations of these intermediates above these fully ignited partial equilibrium values are possible before the individual bimolecular equilibria are approached, but such excursions are short-lived in comparison to the overshoots that depend upon association for their removal. Under many drciunstances, particularly in near-stoichiometric mixtures, no such excursions occur and the fully ignited composition represents upper bounds to the observed concentrations of the intermediates. 

The octane number is a measure of a fuel s ability to resist auto-ignition during the compression phase prior to ignition. 

Lead Azide. The azides belong to a class of very few useflil explosive compounds that do not contain oxygen. Lead azide is the primary explosive used in military detonators in the United States, and has been intensively studied (see also Lead compounds). However, lead azide is being phased out as an ignition compound in commercial detonators by substances such as diazodinitrophenol (DDNP) or PETN-based mixtures because of health concerns over the lead content in the fumes and the explosion risks and environmental impact of the manufacturing process. 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

Many of the procedures used for technical analysis of aluminum hydroxides are readily available from the major producers of aluminum hydroxides. Phase Composition. Weight loss on ignition (110°—1200°C) can differentiate between pure (34.5% Al(OH)2) ttihydroxides and oxide—hydroxides (15% Al(OH)2). However, distinction between individual ttihydroxides and oxide —hydroxides is not possible and the method is not useful when several phases are present together. X-ray powder diffraction is the most useful method for identifying and roughly quantifying the phase composition of hydroxide products. 

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

Addition of 15% gasoline to methanol to produce M85 fuel is an alternative. At temperatures above —6.7° C, reHable ignition of M85 fuel occurs because the gasoline provides the vapor phase necessary for ignition under choked condition. 

Reaction/Ignition or thermal decomposition due to high temperature at unwetted internal heating element surface. Possibility of runaway reaction, vapor phase deflagration or thermal decomposition. 

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