Combustion of Liquid Explosives

Combustion reaction of explosives is deflagration, which is another classic form. Deflagration is different from general combustion. Explosives have oxidants and combustible materials. Combustion of explosives does not need the oxygen in air, and it spreads smoothly. For propellants and pyrotechnics, combustion is the basic form of explosion. Some primary explosives work through combustion or combustion-detonation. Here in all, study of the general rules of liquid explosives and the basic conditions of combustion-to-detonation are of great importance for the safety productions and applications of liquid explosives. 

Combustion is very common, e.g., combustion of wood, coal, etc. The chemical reactions with light and heat released are combustion. The space with light and high temperature of chemical reaction is named as flame. The geometric surface of separating burning layer from nonreaction zone is the flame front. 

The combustion of liquid explosives leads to violent chemical reactions, which spread themselves. It is different from the combustion of general fuels. The combustion of liquid explosives can be isolated from air, and the oxidations depend on the oxygen of the explosive. This combustion is also deflagration. The processes of explosive combustion are the processes in which flame fronts spread themselves [1]. Spreading of flames is determined mainly by conduction of heat and diffusion of combustion productions [2]. 

Burning speed is an important parameter of combustion. There are two ways to show the burning speed linear speed of flame front spreading and mass speed of combusted liquids. The linear speed (w) of flame front spreading along the liquid 

V represents the bumed/combusted volume within unit time S represents the total surface area of flame fronts. 

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Meanwhile, in 1938 at the AS USSR Institute of Chemical Physics A. F. Belyaev showed that the combustion of liquid explosives occurs in the gas phase after their evaporation. In analogy with this, Ya.B. proposed a theory of combustion of a solid powder (24) according to which the powder is heated in the solid phase and then decomposes, transforming into a gas it is only in the gas phase, at some distance from the surface, that the bulk of the chemical energy is released. Ya.B. also pointed out the peculiar effects of... 

To simplify the flame propagation, the assumption is based on flame propagation with a fixed speed toward the liquid in only one dimension. Butyl nitrate is filled in a pipe. The ignition device is used to induce the combustion of liquid explosives from one end. At first, only the explosive (which is very close to the ignition device) starts burning. The propagation of flames is shown in Fig. 2.1. 

Fig. 2.2 Schematics of evaporation-combustion of liquid explosives A condensed phase B production of combustion Tq, T, Ti-temperature distribution curve...

Sensitivity and Hazards ofLP. Some mono-proplnts and some well-mixed biproplnts exhibit detonation characteristics typical of Liquid Explosives (See Sects 4 5 of article on Liquid Explosives in this Vol). However, biproplnts usually do not sustain complete detonation, ie, a rather small portion of the biproplnt undergoes something akin to detonation and the remainder deflagrates (Ref 26). Of course even this partial detonation can be very dangerous and destructive. LP are also subject to another phenomenon which is potentially destructive (at least to the rocket), namely combustion instability (Refs 16 22)... 

To simplify the studies on the composition and detonation properties of liquid explosives, their components will be divided into elements, oxidizers, combustible agents, and additives for composition description in this book. However, when detonation properties are discussed, the classification method will be based on their characteristics. 

The combustible agents of liquid explosive mixture include hydrocarbons, nitro compounds, hydrazine, and aluminum. The combustible agents used in condensed composite explosives can be used as combustible agents of liquid explosives. 

Raw Materials and Formulation of Liquid Explosives Table 1.2 Properties of common combustible agents [1]... 

Liquid explosives are noncompressible, and are different from condensed explosives. In the explosion, liquid explosives should be gasified first, later ignited. Once this abnormal combustion reaction becomes normal one, self-sustaining spread detonation follows. The explosion changes of liquid explosives have two classic forms combustion and detonation. 

Combustion process has stable and unsteady combustions. The stable combustion of explosives presents that single component explosive has a constant burning/ combustion speed under certain conditions (e.g., fixed pressure, temperature, packed density, etc.). Most of liquid explosives can reach stable combustion. The combustion of explosive is not always stable. For mixed liquid explosives, the combustion speed may accelerate or slow down, sometimes accelerate or slow down suddenly. The main reason is the nonuniformity of mixtures. 

In the deduction of the explosive combustion, study of liquid and solid explosives separately is not a must. When heat is transferred to the solids, they start to liquefy. And the liquids follow the above combustion rules. Figure 2.2 indicates that the combustion of condensed explosives is similar to that of flammable gases under steady condition. The only difference is that for gas combustion aU mixtures are gases while the gases are obtained by evaporation of liquids. 

In stable/steady combustion, the combustion speed of liquid explosives has a relationship of Eq. 2.18 with pressure. 

It is believed that after the stable combustion is broken, the explosion rates of explosives straighten up until stable detonation occurs. But the writer does not agree with it. In the writer s opinion, there is a deflagration stage between unsteady burning and normal detonation. It is also the new discovery from the explosion characters/features of liquid explosives. 

These two forms of explosion of liquid explosives can interchange with each other. In certain case, combustion may transform into unstable detonation and further evolute into stable detonation. 

To study the detonation of liquid explosives and its spreading/transportation, nitromethane, nitroglycerine, diethyleneglycol dinitrate, and methyl nitrite are designed as the objectives of liquid explosives to study the chemical dynamics and the complex unsteady process of shock waves combustion. These phenomena determine the structure of detonation wave fronts and spreading limit of detonation waves. They help to clear the flow dynamics of wave fronts, and refer suggestions for the formula of liquid explosives, study and application of equipment features. They help to improve and perfect the detonation theory. 

This equation is good to calculate, relatively accurately, the combustion heat of liquid explosives. While, in the calculation of combustion heat of solid explosives, the right part of equation must be deducted off its fusion heat. If the substance is gas, the vaporization heat should be added. In this method, the standard temperature used is Tb = 298.15 K. 

In order to further show the formation heat of liquid explosives, combustion heat and formation heat of nitroglycerine will be calculated in detail as an example. 

The theory explains why a succession of shocks may occur in BLEVEs. A first shock is produced by the escape of vapor, a second by evaporating liquid, a third by the second shock of the oscillating fluid bubble, and possible additional shocks produced by combustion of released fluid. It is also possible for these shocks to overlap each other, especially at greater distances from the explosion. 

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