Experimental investigation on downward flame spread over rigid polyurethane and extruded polystyrene foams

An experimental study on combustion performance and flame spread characteristics over liquid diesel and ethanol-diesel blended fuel

: Partial contents: Non-Premixed turbulent combustion; Premixed turbulent combustion; Elementary reactions kinetics; Kinetic mechanisms--models and experiments; Laminar premixed flames; Laminar diffusion flames; Microgravity combustion; Chemical flame inhibition; Fire safety; Spray combustion; Catalytic combustion. p1-16 pages vary. Materials synthesis; Metals combustion; Propellants; NOx formation and control; Soot formation and destruction; Incineration and fuel substitution; Diesel engines; Spark ignition engines; Gas turbines; Active combustion control; High speed combustion; Detonations; Coal and char combustion; Fluidized beds; Porous media, fixed bed combustion, and furnaces,

Twenty-Sixth Symposium (International) on Combustion, Volume 2.

A comparison between the downward flame spread rate for thermally thin samples with one or two inhibited edges is done in multiple situations. The effects of atmospheric composition as well as the width and thickness of a cellulosic-type fuel are tested experimentally. We have found that the normal velocity to the inclined flame front in a side-edge burning is very similar to the downward flame front speed when the sample is inhibited by both edges. Also, the effect of locating a sidewall close to the free edge of the sample is investigated. All these results may be important in order to validate or refute possible models of downward flame spread that take into account side effects.

Experimental Study of the Effects of Side-Edge Burning in the Downward Flame Spread of Thin Solid Fuels

Influence of vertical channel on downward flame spread over extruded polystyrene foam

Experimental study of the channel effect on the flame spread over thin solid fuels

We focus on the front propagation of diffusive flames obtained from the downward burning of inclined thermally thin solid fuels. This process consists of a pyrolysis reaction in the solid-phase and a combustion reaction in the gas phase. The solid-phase model is based on two coupled one-dimensional equations of temperature and solid density. We reduce the system into a single one-dimensional equation from which we obtain an analytical expression for the flame front speed. This expression may be understood as an upper bound of the burning spread rate in inclined samples. The gas-phase model is based on four coupled two-dimensional equations. These are employed to derive a criterion for determining the critical inclination angle beyond which the flame behavior becomes unstable. The comparison with the experiments confirms the validity of our predictions.

Flame front speed and onset of instability in the burning of inclined thin solid fuel samples.

We analyze the flame front speed in the downward combustion of multiple parallel samples of thermally thin fuels at normal gravity and far from extinction conditions. In contrast with the single sample case, where conduction through the gas-phase is the dominant heat transfer mechanism, in the multiple parallel samples case, radiative heat fluxes may become very relevant, which compromises the application of the well-known formula of de Ris for determining the burning rate. Here we study the downward combustion of multiple parallel sheets by (1) obtaining new experimental data at different oxygen atmospheric levels; (2) generalizing a previous comprehensive energy balance model now expected to be valid for a wide range of scenarios; and (3) deriving an analytical approximation for the burning rate that generalizes the classical de Ris formula for those cases where radiative effects cannot be neglected. The comparison with own as well as with external data reveals the strengths and weaknesses of these type...

Energy Balance Models of Downward Combustion of Parallel Thin Solid Fuels and Comparison to Experiments

We derive analytical expressions for the propagation speed of downward combustion fronts of thin solid fuels with a background flow initially at rest. The classical combustion model for thin solid fuels that consists of five coupled reaction-convection-diffusion equations is here reduced into a single equation with the gas temperature as the single variable. For doing so we apply a two-zone combustion model that divides the system into a preheating region and a pyrolyzing region. The speed of the combustion front is obtained after matching the temperature and its derivative at the location that separates both regions. We also derive a simplified version of this analytical expression expected to be valid for a wide range of cases. Flame front velocities predicted by our analytical expressions agree well with experimental data found in the literature for a large variety of cases and substantially improve the results obtained from a previous well-known analytical expression.

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Bruna Comas

Papers

Experimental Study of the Effects of Side-Edge Burning in the Downward Flame Spread of Thin Solid Fuels

Experimental study of the channel effect on the flame spread over thin solid fuels

Flame front speed and onset of instability in the burning of inclined thin solid fuel samples.

Energy Balance Models of Downward Combustion of Parallel Thin Solid Fuels and Comparison to Experiments

Analytical expressions for the flame front speed in the downward combustion of thin solid fuels and comparison to experiments