Central ignition

S has been approximated for flames stabili2ed by a steady uniform flow of unbumed gas from porous metal diaphragms or other flow straighteners. However, in practice, S is usually determined less directly from the speed and area of transient flames in tubes, closed vessels, soap bubbles blown with the mixture, and, most commonly, from the shape of steady Bunsen burner flames. The observed speed of a transient flame usually differs markedly from S. For example, it can be calculated that a flame spreads from a central ignition point in an unconfined explosive mixture such as a soap bubble at a speed of (p /in which the density ratio across the flame is typically 5—10. Usually, the expansion of the burning gas imparts a considerable velocity to the unbumed mixture, and the observed speed will be the sum of this velocity and S. ... 

Strehlow (1981) elaborated these recommendations for a number of cases including a centrally ignited cylinder slice. This resulted in a remarkable result ... 

Figure 2. The Radiant Panel Test was designed to measure both critical ignition energy and rate of heat release. A sample is mounted facing a controlled heat flux but at a 3CP angle to it such that the upper part of the specimen is more severely exposed. Since irradiance decreases down the specimen, the time progress of ignition down the specimen serves to measure central ignition energy. Thermocouples in the stack above the specimen serve as a measure of heat release rate.

Our conception ascribes an essential role to braking of the gas by the tube walls. Experiment shows that as the tube diameter increases the distance at which detonation arises also increases. In spherical bombs with central ignition occurrence of detonation has never yet been observed. 

Several methods of attacking the problem were devised, namely, central ignition m a large glass globe by means of an electric spark ... 

Parker,8 using a glass globe with central ignition similar to that figured on p. 92, determined the lower limits of inflammation of... 

Effect of vessel shape and increased initial pressure. The maximum explosion pressure in confined vessels is not significantly affected by the volume or shape of the vessel in confined explosions for vessels that approximate the cubic shape, that is, with a ratio of diameter to length (or vice versa) of about 1 1 to 1 1.5. In closed elongated vessels with central ignition, spherical ignition of the flame front will cause the flame to proceed swiftly in an axial direction. In the process, it compresses... 

The relevant flammability data is obtained in a specially designed 20 litre sphere. The main features of this explosion vessel include Hastelloy C 276 walls, central ignition with spark, hot wire or pyrotechnic ignition source, 200 bar pressure resistance, ambient to 300°C initial temperature, easily opened for frequent cleaning. This apparatus allows precise determination of the flammability limits, autoignition temperature, explosion overpressure, rate of pressure rise and flame speed. A review of flammability data in chlorine is given. 

The approximate pressure rise AP at any instant t after the central ignition of a flammable mixture at temperature Ti in a spherical enclosure that does not fail is... 

The thermite charge is centrally Ignited, as shown in Fig. 1. Reaction of the thermite is accelerated by fracturing of the billet due to internal stresses set up by rapid heating of gases trapped In the internal pores and possibly by vaporization of thermite components and... 

External events are accident initiators that do not fit well into the central PSA structure used for "internal events." Some "external events" such as fire due to ignition of electrical wires, or flood from a ruptured service water pipe occur inside the plant. Others, such as earthquakes and tornados, occur outside of the plant. Either may cause failures in a plant like internal events. External initiators may cause multiple failures of independent equipment thereby preventing action of presumably redundant protection systems. For example, severe offsite flooding may fli 1 the pump room and disable cooling systems. An earthquake may impede evacuation of the nearby populace. These multiple effects must be considered in the analysis of the effects of external events. 

FIGURE 6.12 A bomb calorimeter is used to measure heat transfers at constant volume. The sample in the central rigid container called the bomb is ignited electrically with a fuse wire. Once combustion has begun, energy released as heat spreads through the walls of the bomb into the water. The heat released is proportional to the temperature change of the entire assembly. 

The larger rifles such as the familiar military rifle use cartridges of the type shown in Fig. 19.3. The relatively heavy base contains centrally a pyrotechnic percussion igniter (cap) and also a rim on which the ejector mechanism operates. Bullets can be made of various materials, but the detailed construction depends on whether they are to be used for armour piercing, anti-personnel, incendiary or tracer purposes. In operation, the primer is fired by the striking pin of the rifle, the propellant ignites and the... 

Premature ignition can be reduced or eliminated by redesigning the fuel delivery system, which can be categorized into three types central-, port-, and direct injection. Central and port fuel injections form the fuel-air mixture during the intake stroke. In the case of central injection (or a carburetor), the injection is at the inlet of the air intake manifold. In the case of port injection, fuel is injected at the inlet port. Direct injection is technologically sophisticated and involves forming the fuel-air mixture inside the combustion cylinder after the air intake valve has closed [27-36]. 

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