Flame Structure and Combustion Mode

On addition of AP particles to a double-base matrix, very fine luminous flamelet-sare formed from each AP particle at the burning surface, which diffuse into the dark zone of the base matrix. As the number of AP particles added to the base matrix is increased, the number of flamelets also increases and the dark zone is replaced with a luminous flame. 

When large spherical AP particles dg = 3 mm) are added, large flamelets are formed in the dark zone.Pl Close inspection of the AP particles at the burning surface reveals that a transparent bluish flame of low luminosity is formed above each AP particle. These are ammonia/perchloric acid flames, the products of which are oxidizer-rich, as are also observed for AP composite propellants at low pressures, as shown in Fig. 7.5. The bluish flame is generated a short distance from the AP particle and has a temperature of up to 1300 K. Surrounding the bluish flame, a yellowish luminous flame stream is formed. This yellowish flame is produced by in-terdiffusion of the gaseous decomposition products of the AP and the double-base matrix. Since the decomposition gas of the base matrix is fuel-rich and the temperature in the dark zone is about 1500 K, the interdiffusion of the products of the AP and the matrix shifts the relative amounts towards the stoichiometric ratio, resulting in increased reaction rate and flame temperature. The flame structure of an AP-CMDB propellant is illustrated in Fig. 8.1. 

When the mass fraction of AP is increased, the dark zone of the base matrix is eliminated almost completely and the luminous flame approaches the burning surface as shown in Fig. 8.2(a). For reference, the flame structure of an RDX-CMDB propellant is also shown in Fig. 8.2(b). Since RDX is a stoichiometrically balanced 

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Inherently flame and heat resistant fibers are either all-aromatic polymeric structures or inorganic and mineral based. The aromatic fibers are mostly used for apparel applications as protective clothing. Some commonly used fiber types are given in Table 24.1 and discussed subsequently. These are nonthermoplastic, combustion-resistant with decomposition temperatures above 375°C3 and with LOI values 30 vol % or more. Moreover, they have char-forming tendency. For detailed information about their chemical structures and mode of decomposition, the reader is referred to a review by Bourbigot et al.91... 

This implies that the spray tends to approach a saturation state unless additional heat and oxygen are supplied from the outside of the spray stream. It also implies that the behavior of the outer diffusion flame dominates the subsequent evolution of spray combustion from the spray boundary side. In real spray combustion, this boundary-layer type of change occurs dynamically because the boundary of the spray stream is located in the coherent vertical structure of the shear layer. In addition, turbulent effects are inevitable. However, such fluid dynamic effects have not yet been well characterized. Therefore, we focus on the behavior of the outer diffusion flame based on a quasi-steady continuum spray model. Chiu s theory is developed on this basis to classify the combustion modes excited by the penetration of the outer diffusion flame into the spray region. 

Since each element of a real spray changes its state with time or along its path line, the possible mode of flame penetration into the spray element changes depending on when a part of the spray element boundary is ignited. Combining the temporal change of the spray element state and the possible flame penetration mode, we can determine the structure of the spray combustion. In this section, we consider the temporal evolution of the spray element. 

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