Simulation of Flame Propagation

Gamezo, V.N., Ogawa, T. and Oran, E.S., Numerical simulations of flame propagation and DDT in obstructed channels filled with hydrogen-air mixture, Proc. Combust. Inst., 31, 2463,2007. 

Currently, numerical simulations of flame propagation accounting for qualitative mixture compositions and multi-component transports have been widely performed. For example, calculation data of the laminar flame velocity in premixed H2 + air mixtures at atmospheric pressure and room temperature have been published in [27, 38, 54-57]. 

Accidental vapor cloud explosions do not occur under controlled conditions. Various experimental programs have been carried out simulating real accidents. Quantities of fuel were spilled, dispersed by natural mechanisms, and ignited. Full-scale experiments on flame propagation in fuel-air clouds are extremely laborious and expensive, so only a few such experiments have been conducted. 

Over the years, this concept was refined in several ways. A scale dependency was modeled by the introduction of scale-dependent quenching of combustion. The first stage of the process was simulated by quasi-laminar flame propagation. In addition, three-dimensional versions of the code were developed (Hjertager 1985 Bakke 1986 Bakke and Hjertager 1987). Satisfactory agreement with experimental data was obtained. 

To date, many theories and models have been proposed by various researchers, such as Atobiloye and Britter [14], Ashurust [15], Asato et al. [16], and Umemura [17,18]. Numerical simulations have also been conducted by Hasegawa and coworkers [19,20]. Recently, the phenomenon of rapid flame propagation has received keen interest from a practical viewpoint, to realize a new engine operated at increased compression ratios, far from the knock limit [21]. 

Numerical simulation of the flow field during flame propagation in a channel with Dq = 4mm = 0.73). 

Marra, F.S., Analysis of premixed flame propagation in a rotating closed vessel by numerical simulation, Mediterranean Combustion Symposium, Monastir, Tunisia, September 2007. 

Numerical simulation of a spirming detonation in Hj/air mixture in a circular tube at various times. Gray and green space isosurfaces in pressure are the detonation front and the pressure of 6 MPa. White arrow propagating direction of the detonation front, pink arrow rotating direction of the transverse detonation. TD—transverse detonation, and LT—long pressure trail. (Reprinted from Tsuboi, N., Eto, K., and Hayashi, A.K., Combust. Flame, 149,144,2007. With permission.)... 

For the quantification of fire propagation behavior of the FRC materials, 0.10 m wide and 0.61 m long vertical sheets with thickness varying from 3 mm to 5 mm were used. The bottom 0.15 m of the sheet was exposed to 50 kW/m2 of external heat flux in the presence of a 0.01 m long pilot flame to initiate fire propagation. For the simulation of large-scale flame radiation, experiments were performed in k0% oxygen concentration. 

It is interesting to note that stratified combustible gas mixtures can exist in tunnel-like conditions. The condition in a coal mine tunnel is an excellent example. The marsh gas (methane) is lighter than air and accumulates at the ceiling. Thus a stratified air-methane mixture exists. Experiments have shown that under the conditions described the flame propagation rate is very much faster than the stoichiometric laminar flame speed. In laboratory experiments simulating the mine-like conditions the actual rates were found to be affected by the laboratory simulated tunnel length and depth. In effect, the expansion of the reaction products of these type laboratory experiments drives the flame front developed. The overall effect is similar in context to the soap bubble type flame experiments discussed in Section C5c. In the soap bubble flame experiment measurements, the ambient condition is about 300 K and the stoichiometric flame temperature of the flame products for most hydrocarbon fuels... 

Applications. The flame propagation test is used to classify materials into four categories from M.l (nonflammable) to M.4 (highly flammable). In aerospace applications, NASA uses the upward flame propagation test. This test simulates the beginning of a fire with a medium incident heat flux. ... 

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