Sergey B. Dorofeev

Effect of Ignition Location, Vent Size, and Obstacles on Vented Explosion Overpressures in Propane-Air Mixtures

The authors present results of vented explosion tests using stoichiometric propane-air mixtures in a room-size enclosure 63.7 m3 in volume. The tests were focused on the effect of ignition location, vent size, and obstacles on explosion development and pressure buildup. The dependence of the maximum pressure generated on the experimental parameters was analyzed. It was found that the pressure maxima may be caused by pressure transients defined by the interplay of several factors, such as the maximum flame area and burning velocity in the chamber, and the overpressure generated by the external explosion. A simple model was proposed that allowed for the estimation of the maximum pressure for each of the main pressure transients. The model was found to agree with the experimental data within the experimental uncertainty.

Experimental and Numerical Study of Methane-air Deflagrations in a Vented Enclosure

Results of a series of tests on the deflagration of methane-air mixtures in a large vented enclosure are presented. Experiments were made in FM Global’s 63.7 m 3 chamber. The chamber was 4.6 x 4.6 x 3.0 m with a vent opening on one side. Vent areas of either 2.7 or 5.4 m 2 were used. Tests were performed with ignition either at the center of the chamber or at the center of the wall opposite the vent. Methane-air mixtures with methane concentrations close to 9.5% vol. were used in the tests. Pressure data, as function of time, and flame time-of-arrival data were obtained both inside and outside the chamber near the vent. Detailed experimental data is used in the paper to test a three-dimensional gasdynamic model for the simulation of gaseous combustion in vented enclosures. The model is based on a Large Eddy Simulation (LES) solver created using the OpenFOAM CFD toolbox using sub-grid turbulence and flame wrinkling models. Results from the calculations are compared with the experimental data. The capabilities and deficiencies of the model are discussed.

A flame speed correlationfor unconfined gaseous explosions

An approximate method for description of flame acceleration in congested areas filled with combustible gases is presented. The method takes into account both the flame folding arising from interactions with obstacles of the flow produced by the flame and the increase of the burning rate resulting from turbulence generated in the flow ahead of the flame. A simple analytical expression for the flame speed is suggested. Coefficients in this correlation are determined by fitting the model predictions with a set of experimental data. This correlation is then used to evaluate the maximum flame speed that may be developed in vapor cloud explosions as a function of scale and obstacle density. As an example of applications, the flame speeds are evaluated for four typical fuels: methane, propane, ethylene, and hydrogen, and for three different levels of congestion. Both ideal stoichiometric mixtures of the four fuels with air and clouds with nonuniform concentration distributions are considered. The method is shown to take appropriate account of mixture properties. In particular, the well‐known difference in combustion behavior of methane, propane, ethylene, and hydrogen was well captured by the method. On the basis of the maximum flame speeds, the severity of the blast effect from unconfined gaseous explosions is evaluated. The results are compared with other methods for evaluation of the blast effect from unconfined vapor cloud explosions.

Effects of the primary explosion site and bulk cloud in VCE prediction: A comparison with historical accidents

A model for predicting vapor cloud explosion blast loads is described extending a previously developed model. The model considers the contribution of a Primary Explosion Site (PES) as well as the bulk effect of the total flammable cloud. The model results are then compared with historical accidents and other commonly used models considering a single PES. Four historical events are examined: the Flixborough accident of 1974, the Texas City accident of 2005, the Phillips 66 accident of 1989, and the Buncefield incident of 2005. It is found that the combined model produced pressure and impulse values consistent with the damage observed. If the contribution of the total cloud is not considered, the far field pressure, which included overpressures up to 0.35 bar, was underpredicted and impulse was significantly underpredicted. The other methods, produced, in general, significantly lower overpressures and impulses when compared with the damage indicators seen in the explosion accidents.

A new methodology to evaluate system‐level performance of explosion suppression systems

A parametric experimental study was performed to understand the effect of various factors on the explosion suppression phenomenon. Full‐scale suppression experiments were conducted in FM Globals 2.5 and 25 m3 vessels. Either quiescent propane‐air or cornstarch‐air explosions were suppressed using a 2.5, 5, 10, or 50 L suppressant bottle, filled with sodium bicarbonate and pressurized with nitrogen to approximately 62 bar. The growth of the suppressant cloud in the open atmosphere was also measured in conjunction with the pressure drop in each size of suppressant bottle. From these results, it was found that an expanding flame must be entirely enveloped by suppressant for successful suppression of the flame to occur. Based on this concept, a simple physics‐based model was developed to determine the maximum protected throw distance, surface area, and volume of a single suppressant bottle (as part of a suppression system). This can be easily scaled to larger volumes than what was used in the experiments.

An Experimental Study of Complex Fuel Burning Behavior Using Characteristic Fuel Unit Approach

This experimental work studies the burning behavior of a representative complex fuel used for industrial fire testing. The selected fuel is the cartoned unexpended plastic (CUP) commodity, which is complex due to multiple combustible materials and intricate geometry that are beyond detailed treatment by current numerical modeling capabilities. The objectives of this work are to design an experimental method for characterizing the burning behavior of a complex fuel at scales represented by a characteristic fuel unit and to explore this behavior for the CUP commodity. A series of freeburn experiments were conducted to measure global quantities such as heat release rate and local thermal impact variables such as surface heat flux and gas temperature. A long-wave infrared camera was also used to reveal burning phenomena of the complex fuel, including corrugated cardboard delamination and plastic melting. The measurements are currently being used to develop a simple model describing the thermal degradation of the complex fuel with satisfactory results. The present work helps understand the unique burning behavior of complex fuels and provides data for numerical model development and validation.

Laminar Smoke Point Based Subgrid Soot Radiation Modeling Applied to LES of Buoyant Turbulent Diffusion Flames

Large eddy simulations (LES) of gaseous buoyant turbulent flames have been conducted with the application of a flamelet based soot-radiation model. The subgrid model applies a turbulent eddy description of soot formation, oxidation and radiation and is based on the laminar smoke point concept. Two parameters, a local turbulent strain rate and prior enthalpy loss/gain fraction influence the soot formation and radiation. Radiation heat transfer is simulated by solving the finite volume discretized form of the radiative transfer equation (RTE) with the subgrid soot-radiation model implemented. The radiant heating of surfaces in close proximity of the flames is computed and predicted heat fluxes and surface temperatures are compared against experimental data. Fire growth in a rack storage arrangement is simulated with the application of a pyrolysis model. Computed heat release rate (HRR) is compared against experimental data.