End-wall ignition of methane-air mixtures under the effects of CO₂/Ar/N₂ fluidic jets

Methane is a fuel with wide applications in daily life and industrial production, mainly due to its suitable performance in producing more heat per mass and less carbon dioxide per unit of heat released. Methane is flammable, and therefore, its safety issues in the process of storage and transportation due to its potential explosion risk must be prioritized first and foremost. Due to wind or obstacles in the explosion process, most explosions take place in a turbulent environment; hence, investigations related to the effect of turbulence on the explosion process require in-depth examination. In this study, a methane-air mixture under standard conditions (T₀ = 298 K, p₀ = 100 kPa) is selected as the test mixture, and the effect on explosion parameters, i.e., p_max, τ_e and (dp/dt)_max, is investigated by the turbulence produced by three different inert additives (CO₂, Ar, and N₂). Explosion tests are first performed under quiescent conditions and then compared with cases under turbulent conditions. Under quiescent conditions, the explosion overpressure in the end-wall ignition case is approximately 40% lower than that in the central ignition case. In end-wall ignition, the incident precursor shock is weaker and the heat loss is higher than those in central ignition. By introducing turbulence, the value of p_max is greatly enhanced and τ_e is reduced, indicating that turbulence greatly improves the explosion hazard. By adjusting the pressure difference in the fluidic jet and spherical chamber, i.e., p_J0/p₀, the turbulence intensity is accordingly changed. Under the condition of a higher p_J0/p₀, the higher turbulence intensity better promotes the chemical reaction and explosion process, and the values of explosion parameters increase linearly with the turbulence intensity. The turbulence-enhancing effect on explosion is more prominent near the flammability limit than under stoichiometric conditions. Compared with that under fuel-rich condition, explosion depends less on the turbulence properties at the fuel-lean side. Turbulence generated by CO₂ has the best effect on enhancing explosion when approaching the fuel-rich limit.