This study seeks to advance present modelling capabilities in respect of soot and thermal radiation emission from fires. Such developments are crucial to the improved estimate of the hazard potential of accidental fires. Radiation calculation requires the prediction of temperature and the concentrations of all radiatively important species. In hydrocarbon combustion, the key species are carbon dioxide, water vapour, carbon monoxide and particulate soot. In large hydrocarbon fires the latter is usually the dominant radiator. The detailed prediction of the gaseous species in turbulent combustion has previously been shown to be successfully achieved using laminar flamelet modelling in the fast chemistry limit. Soot, however, is governed by relatively slow formation processes which as yet remain poorly understood. The present study proposes a model for soot formation in turbulent non-premixed combustion which aims to address both the slow chemistry and turbulence interaction. In order to circumvent uncertainties in soot formation processes the model relies on empiricism, through the experimental investigation of a sooting laminar diffusion flame. The soot formation model is used to predict soot levels in a jet diffusion flame. Subsequent comparison with experimental data suggests the satisfactory performance of the model, but highlights soot oxidation to be a more significant problem. This stems from uncertainties associated both with instantaneous soot oxidation rate and the highly intermittent nature of this process in turbulent non-premixed flames. The soot formation model is also applied to the prediction of soot levels in a simulated buoyant methane fire, which supplement temperature and gaseous species predictions using a flamelet approach. Detailed predictions of spectrally resolved radiative intensity are then performed and compared with similarly detailed experimental data. The encouraging agreement with experiment allows the assessment of the effect of turbulence-radiation interaction. This is shown to be particularly important in buoyancy-driven fires and is most evident for the luminous radiation. This arises from the soot which is largely confined to narrow sheets that typically lie close to peak temperature zones. A strategy in which more representative soot-temperature correlations may be realised is also described.

A model for the hot slab ignition problem is analyzed to determine critical conditions based on the parameters of the system. Activation energy asymptotics, a singular perturbation approach, is applied to the governing equation resulting in a Volterra integral equation of the second kind whose solution represents the temperature perturbation at the surface of the hot slab. The system is said to be supercritical for given parameter values when the temperature perturbation blows up in small finite time, an indication of ignition, or subcritical when the blow up time is large, indicating that heat loss effects overcome the hot slab ignition mechanisms. Comparison principles for integral equations are used to construct upper and lower solutions of the equation. The exact solution as well as the upper and lower solutions depend on two parameters ε, the Zeldovich number a measure of the heat release and λ, the scaled hot slab size. Upper and lower bounds on the transition region, delineating the super-critical from the sub-critical region, are derived based upon the lower and upper solution behavior. The product integration method is used to compute solutions of the Volterra equation for values of ε and λ in the transition region. The computations indicate that a critical curve, λ(c) lying between the analytic bounds, exists.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.