Large-Scale Experiments and Absolute Detonability of Methane/Air Mixtures

Abstract

The Gas Explosions Research Facility at Lake Lynn Experimental Mines was used to determine the detonability limit of methane for a 1-meter diameter tube as a function of the percent of methane in air. The measurements showed detonation limits of 5.3% (lean) and 15.6% (rich). A method for extrapolating these limits to larger systems, more relevant to coal mine tunnels, was proposed based on a simple scaling law and some empirical information on the number of cells required for a detonation to propagate in closed, open, and partially open geometries. The scaling law reproduces the measured detonation-cell sizes measured in the 1-m tube. Applying this to a tunnel the size of a coal mine produces a detonability limit less than the currently measured flammability limit for methane/air at atmospheric conditions, which raises interesting questions for detonation and combustion theory and suggests measurements in larger tubes.

Mechanisms and Occurrence of Detonations in Vapor Cloud Explosions

“…In most cases, detonation cell patterns are highly irregular, but characteristic structures can be identified. At the rich and lean detonability limits, these structures can be extremely large, as shown in [21]. When the numerical simulation shown in Figure 2.2 finally produced a detonation, there were horizontal lines across the front of the propagating shock front.…”

“…Then, depending on the mixture and system geometry, the turbulent flame system may transition to one in which there is a detonation wave. This configuration has been studied extensively experimentally (see, e.g., [17,18,19,20,21]) and by large-scale numerical simulations (see, e.g., [22,23,24,11,12]) in many laboratories and for many types of flammable gas, system sizes, and channels with and without obstacles.…”

“…This experimental becomes more difficult at the detonation limits where very large amounts of energy are required. Reference [21] discuss possible ways to extrapolating the minimum energy required for direct initiation based on known or more easily measured detonation parameters. From these experiments, however, we at least know whether a mixture is detonable.…”

“…Another possible way to assess detonability was suggested in [21]. They combined the data obtained in the Lake Lynn experiments, described above for direct ignition of methane in air, with a scaling law based on properties of detonation cells in measurable regimes.…”

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“…Применительно к угольным шахтам современные подходы к моделированию ускорения пламени и перехода горения в детонацию в газовоздушных смесях приведены в работах [26][27][28][29]. Экспериментальные данные о характере перехода горения в детонацию метано-воздушных смесей представлены в работах [30][31][32][33][34].…”