Dynamics of fuel-lean and stoichiometric methane-air explosion venting: Experiments and simulations

The computational explosion venting analyzer (EVA), a zero-dimensional (0D) model based on the conservation of mass and energy, is being developed to model centrally- and rear-ignited explosions. For this purpose, a series of explosion venting experiments in a cylinder with vent areas of 132.7, 86.6, 67.9 cm2 (corresponding to the vent area ratios of K = 0.47, 0.31, 0.24, respectively) is performed. Two equivalence ratios of phi= 0.8 and 1 are considered to represent the fuel-lean and stoichiometric methane-air mixtures, respectively. The dynamics of explosions is studied through the observation of flame propagation and pressure measurements. In rear ignition experiments, laminar, so-called "finger flame" propagation is observed, while in the case of center ignition, a flame initially expands spherically and then is pulled by the vent, acquiring a half-elliptical and half-spherical shape. The peak pressures obtained from rear ignition exceed their counterparts in the center ignition experiments. The EVA is compared with the experimental matrix. No turbulence is implemented in stoichiometric simulations, and slight turbulence has been accounted for in the lean mixture simulations. It is found that the large vent, generally, imposes more disturbances on the flame shape and the fuel-lean mixtures are more prone to the diffusional-thermal instabilities. It is shown that such a simple numerical tool, as the EVA is, can estimate a complicated problem such as pressure evolution resulted from a vented gas explosion.