Detailed numerical calculations based on the solution of the full transport equations have been compared with flamelet calculations in order to analyse the flamelet concept for laminar diffusion flames. The goal of this work is to study the interactive (Lagrangian Flamelet Model and Interactive Steady Flamelet
Model), and non-interactive (Steady Flamelet Model and Enthalpy Defect Flamelet Model) flamelet models considering both differential diffusion and non-differential diffusion situations, and adiabatic and nonadiabatic conditions. Moreover, a new procedure has been employed to obtain enthalpy defects in the flamelet library, the application of which has been found to be encouraging. The effect of using insitu,
local or stoichiometric scalar dissipation rate conditions, and also the effect of using local or stoichiometric conditions to evaluate the flamelet-like time has been analysed. To improve slow species
predictions using the non-interactive models, their transport equations are solved with the reaction terms calculated from the flamelet library, also considering local or stoichiometric conditions in the so-called
Extended Flamelet Models.
The two-equation soot model proposed by Leung et al. [K.M. Leung, R.P. Lindstedt, W.P. Jones, Combust. Flame 87 (1991) 289–305] has been derived in the mixture fraction space. The model has been
implemented using both Interactive and Non-Interactive flamelet strategies. An Extended Enthalpy Defect Flamelet Model (E-EDFM) which uses a flamelet library obtained neglecting the soot formation is proposed
as a Non-Interactive method. The Lagrangian Flamelet Model (LFM) is used to represent the Interactive models. This model uses direct values of soot mass fraction from flamelet calculations. An Extended
version (E-LFM) of this model is also suggested in which soot mass fraction reaction rates are used from flamelet calculations. Results presented in this work show that the E-EDFM predict acceptable results.
However, it overpredicts the soot volume fraction due to the inability of this model to couple the soot and gas-phase mechanisms. It has been demonstrated that the LFM is not able to predict accurately the soot volume fraction. On the other hand, the extended version proposed here has been shown to be very accurate. The different flamelet mathematical formulations have been tested and compared using well verified reference calculations obtained solving the set of the Full Transport Equations (FTE) in the physical space.
The radiation intensity at a given distance depends mainly on the radiative power and the flame’s size and shape.
Considerable literature describing both experimental and theoretical studies of thermal radiation from flames is
available. Even so, predicting the radiant power of large flames is still subject to considerable uncertainty, because
some parameters associated with large turbulent diffusion flames cannot be determined accurately for a given fire.
A series of outdoor large pool-fire experiments were performed using gasoline and diesel fuels lying above a layer
of water. Five concentric circular pools made of reinforced concrete (1.5, 3, 4, 5, and 6 m in diameter) were used.
The experiments were filmed with at least two video cameras registering visible light (VHS) and a thermographic
camera (IR). In this study, thermographic images were used to determine the flames’ distribution of emissive
power, the mean emissive power, and the flame’s irradiance. The contribution of each part of the flame to the total
radiated energy was analyzed. A method is presented combining the IR images and the visible images; it offers
further insight into the relationship between the heat emitted by the luminous part and the obscured, nonluminous,
part of the flame.