A fire whirl may occur when a pool fire interacts with a swirling flow. This paper discusses the mechanism of flame-height increase of laboratory-scale axisymmetric fire whirls. The classical Burke-Schumann theory is first extended to include swirling flows. By applying a coordinate transformation, it is shown that the dimensionless flame height (flame height divided by pool diameter) is proportional to the Reynolds number (based on the fuel evaporation rate) regardless of the presence of swirling flow. Thus, swirling flows have no direct impact on the flame height of a pool fire. Instead, the presence of a swirling flow changes the shape of flame base, increasing the heat flux to the liquid surface and hence the fuel evaporation rate; the flame height is then increased because it is proportional to the fuel evaporation rate. These theoretical findings are validated by a series of numerical simulations conducted in this study as well as previous studies by other researchers.

This paper proposes a unified model that can be applied to the premixed and diffusion flames based on the author's premixed combustion model [1-8]. The proposed model has the following features. 1) It includes the laminar flame speed and the gradient of the mixture fraction as parameters. When the gradient of the mixture fraction is close to zero, the model is also close to the previous premixed combustion model as an asymptotic form. 2) It considers the effects of pressure in the combustor, unburned gas temperature, and flame stretch on combustion based on the laminar flame speed. 3) The effect of turbulence is considered through the turbulent eddy viscosity of all turbulence models. To verify the accuracy of the model, the turbulent opposed diffusion flame presented by Mastorakos [9] was numerically simulated, as an example of a turbulent diffusion flame. The overall thickness of temperature and mass fraction profiles were in good agreement with experimental data. These comparisons with the experimental data and this agreement confirmed the proposed unified model was able to accurately simulate diffusion flame under the certain flame stretch.

In the present study, propagation of detonation in a supersonic combustible flow was experimentally studied as a first step to realize the behavior of standing detonation for hypersonic propulsion. Experiments were performed in the detonation tube combined with a shock tube providing the supersonic flow of a stoichiometric oxyhydrogen. The flow Mach number behind the incident shock wave was estimated to be 1.2. The experimental results show that depending on the flow velocity, the apparent propagation velocity of detonation in the supersonic flow is higher in the upstream and lower in the downstream direction than the Chapman-Jouguet (CJ) velocity. The smoked plate records demonstrate cellular patterns deformed in the flow direction, which is due to velocity change of the leading shock front constructing the cellular structure. The calculated aspect ratios of the cell agree well with the experimental ones under the assumption that the velocity of the transverse wave is not affected by the flowing mixture.