Minimum ignition energy , flame

Turbulent Diffusion FDmes. Laminar diffusion flames become turbulent with increasing Reynolds number (1,2). Some of the parameters that are affected by turbulence include flame speed, minimum ignition energy, flame stabilization, and rates of pollutant formation. Changes in flame stmcture are beHeved to be controlled entirely by fluid mechanics and physical transport processes (1,2,9). 

Minimum Ignition Energy (MIE) Initiation of flame propagation in a combustible mixture requires an ignition source of adequate energy and duration to overcome heat losses to the cooler surrounding material. Dust and vapor... 

The answer is "NO." In the combustible mixture, an electric spark produces a flame kernel. Initially, its shape is elliptical (like an American football), and then becomes a torus (like an American doughnut). Afterwards, it changes into almost spherical shape, and propagates spherically in the unbumed mixture. This process is formed by the existence of spark electrodes, which is necessary for spark discharge. Spark electrodes lead not only to heat loss from the flame kernel but also a change in the kernel shape. Both affect the minimum ignition energy. 

Eckhoff, R. K., Toward a minimum ignition energy for dust clouds, Comb, and Flame, 24 53-64(1975)... 

Hydrogen is produced or used in gas or liquid form in a number of processes. Hydrogen is a colorless, odorless gas that is easily ignited over a wide flammable range. Hydrogen burns very rapidly and cleanly in air with a nearly invisible clear blue flame. It has flammable limits of 4-74% in air and minimum ignition energy of 0.02 mj, compared to 0.25 mj for typical hydrocarbons. 

Quantitative development of the above model of the ignition process is overwhelmingly complicated. Lewis Von Elbe therefore chose to attempt correlation of experimental minimum ignition energies with some energy functions computed from minimal flame parameters... 

Ballal, D.R., and Lefebvre, A.H., The influence of spark discharge characteristics on minimum ignition energy in flowing gases, Combustion and Flame, 24, 99-108, 1975. 

Ko, Y., Anderson, R. W. and Arpaci, V. S. Spark ignition of propane-air mixtures near the minimum ignition energy, Part I An experimental study, Combustion and Flame 83,1991, 75-87... 

FIGURE 1.21 Minimum ignition energy vs. oxidizer composition for an atmospheric pressure, stoichiometric CH4 flame. (Adapted from Lewis, B. and von Elbe, G., Combustion, Flames and Explosions of Gases, 3rd ed., Academic Press, New York, 1987.)... 

A proven ignition energy source should be used. The igniters should be proven for both quality (i.e., that an ignition flame exists) and quantity (i.e., that a minimum ignition energy is available for the main burner). 

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