Deflagrations, Detonations, and the Deflagration-to-Detonation Transition in Methane-Air Mixtures

Explosions in mixtures of natural gas NG and air have been of intense practical concern for coal mines for many years. Potentially explosive mixtures of NG and air can accumulate in the active ventilated areas or in unventilated sealed areas of these mines. If an ignition source, such as a simple spark, ignites the NG-air mixture and creates a flame, the initially slow-moving flame can become turbulent, accelerate rapidly, develop extremely intense pressure waves, and potentially generate enormous stress on coal mine seals. In this work, we attempt to answer the question Given a large enough volume of flammable mixture of NG and air, can a weak spark ignition develop into a detonation Large-scale numerical simulations, in conjunction with experimental work conducted at the National Institute for Occupational Safety and Healths Gas Explosion Test Facility, were performed to address four specific problems flame acceleration and deflagration-to-detonation transition DDT in obstructed channels containing a stoichiometric methane-air mixture, flame acceleration and DDT in fuel-lean and fuel-rich mixtures, effects of spatially varying fuel concentrations on detonations, and stochastic effects on flame acceleration and DDT.