Igniter reaction

C. Campbell, Pre-Ignition and Ignition Reactions of the Pyrotechnic System Zn-C6Clfi- KC104 in 5th Symp Combstn (1955) 227... 

In the search for a better approach, investigators realized that the ignition of a combustible material requires the initiation of exothermic chemical reactions such that the rate of heat generation exceeds the rate of energy loss from the ignition reaction zone. Once this condition is achieved, the reaction rates will continue to accelerate because of the exponential dependence of reaction rate on temperature. The basic problem is then one of critical reaction rates which are determined by local reactant concentrations and local temperatures. This approach is essentially an outgrowth of the bulk thermal-explosion theory reported by Fra nk-Kamenetskii (F2). 

Sodium hydride ignites in oxygen at 230°C, and finely divided uranium hydride ignites on contact. Lithium hydride, sodium hydride and potassium hydride react slowly in dry air, while rubidium and caesium hydrides ignite. Reaction is accelerated in moist air, and even finely divided lithium hydride ignites then [1], Finely divided magnesium hydride, prepared by pyrolysis, ignites immediately in air [2], See also COMPLEX HYDRIDES... 

Ignition Reaction occurring when a combustible material such as an explosive is heated to or above its ignition temperature. 

Mixtures of natural gas and air are similarly unpredictable, being quite stable and unreactive until a spark or a hot surface ignites reaction, and then thermal and chain branching autocatalysis takes off and so does the building. 

Recently, a set of correlations including the effect of channel shape has been proposed by Ramanathan et al. (2003) on the basis of solution of the Navier-Stokes equations in the channel, with different solutions derived for ignited-reaction and extinct-reaction regimes. The comparison of various empirical and theoretical correlations with experimentally evaluated mass transfer coefficients is given by West et al. (2003). The correlations by Ramanathan et al. (2003) or Tronconi and Forzatti (1992) have been used in most simulations presented in this chapter. 

Japan 1967, 28(2), 154—58(Japan) From CZ 1968(42), Abstr No 2922 CA 70, 49151j (1969) (Explodability of AN-metal powd systems was investigated by means of shock-sensitivity tests and the Knipp Ignition Test. The results were dependent on the type of metal. The ignition point decreased in the order of metals Znactivation energy of the ignition reaction was ealed from die ignition-delay-time at different temps)... 

Levedahl (106) noted that aliphatics from acetylene to octane all gave hot flames at 600° C. He suggested that some reaction, such as thermal decomposition, which was common to all aliphatics, became important. Benzene showed a very high, inconsistent hot flame limit, while cyclohexane was low and variable. Levedahl believed the cool flame and subsequent reaction, along with compression, served to raise the mixture temperature to the critical value. Acetylene was believed to play a major role in the ignition reaction. 

Fig 4 Exothermicity of the Ignition Reaction of the Tungsten-Potassium Dichromate System Determined by Quantitative DTA... 

Properties On ignition, reaction between zinc dust and hexachlorethane produces zinc chloride and free carbon, both of which pass off in the smoke. The ammonium perchlorate keeps the reaction going, ammonium chloride readily volatilizes and controls the rate of burning, and calcium carbonate stabilizes the mixture by taking up any hydrochloric acid which may be present. The smoke is harmless. 

Provided that the initial and boundary conditions have been properly selected, Eq. (2.5) describes the effect of an ignition stimulant and of the heat generation from a chemical reaction. The maximum temperature of the inert body (Tcorresponding to the beginning of the autoheating of the system as a result of the ignition reaction, is defined as the ignition temperature ... 

Specifically, a stoichiometric reaction mixture was studied at a pressure of 20 Torr and a residence time of 8 s. Both isothermal and non-isothermal models were considered for a range of temperatures between 500 and 2311 K. The third body M is assumed to be made up from the molecular species H2, O2 and H2O with relative efficiencies of 1 0.4 6, respectively, for all third-body reactions [105]. Although the chemistry is derived from the original Dougherty and Rabitz scheme, the rate data were updated and, where possible, obtained from the CEC evaluation tables [26]. The sources for other reaction rate data are shown in Table 4.3. Oscillating ignition reactions constitute a particularly stringent test of mechanism... 

Inhomogeneities, however caused, can be amplified by pre-ignition reaction. The conditions under which they can give rise to autoignition centres and hot spots have been examined in terms of turbulent structure and simple thermal explosion theory. Bradley [180] assumed the size of an autoignition centre to have the spatial scale of temperature inhomogeneities, distributed about the integral thermal scale of the gas dynamic turbulence. These distributed sizes were compared with computed critical sizes for thermal explosion, for different values of chemical parameters in... 

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