Initiation/ignition mechanisms

When pressure-decay rates less than critical are employed, the gas-phase combustion zone is removed from the propellant surface and extinguished, but not the ignition from within the condensed phase. Therefore, the temperature of the surface material will be above the autoignition temperature, and steady-state combustion will eventually be initiated. This mechanism is consistent with the observation that the luminosity of the combustion zone can vanish without combustion having been completely terminated. 

Fuze, Flare. A fuze, such as MT (mechanical time), to initiate ignition of the charge in a flare, which is a pyrotechnic item designed to produce a single source of intense light for purposes such as target and/or airfield illumination... 

Detonations can be initiated by ignition, mechanical impact, friction, or electromagnetic radiation, and physical confinement of the material is often but not always required. Thus, a sample of the potassium salt of 1-tetrazolylacetic acid placed on a surface at room temperature will explode if any part of the sample is heated to >200 °C (e.g. by a hot flint spark or a flame) [90]. If the conditions for detonation are met, the time between shock-initiation and detonation is about 1 ps only [91]. 

Johansson and co-workers (7, 8, 9) have shown that heat transfer from a compressed spherical bubble does not increase the temperature of its liquid surface sufficiently to account for the impact sensitivity of liquid explosives the high sensitivity of nitroglycerin is postulated as arising from the fact that small droplets are readily formed by the impact and ignited by the compressed air. Bolkhovitinov (1) postulated crystallization of the liquid under the impact pressure, with the phase transition causing the temperature increase which causes explosions. Bowden (3) favors the adiabatic compression of gas bubbles combined with the dispersion of the explosive into fine particles as the mechanism for initiation by mechanical impact. 

Note the similarity of this ignition mechanism with the one often used to initiate arc discharges by first establishing a contact between the two electrodes in order to heat them up. 

Pour or spoon the match heads, in a single pile, on the incendiary. Prepare the match heads for ignition with Fuse Cord 101) ox Improvised String Fuse (0102) in the normal manner. The fuse cord should terminate near the center of the match head pile. Concentrated Sulfuric Acid (0103) or a match flame can also be used as an initiator. Ignition takes place almost immedbtely on contact with the acid or the match ffame. Acid is recommended for use with specific delay mechanisms found in chapter 5. 

Thermal batteries are activated by applying an external signal to an initiation device that is incorporated in the battery. There are four generally used methods of activation electric signal to an electric igniter mechanical impulse to a percussion primer mechanical shock to an inertial activator and optical energy (laser) signal to a pyrotechnic material. 

Over the past 15 years, many studies have been conducted to determine the basic physical and chemical mechanisms of combustion and ignition. Although the studies have served to illustrate many of the overall characteristics of these processes, a quantitative characterization of ignition and of combustion has yet to be accomplished. The purpose of this article is to review the studies conducted to date, to indicate the significant accomplishments, and to show the areas which are not understood and therefore need further study. The discussion of ignition is presented first, since it is the initial stage of the combustion process. 

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