Pre-ignition reaction

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... 

The rocket fuel blend of cardanol (20 parts), norbornadiene (40 parts) and carene (40 parts) exhibit synergistic spontaneous ignition with an oxidiser such as red fuming nitric acid (ref. 275) and copolymerisation has been found to be one of the pre-ignition reactions (ref. 276). 

For this reason, in order to enkindle the fuel mixture, it is not necessary to heat it up to the temperature of self-ignition ti. It suffices to raise the tempa-ature of the surrounding medium to tb and then wait for a determined time period required for the spontaneous pre-ignition reactions to take place. 

S. Patai and E. Hoffmann, Pre-ignition Reactions of Some Combustible Solids with Solid Oxidants, J, Appl. Chem. (London), 2, 8 (1952). 

DSC analysis of Zinc/PTFE mixtures reveals a pre-ignition reaction commencing at 270°C that is followed by both fusion endotherm signal of PTFE and Zinc (Figure 5.21). At the fusion point of Zinc the actual combustion reaction starts vigorously. In nitrogen atmosphere the combustion reaction is delayed and does not start at the fusion of Zn [24]. 

Koch, E.-C. (2004) Pre-ignition reactions in metal/organohalogen pyrolants. 35th International Annual Conference of ICT, Karlsruhe, June 29-2 July, p. 126. 

The onset temperature of the pre-ignition reaction, TpiR, is usually independent of the melting or decomposition temperature of the oxidizer but related to the thermodynamic melting temperature, Tmeit of the metal ... 

Explosive materials are ignited by the action of an external stimulus which effectively inputs energy into the explosive and raises its temperature. The external stimulus can be friction, percussion, electrical impulse, heat, etc. Once stimulated the rise in temperature of the explosive causes a sequence of pre-ignition reactions to commence. These involve transitions in the crystalline structure. 

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

The important point to note here is that nearly all of the pre-ignition steps, including two endothermic reactions, take place in the vapour phase. Thus, if ignition is to occur at low pressures, sufficient heat energy must be available for a sufficient time period ... 

In this scheme, Reaction 1 represents a direct (pre-ignition) combustion reaction which may or may not be accompanied by formation of carbon monoxide Reaction 2 describes the oxidation reaction (and its sequences) examined in the present study. B and C in Reaction 2 denote degradation products of humic acids (e.g. hymatomelanic, fulvic, and/or so-called water soluble coal acids), and ki,, etc. represent the corresponding rate constants. 

The test equipment shown in a schematic drawing in the method consists of a test flask, a furnace, a temperatiue controller, a syringe, a thermocouple and other auxiliary parts. The measurement is performed in a dark room for optimum visual detection of cool flames. The results are reported as ignition temperature, time lags (delay between sample insertion and material ignition), and reaction threshold temperature (the lowest flask temperature at which nonluminous pre-flame reactions (e.g., temperature rise) occur). 

Biological catalysts are known as enzymes (Chapter 23 on the accompanying website) and consist of proteins, often associated with metal ions. A substance that decreases the rate of a reaction is called an inhibitor. An example of an inhibitor is the anti-knock compound, tetraethyl lead(iv), which was used to prevent pre-ignition in leaded petrol vapour but has now been banned in practically all countries (Chapter 10). There are many specific and general inhibitors known for enzymes many nerve gases and poisons, for example cyanides, operate as enzyme inhibitors, often by interacting with the active site of the enzyme (Figure 6.13). 

Hogan, V.D. and Gordon, S. (1959) Pre-ignition and ignition reactions of the propagatively reacting system magnesium-sodium nitrate-laminae. Combust. Flame, 3, 3. 

Pre-ignition and ignition reactions of the system barium peroxide-magnesium[Pg.77]

Hicks showed that the time required to achieve ignition depends on the manner in which the external heat flux is applied. If the propellant surface is heated continuously, the surface temperature will continue to rise until runaway reaction conditions are reached [curve (a) of Fig. 3]. If the heat flux is terminated just before runaway reaction conditions pre achieved, then a sudden drop in surface temperature can occur, followed by a long time-delay before the surface temperature again begins to mse [as shown in curve (b)]. If the flux is removed too soon, the temperature will drop continuously and ignition will not be achieved [as shown in curve (c)]. 

Bench-scale reaction-to-fire tests are used to characterize the behavior of materials under more severe thermal exposure conditions that are representative of the growing pre-flashover stage of a compartment fire. These tests essentially determine how a material responds to the temperatures and heat fluxes in a growing fire. In these tests, the fire conditions are simulated with a radiant panel or by inserting the specimen into a small furnace. A pilot may be used to ignite the flammable gases and vapors that are generated as a result of thermal decomposition of the... 

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