Effect of concentration gradients on the explosion characteristics of methane/air premixed gases

Non-uniform concentration fields increase the risk of combustible gas explosions under practical industrial conditions. To investigate the effects of transverse and vertical concentration gradients on methane explosion characteristics, experiments were conducted near the stoichiometric ratio in a square pipeline, focusing on flame structure, velocity, pressure, and temperature. By adjusting ignition delay time and transverse methane concentration, a non-uniform concentration field was created, and CFD simulations were used to validate the gas distribution. Based on these simulations, the study found that at an ignition delay time of 0, flames propagated forward along the upper wall of the pipeline in an inclined 'tongue' structure. The flame evolved from 'multiple tulip' structures to a forward-moving 'tongue' shape as the ignition delay increased. The internal explosion pressure curve underwent three stages: rapid rise, slow rise, and rapid fall creating a “step” distribution with increased ignition delay. Temperature delays and peak reductions were observed with increased ignition delay and concentration gradients, indicating a decrease in flame propagation speed.