Detonation quenching

An equality may be used in equation (30) to define approximately a general condition for detonation quenching. If for order-of-magnitude purposes, dT /dx is approximated as T /l, then this equality becomes dA/dx A/(21X in which / may be estimated from experimental results (for example, [123] [125]). 

Therefore, it is possible to observe the spatial orientation and displacement of the heat release fronts (combustion, deflagration, detonation) and their reciprocal transformation (deflagration/detonation transition, detonation quenching). It is important to find an answer to the question what optical recording systems and in what combination with the known ways of measurements are applicable for solving the assigned problems ... 

Dry type deflagration and detonation flame arresters have an internal arrester element (sometimes called a matrix) that quenches the flame and cools the products of combustion. A great number of arrester elements have been developed and used. The most common types currently available are as follows ... 

Snccessful full-scale tests on quenching of deflagrations and detonations using expanded metal cartridge flame arresters were performed to USCG standards on Group C and D gases by Westech Industrial Ltd. (Lapp 1992, Lapp and Vickers 1992). 

The apertures in sintered metal elements can be made so small that this arrester is able to quench detonations provided that it has sufficient mechanical strength. Particular care is required to ensure a secure anchorage of the sintered element to prevent leakage around the element caused by the impact of the shockwave (HSE 1980). 

The preceding section described the state of transition expected in a deflagration process when the mixture in front of the flame is sufficiently preconditioned by a combination of compression effects and local quenching by turbulent mixing. However, additional factors determine whether the onset of detonation can actually occur and whether the onset of detonation will be followed by a self-sustaining detonation wave. 

Superfine PETN for use in EBW detonators and MDF is produced by quenching a hot ace tone soln in cold water. The resulting particle size distribution averages 10 microns, and irregular crystals are produced which are easier to initiate (Ref 80a)... 

Transition to detonation caused by instabilities near the flame front, the flame interactions with a shock wave, another flame or a wall, or the explosion of a previously quenched pocket of combustible gas... 

As in consideration of deflagration phenomena, other parameters are of import in detonation research. These parameters—detonation limits, initiation energy, critical tube diameter, quenching diameter, and thickness of the supporting reaction zone—require a knowledge of the wave structure and hence of chemical reaction rates. Lee [6] refers to these parameters as dynamic to distinguish them from the equilibrium static detonation states, which permit the calculation of the detonation velocity by C-J theory. 

Rarefaction waves are generated circumferentially at the tube as the detonation leaves then they propagate toward the tube axis, cool the shock-heated gases, and, consequently, increase the reaction induction time. This induced delay decouples the reaction zone from the shock and a deflagration persists. The tube diameter must be large enough so that a core near the tube axis is not quenched and this core can support the development of a spherical detonation wave. 

As in the case of deflagrations, a quenching distance exists for detonations that is, a detonation will not propagate in a tube whose diameter is below a... 

The deficiency can be made up, if no energy is added from the outside, only from the detonation products, with a resulting drop in their temperature from the isochoric adiabatic flame temperature. This may quench the chemical reaction. The deficiency diminishes with decrease of wave-front curvature. For point initiation , enough energy must be added from the outside to make up for the total deficit which accumulates during the time the wave is reaching a diameter at which the curvature drops below a critical value... 

In other words, all expls detonated from a point will quench unless the booster develops a deton front having a radius of curvature greater than the min for the expl being boostered. The thickness of the deton front is taken as that of a typical shock front, ca IO-5 cm... 

Thus, as noted in Ref 12a, p 4, the chemical reaction in normal detonation includes a fast first stage and a slow second stage. The low-order detonation is supported by only the first the second is too slow for completion in the available time or is quenched as a result of lateral expansion or other loss mechanism... 

C(v,P). It is seen that the temp of the spike N is somewhat lower than half of the C-J temp. Since the temp is low, it is not expected that the chem reactions could occur to any appreciable extent in the short time required for the gas to pass thru the initial shock. Actually the temp at Njis so low that in many practical cases one would expect a time lag or a quenching zone before the reaction sets in. Hirschfelder inferred that accdg to NDZ theory some chem reaction can take place within the detonation front (in cases of unusually high reaction rates), and blunt the von Neumann spike, as can be seen in Fig 4 (Ref 7, pp 172-74)... 

Cook (Ref 2) reported that an inert additive, such as fine NaCl, in amts up to 10% with RDX,vaporizes in the detonation wave and does not affect its rate, but if used in higher proportion the deton can be quenched. On the other hand, coarse NaCl (-10+30 mesh) can be added in amts up to 90-95% to fine grained RDX without quenching detonation. Coarse granules of salt allow the deton to propagate between the grains at or near the rate of the pure expl... 

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