Radiative Ignition

At present there is no small-scale test for predicting whether or how fast a fire will spread on a wall made of flammable or semiflammable (fire-retardant) material. The principal elements of the problem include pyrolysis of solids char-layer buildup buoyant, convective, tmbulent-boundary-layer heat transfer soot formation in the flame radiative emission from the sooty flame and the transient natme of the process (char buildup, fuel burnout, preheating of areas not yet ignited). Efforts are needed to develop computer models for these effects and to develop appropriate small-scale tests. 

Harkelroad, M., Quintiere, J., Walton, W., "Radiative Ignition and Opposed Flow Flame Spread Measurements on Materials", Report No. DOT/FAA-CT-83/28, FAA Technical Center, Atlantic City Airport, N.J., 1983... 

The preceding developments are for an idealized spark ignition system. In actual systems, much of the electrical energy is expended in radiative losses, shock wave formation, and convective and conductive heat losses to the electrodes and flanges. Zeldovich [13] has reported for mixtures that the efficiency... 

Fig. 13.1 Ignition transient process by conductive, convective, and radiative heat.

Fig. 13.3 Radiative ignition criteria of double-base propellants with and without carbon black.

The initial conditions vary with time because the physicochemical process of ignition varies according to the ignition energy supplied to the ignition surface of the energetic material. A typical example of a radiative ignition process is shown below ... 

Fig. 13.3 shows the ignition boundaries of double-base propellants under radiative heating. As the incident radiant flirx intensity. If, increases, the time of radiant heating needed to achieve ignition, X/g, becomes shorter. As the propellant is rendered opaque by the addition of carbon black, X/g becomes shorter at constant If or If becomes smaller at constant X/g. The in-depth absorption is reduced and the majority of the radiative energy is absorbed at the ignition surface of the propellant. 

L. DeLuca et al, Radiative Ignition of Double-Base Propellants. I. Some Formulation Effects , AIAAJoum 14 (7), 940-16 (1976)... 

L. DeLuca et al, Radiative Ignition of Double-Base Propellants I. Some Formulation Effects , AIAAJ 14 (7), 940-6 (1976) CA 85 126780 (1976) [The ign response to arc image radiative heating (5 to lOGcal/sq cm-sec) of several HMX composite propints is shown in Fig 9... 

Figure 2. Maximum allowed impurity concentration for ignition of D-T plasma as a function of plasma temperature assuming radiative losses only. (Reproduced, with permission, from Ref. 22. Copyright 1978, American Nuclear Society.)...

The classical analysis corresponding to the ignition process assumes a linear approximation for the surface re-radiation. The radiative term is then defined as... 

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