On the determination of the laminar burning velocity from closed vessel gas explosions

A methodology to determine the laminar burning velocity from closed vessel gas explosionsis explored. Unlike other methods which have been used to measure burning velocitiesfrom closed vessel explosions, this approach belongs to the categorywhich does not involve visual observation of a rapidly moving flamefront. Only the pressure-time curve is required as experimental input.To verify the methodology, initially quiescentmethane-air mixtures were ignited in a 20-liter explosion sphereand the equivalence ratio was varied from 0.67 to 1.36. The behaviorof the pressure in the vessel was measured as a function of timeand two integral balance models, namely, the thin-flame and the three-zone model,were fitted to determine the laminar burning velocity. Data on the laminar burningvelocity as a function of equivalence ratio, pressure and temperature, measuredby a variety of other methods have been collected from the literature to enablea comparison. Empirical correlations for the effect of pressure andtemperature on the laminar burning velocity have been reviewed and two were selectedto be used in conjunction with the thin-flame model. For the three-zone model, a setof coupled correlations has been derived to describe the effect of pressure and temperatureon the laminar burning velocity and the laminar flame thickness. Ourlaminar burning velocities are seen to fall within the band of data fromthe period 1953-2003. A comparison with recent data from the period 1994-2003shows that our results are 5 to 10% higher than the laminar burning velocitieswhich are currently believed to be the correct ones for methane-air mixtures.Based on this observation it is concluded that the methodology described in thiswork should only be used under circumstances where more accurate methods can not beapplied.