Full-scale fire modeling combustion

The combustion reaction rate is controlled both by the availability of fuel and oxygen kinetic effects (temperature). In full-scale fire modeling, the resolvable length and time scales are usually much larger than those associated with the scales of the chemical combustion reaction, and it is common to assume that the reactions are infinitely fast. The local reaction rate depends on the rate at which oxygen and fuel are transported toward the surface of stoichiometric mixture fraction, shown in Figure 20.2 as a point where both oxygen and fuel mass fractions go to zero. For almost 20 years, the EBU or eddy dissipation models were the standard models used by the combustion CFD community. With the EBU, in its simplest form, the local rate of fuel consumption is calculated as [3] ... 

The use of laminar flamelet combustion models within FDS have been studied by Yang et al. [42] and Kang and Wen [43], Unfortunately, the performance or advantage over the simple flame-sheet model in large-scale fire simulation was not demonstrated in these studies. In full-scale calculations, the mixture fraction and temperature fields close to the flame sheet have overshoots, caused by the second-order transport scheme. It is still unclear how the laminar flamelet models that require both second and first moments of the local mixture fraction field could work in this situation. 

Fires are, in general, very complex in nature. The complexify arises because of interaction of phenomenon of turbulence, combustion, radiation, etc., which control fire and smoke development with each other and with the surroundings. Reduced-scale experiments although provide useful information, yet they alone are not sufficient to reproduce full-scale features whereas the full scale experiments are costly and expensive. In marine industry, full scale experiments are ruled out due to high initial investment and resource scarcity. Therefore, solution to this lies on mathematical modeling, although, the results should be validated with reduced or full scale experiments wherever possible to find a practical solution. 

There are three kinds of models of fires, (1) based on computational fluid dynamics (CFD) of the combustion process of fire, (2) phenomenological models and (3) empirical or semi-empirical models based on full scale tests. 

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