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

Abstract

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.

Investigation of concentration effects on the flame acceleration in vented channels

“…The luminosity of the cellular-like flame wrinkles in the innermost part of the channel increase at the time of arrival of the pressure peaks. The Helmholtz oscillations might be further enhanced by the RayleigheTaylor instability increasing the flame area by producing additional wrinkles when the burnt products pushes towards the denser reactants (Solberg et al, 1981;Cooper et al, 1986;Bauwens et al, 2008Bauwens et al, , 2010. However, due to the high aspect ratio of the rig and the ignition position at the closed end, a significant part of the reactants inside the channel are burnt before the exit of the flame.…”

Effect of hydrogen concentration on vented explosion overpressures from lean hydrogen–air deflagrations

“…In the recent studies [6,7], vented explosions under various experimental conditions were systematically investigated using multiple pressure and flame speed measurements that were synchronized with high-speed videos. From these studies, three main pressure transients were identified, each of which could potentially produce the maximum overall peak overpressure depending on the initial conditions of the experiment.…”

The effect of vent size and congestion in large-scale vented natural gas/air explosions

“…Taylor instabilities are most commonly observed with central ignition and are a contributor to the low frequency oscillatory combustion frequently observed with vented explosions (Bauwens et al, 2010;Bauwens et al, 2009). During the early stage of burnt gas venting, the flame front is accelerated outside of the enclosure creating a 'pear' shaped flame front (in the case of central ignition).…”

“…This increase in venting causes a temporary reduction in the pressure within the enclosure as the rate of venting exceeds the volume expansion due to combustion and the inertia of the outflow 'over-vents' the burnt gases. Secondly, the pressure difference across the vent opening triggers a Helmholtz oscillation, which causes the internal chamber pressure to oscillate about the equilibrium pressure (Bauwens et al, 2010;Bauwens, Chaffee, & Dorofeev, 2009). Thirdly, the onset of burnt gas venting initiates Taylor instabilities, where the less dense burned gas is accelerated into the denser unburned gas/air mixture, increasing the mass combustion rate, and amplifying the Helmholtz oscillation.…”